diff --git a/.github/ISSUE_TEMPLATE/bug.md b/.github/ISSUE_TEMPLATE/bug.md
new file mode 100644
index 00000000..2cfa7778
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/bug.md
@@ -0,0 +1,25 @@
+---
+name: Bug report
+about: Report a problem and provide necessary context
+title: 'Fix ...'
+labels: 'bug'
+
+---
+
+
+## What's wrong
+
+
+
+## How it should work?
+
+
+
+## Checklist before calling for maintainers
+
+* [ ] Have you checked to ensure there aren't other open [Issues](../issues) for the same problem?
+
diff --git a/.github/ISSUE_TEMPLATE/new_snippet.md b/.github/ISSUE_TEMPLATE/new_snippet.md
new file mode 100644
index 00000000..6bb19dc9
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/new_snippet.md
@@ -0,0 +1,23 @@
+---
+name: New snippet
+about: Suggest new gotcha and try to explain it
+title: 'New snippet: ...'
+labels: 'new snippets'
+---
+
+
+## Description
+
+## Snippet preview
+
+## Checklist before calling for maintainers
+
+* [ ] Have you checked to ensure there aren't other open [Issues](../issues) for the same update/change?
+* [ ] Have you checked that this snippet is not similar to any of the existing snippets?
+
+* [ ] Have you added an `Explanation` section? It shall include the reasons for changes and why you'd like us to include them
+
diff --git a/.github/ISSUE_TEMPLATE/translation.md b/.github/ISSUE_TEMPLATE/translation.md
new file mode 100644
index 00000000..37ea4c3a
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/translation.md
@@ -0,0 +1,13 @@
+---
+name: Translation
+about: Request a new traslation and start working on it (if possible)
+title: 'Translate to ...'
+labels: 'translations'
+
+---
+
+
+## Checklist before calling for maintainers
+
+* [ ] Have you checked to ensure there aren't other open [Issues](../issues) for the same translation?
+* [ ] Do you wish to make a translation by yourself?
diff --git a/.github/PULL_REQUEST_TEMPLATE/common.md b/.github/PULL_REQUEST_TEMPLATE/common.md
new file mode 100644
index 00000000..ab9f34ad
--- /dev/null
+++ b/.github/PULL_REQUEST_TEMPLATE/common.md
@@ -0,0 +1,13 @@
+## #(issue number): Summarize your changes
+
+
+
+Closes # (issue number)
+
+## Checklist before requesting a review
+
+- [ ] Have you followed the guidelines in [CONTRIBUTING.md](../CONTRIBUTING.md)?
+- [ ] Have you performed a self-review?
+- [ ] Have you added yourself into [CONTRIBUTORS.md](../CONTRIBUTORS.md)?
+
diff --git a/.github/PULL_REQUEST_TEMPLATE/new_snippet.md b/.github/PULL_REQUEST_TEMPLATE/new_snippet.md
new file mode 100644
index 00000000..dab5816f
--- /dev/null
+++ b/.github/PULL_REQUEST_TEMPLATE/new_snippet.md
@@ -0,0 +1,15 @@
+## #(issue number): Summarize your changes
+
+
+
+Closes # (issue number)
+
+## Checklist before requesting a review
+
+- [ ] Have you written simple and understandable explanation?
+- [ ] Have you added new snippet into `snippets/` with suitable name and number?
+- [ ] Have you updated Table of content? (later will be done by pre-commit)
+- [ ] Have you followed the guidelines in [CONTRIBUTING.md](../CONTRIBUTING.md)?
+- [ ] Have you performed a self-review?
+- [ ] Have you added yourself into [CONTRIBUTORS.md](../CONTRIBUTORS.md)?
diff --git a/.github/PULL_REQUEST_TEMPLATE/translation.md b/.github/PULL_REQUEST_TEMPLATE/translation.md
new file mode 100644
index 00000000..74f88005
--- /dev/null
+++ b/.github/PULL_REQUEST_TEMPLATE/translation.md
@@ -0,0 +1,13 @@
+## #(issue number): Translate to ...
+
+
+
+Closes # (issue number)
+
+## Checklist before requesting a review
+
+- [ ] Have you fetched the latest `master` branch?
+- [ ] Have you translated all snippets?
+- [ ] Have you followed the guidelines in [CONTRIBUTING.md](../CONTRIBUTING.md)?
+- [ ] Have you performed a self-review?
+- [ ] Have you added yourself into [CONTRIBUTORS.md](../CONTRIBUTORS.md)?
diff --git a/.github/workflows/pr.yml b/.github/workflows/pr.yml
new file mode 100644
index 00000000..8356b6f8
--- /dev/null
+++ b/.github/workflows/pr.yml
@@ -0,0 +1,28 @@
+on: [pull_request]
+
+permissions:
+ contents: read
+ pull-requests: read
+ checks: write
+
+concurrency:
+ group: ${{ github.workflow }}-${{ github.ref }}
+ cancel-in-progress: true
+
+jobs:
+ lint:
+ runs-on: ubuntu-latest
+ steps:
+ - uses: actions/checkout@v4
+ - name: Write git diff to temp file
+ run: |
+ git fetch origin
+ git diff origin/${{ github.base_ref }} *.md translations/*/*.md \
+ | sed -n '/^+/p' | sed '/^+++/d' | sed 's/^+//' \
+ > ${{ runner.temp }}/diff.md
+ - name: Output diff
+ run: cat ${{ runner.temp }}/diff.md
+ - name: Check diff with markdownlint
+ uses: DavidAnson/markdownlint-cli2-action@v17
+ with:
+ globs: "${{ runner.temp }}/diff.md"
diff --git a/.gitignore b/.gitignore
index 057dcb0c..7a88626b 100644
--- a/.gitignore
+++ b/.gitignore
@@ -2,9 +2,6 @@
node_modules
npm-debug.log
-wtfpython-pypi/build/
-wtfpython-pypi/dist/
-wtfpython-pypi/wtfpython.egg-info
# Python-specific byte-compiled files should be ignored
__pycache__/
@@ -16,3 +13,8 @@ irrelevant/.ipynb_checkpoints/
irrelevant/.python-version
.idea/
+.vscode/
+
+# Virtual envitonments
+venv/
+.venv/
diff --git a/.markdownlint.yaml b/.markdownlint.yaml
new file mode 100644
index 00000000..09e4e924
--- /dev/null
+++ b/.markdownlint.yaml
@@ -0,0 +1,17 @@
+MD013:
+ line_length: 120
+
+# no-duplicate-heading - Multiple headings with the same content (Ignore multiple `Explanation` headings)
+MD024: false
+
+# no-trailing-punctuation - Trailing punctuation in heading (Ignore exclamation marks in headings)
+MD026: false
+
+# no-inline-html : Inline HTML (HTML is used for centered and theme specific images)
+MD033: false
+
+# no-inline-html : Bare URL used (site should be attributed transparently, because otherwise we have to un-necesarily explain where the link directs)
+MD034: false
+
+# first-line-h1 : First line in a file should be a top-level heading (Ignore because diff file will never have valid heading)
+MD041: false
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 00000000..8c241c39
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,7 @@
+default_language_version:
+ python: python3.12
+repos:
+- repo: https://github.com/DavidAnson/markdownlint-cli2
+ rev: v0.17.0
+ hooks:
+ - id: markdownlint-cli2
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index dd9049d4..771ece8a 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -1,8 +1,19 @@
+# Contributing
+
+## Getting Started
+
+Contributions are made to this repo via Issues and Pull Requests (PRs). A few general guidelines that cover both:
+
+- Search for existing Issues and PRs before creating your own.
+- We work hard to makes sure issues are handled in a timely manner but, depending on the impact, it could take a while to investigate the root cause. A friendly ping in the comment thread to the submitter or a contributor can help draw attention if your issue is blocking.
+
+## Issues
+
All kinds of patches are welcome. Feel free to even suggest some catchy and funny titles for the existing Examples. The goal is to make this collection as interesting to read as possible. Here are a few ways through which you can contribute,
-- If you are interested in translating the project to another language (some people have done that in the past), please feel free to open up an issue, and let me know if you need any kind of help.
+- If you are interested in translating the project to another language, please feel free to open up an issue using `translation` template, and let me know if you need any kind of help.
- If the changes you suggest are significant, filing an issue before submitting the actual patch will be appreciated. If you'd like to work on the issue (highly encouraged), you can mention that you're interested in working on it while creating the issue and get assigned to it.
-- If you're adding a new example, it is highly recommended to create an issue to discuss it before submitting a patch. You can use the following template for adding a new example:
+- If you're adding a new example, it is highly recommended to create an issue using `new_snippet` template to discuss it before submitting a patch. You can use the following template for adding a new example:
### ▶ Some fancy Title *
@@ -33,31 +44,22 @@ Probably unexpected output
```
+## Pull requests
-Few things that you can consider while writing an example,
-
-- If you are choosing to submit a new example without creating an issue and discussing, please check the project to make sure there aren't similar examples already.
- Try to be consistent with the namings and the values you use with the variables. For instance, most variable names in the project are along the lines of `some_string`, `some_list`, `some_dict`, etc. You'd see a lot of `x`s for single letter variable names, and `"wtf"` as values for strings. There's no strictly enforced scheme in the project as such, but you can take a glance at other examples to get a gist.
- Try to be as creative as possible to add that element of "surprise" in the setting up part of an example. Sometimes this may mean writing a snippet a sane programmer would never write.
- Also, feel free to add your name to the [contributors list](/CONTRIBUTORS.md).
-**Some FAQs**
-
- What is is this after every snippet title (###) in the README: ? Should it be added manually or can it be ignored when creating new snippets?
-
-That's a random UUID, it is used to keep identify the examples across multiple translations of the project. As a contributor, you don't have to worry about behind the scenes of how it is used, you just have to add a new random UUID to new examples in that format.
-
- Where should new snippets be added? Top/bottom of the section, doesn't ?
-
-There are multiple things that are considered to decide the order (the dependency on the other examples, difficulty level, category, etc). I'd suggest simply adding the new example at the bottom of a section you find more fitting (or just add it to the Miscellaneous section). Its order will be taken care of in future revisions.
-
- What's the difference between the sections (the first two feel very similar)?
-
-The section "Strain your brain" contains more contrived examples that you may not really encounter in real life, whereas the section "Slippery Slopes" contains examples that have the potential to be encountered more frequently while programming.
-
- Before the table of contents it says that markdown-toc -i README.md --maxdepth 3 was used to create it. The pip package markdown-toc does not contain either -i or --maxdepth flags. Which package is meant, or what version of that package?
- Should the new table of contents entry for the snippet be created with the above command or created manually (in case the above command does more than only add the entry)?
-
-We use the [markdown-toc](https://www.npmjs.com/package/markdown-toc) npm package to generate ToC. It has some issues with special characters though (I'm not sure if it's fixed yet). More often than not, I just end up inserting the toc link manually at the right place. The tool is handy when I have to big reordering, otherwise just updating toc manually is more convenient imo.
+## Common questions
+
+- What is is this after every snippet title (###) in the README: ? Should it be added manually or can it be ignored when creating new snippets?
+ - That's a random UUID, it is used to keep identify the examples across multiple translations of the project. As a contributor, you don't have to worry about behind the scenes of how it is used, you just have to add a new random UUID to new examples in that format.
+- Where should new snippets be added? Top/bottom of the section, doesn't ?
+- There are multiple things that are considered to decide the order (the dependency on the other examples, difficulty level, category, etc). I'd suggest simply adding the new example at the bottom of a section you find more fitting (or just add it to the Miscellaneous section). Its order will be taken care of in future revisions.
+- What's the difference between the sections (the first two feel very similar)?
+ - The section "Strain your brain" contains more contrived examples that you may not really encounter in real life, whereas the section "Slippery Slopes" contains examples that have the potential to be encountered more frequently while programming.
+- Before the table of contents it says that `markdown-toc -i README.md --maxdepth 3` was used to create it. The pip package `markdown-toc` does not contain neither `-i` nor `--maxdepth` flags. Which package is meant, or what version of that package? Should the new table of contents entry for the snippet be created with the above command or created manually (in case the above command does more than only add the entry)?
+ - `markdown-toc` will be replaced in the near future, follow the [issue](https://github.com/satwikkansal/wtfpython/issues/351) to check the progress.
+ - We use the [markdown-toc](https://www.npmjs.com/package/markdown-toc) npm package to generate ToC. It has some issues with special characters though (I'm not sure if it's fixed yet). More often than not, I just end up inserting the toc link manually at the right place. The tool is handy when I have to big reordering, otherwise just updating toc manually is more convenient imo.
If you have any questions feel free to ask on [this issue](https://github.com/satwikkansal/wtfpython/issues/269) (thanks to [@LiquidFun](https://github.com/LiquidFun) for starting it).
diff --git a/README.md b/README.md
index e7491373..e4afe016 100644
--- a/README.md
+++ b/README.md
@@ -1,21 +1,41 @@
-
+
+
+
+
+
+
+
+
What the f*ck Python! 😱
Exploring and understanding Python through surprising snippets.
+Translations: [Chinese 中文](https://github.com/leisurelicht/wtfpython-cn) |
+[Vietnamese Tiếng Việt](https://github.com/vuduclyunitn/wtfptyhon-vi) |
+[Spanish Español](https://web.archive.org/web/20220511161045/https://github.com/JoseDeFreitas/wtfpython-es) |
+[Korean 한국어](https://github.com/buttercrab/wtfpython-ko) |
+[Russian Русский](https://github.com/satwikkansal/wtfpython/tree/master/translations/ru-russian) |
+[German Deutsch](https://github.com/BenSt099/wtfpython) |
+[Persian فارسی](https://github.com/satwikkansal/wtfpython/tree/master/translations/fa-farsi) |
+[Add translation](https://github.com/satwikkansal/wtfpython/issues/new?title=Add%20translation%20for%20[LANGUAGE]&body=Expected%20time%20to%20finish:%20[X]%20weeks.%20I%27ll%20start%20working%20on%20it%20from%20[Y].)
-Translations: [Chinese 中文](https://github.com/leisurelicht/wtfpython-cn) | [Vietnamese Tiếng Việt](https://github.com/vuduclyunitn/wtfptyhon-vi) | [Spanish Español](https://web.archive.org/web/20220511161045/https://github.com/JoseDeFreitas/wtfpython-es) | [Korean 한국어](https://github.com/buttercrab/wtfpython-ko) | [Russian Русский](https://github.com/satwikkansal/wtfpython/tree/master/translations/ru-russian) | [German Deutsch](https://github.com/BenSt099/wtfpython) | [Add translation](https://github.com/satwikkansal/wtfpython/issues/new?title=Add%20translation%20for%20[LANGUAGE]&body=Expected%20time%20to%20finish:%20[X]%20weeks.%20I%27ll%20start%20working%20on%20it%20from%20[Y].)
+Other modes: [Interactive Website](https://wtfpython-interactive.vercel.app) | [Interactive Notebook](https://colab.research.google.com/github/satwikkansal/wtfpython/blob/master/irrelevant/wtf.ipynb)
-Other modes: [Interactive Website](https://wtfpython-interactive.vercel.app) | [Interactive Notebook](https://colab.research.google.com/github/satwikkansal/wtfpython/blob/master/irrelevant/wtf.ipynb) | [CLI](https://pypi.python.org/pypi/wtfpython)
+Python, being a beautifully designed high-level and interpreter-based programming language,
+provides us with many features for the programmer's comfort.
+But sometimes, the outcomes of a Python snippet may not seem obvious at first sight.
-Python, being a beautifully designed high-level and interpreter-based programming language, provides us with many features for the programmer's comfort. But sometimes, the outcomes of a Python snippet may not seem obvious at first sight.
+Here's a fun project attempting to explain what exactly is happening under the hood for some counter-intuitive snippets
+and lesser-known features in Python.
-Here's a fun project attempting to explain what exactly is happening under the hood for some counter-intuitive snippets and lesser-known features in Python.
+While some of the examples you see below may not be WTFs in the truest sense,
+but they'll reveal some of the interesting parts of Python that you might be unaware of.
+I find it a nice way to learn the internals of a programming language, and I believe that you'll find it interesting too!
-While some of the examples you see below may not be WTFs in the truest sense, but they'll reveal some of the interesting parts of Python that you might be unaware of. I find it a nice way to learn the internals of a programming language, and I believe that you'll find it interesting too!
+If you're an experienced Python programmer, you can take it as a challenge to get most of them right in the first attempt
+You may have already experienced some of them before, and I might be able to revive sweet old memories of yours! :sweat_smile:
-If you're an experienced Python programmer, you can take it as a challenge to get most of them right in the first attempt. You may have already experienced some of them before, and I might be able to revive sweet old memories of yours! :sweat_smile:
-
-PS: If you're a returning reader, you can learn about the new modifications [here](https://github.com/satwikkansal/wtfpython/releases/) (the examples marked with asterisk are the ones added in the latest major revision).
+PS: If you're a returning reader, you can learn about the new modifications [here](https://github.com/satwikkansal/wtfpython/releases/)
+(the examples marked with asterisk are the ones added in the latest major revision).
So, here we go...
@@ -26,83 +46,83 @@ So, here we go...
- [Structure of the Examples](#structure-of-the-examples)
- + [▶ Some fancy Title](#-some-fancy-title)
+ - [▶ Some fancy Title](#-some-fancy-title)
- [Usage](#usage)
- [👀 Examples](#-examples)
- * [Section: Strain your brain!](#section-strain-your-brain)
- + [▶ First things first! *](#-first-things-first-)
- + [▶ Strings can be tricky sometimes](#-strings-can-be-tricky-sometimes)
- + [▶ Be careful with chained operations](#-be-careful-with-chained-operations)
- + [▶ How not to use `is` operator](#-how-not-to-use-is-operator)
- + [▶ Hash brownies](#-hash-brownies)
- + [▶ Deep down, we're all the same.](#-deep-down-were-all-the-same)
- + [▶ Disorder within order *](#-disorder-within-order-)
- + [▶ Keep trying... *](#-keep-trying-)
- + [▶ For what?](#-for-what)
- + [▶ Evaluation time discrepancy](#-evaluation-time-discrepancy)
- + [▶ `is not ...` is not `is (not ...)`](#-is-not--is-not-is-not-)
- + [▶ A tic-tac-toe where X wins in the first attempt!](#-a-tic-tac-toe-where-x-wins-in-the-first-attempt)
- + [▶ Schrödinger's variable](#-schrödingers-variable-)
- + [▶ The chicken-egg problem *](#-the-chicken-egg-problem-)
- + [▶ Subclass relationships](#-subclass-relationships)
- + [▶ Methods equality and identity](#-methods-equality-and-identity)
- + [▶ All-true-ation *](#-all-true-ation-)
- + [▶ The surprising comma](#-the-surprising-comma)
- + [▶ Strings and the backslashes](#-strings-and-the-backslashes)
- + [▶ not knot!](#-not-knot)
- + [▶ Half triple-quoted strings](#-half-triple-quoted-strings)
- + [▶ What's wrong with booleans?](#-whats-wrong-with-booleans)
- + [▶ Class attributes and instance attributes](#-class-attributes-and-instance-attributes)
- + [▶ yielding None](#-yielding-none)
- + [▶ Yielding from... return! *](#-yielding-from-return-)
- + [▶ Nan-reflexivity *](#-nan-reflexivity-)
- + [▶ Mutating the immutable!](#-mutating-the-immutable)
- + [▶ The disappearing variable from outer scope](#-the-disappearing-variable-from-outer-scope)
- + [▶ The mysterious key type conversion](#-the-mysterious-key-type-conversion)
- + [▶ Let's see if you can guess this?](#-lets-see-if-you-can-guess-this)
- + [▶ Exceeds the limit for integer string conversion](#-exceeds-the-limit-for-integer-string-conversion)
- * [Section: Slippery Slopes](#section-slippery-slopes)
- + [▶ Modifying a dictionary while iterating over it](#-modifying-a-dictionary-while-iterating-over-it)
- + [▶ Stubborn `del` operation](#-stubborn-del-operation)
- + [▶ The out of scope variable](#-the-out-of-scope-variable)
- + [▶ Deleting a list item while iterating](#-deleting-a-list-item-while-iterating)
- + [▶ Lossy zip of iterators *](#-lossy-zip-of-iterators-)
- + [▶ Loop variables leaking out!](#-loop-variables-leaking-out)
- + [▶ Beware of default mutable arguments!](#-beware-of-default-mutable-arguments)
- + [▶ Catching the Exceptions](#-catching-the-exceptions)
- + [▶ Same operands, different story!](#-same-operands-different-story)
- + [▶ Name resolution ignoring class scope](#-name-resolution-ignoring-class-scope)
- + [▶ Rounding like a banker *](#-rounding-like-a-banker-)
- + [▶ Needles in a Haystack *](#-needles-in-a-haystack-)
- + [▶ Splitsies *](#-splitsies-)
- + [▶ Wild imports *](#-wild-imports-)
- + [▶ All sorted? *](#-all-sorted-)
- + [▶ Midnight time doesn't exist?](#-midnight-time-doesnt-exist)
- * [Section: The Hidden treasures!](#section-the-hidden-treasures)
- + [▶ Okay Python, Can you make me fly?](#-okay-python-can-you-make-me-fly)
- + [▶ `goto`, but why?](#-goto-but-why)
- + [▶ Brace yourself!](#-brace-yourself)
- + [▶ Let's meet Friendly Language Uncle For Life](#-lets-meet-friendly-language-uncle-for-life)
- + [▶ Even Python understands that love is complicated](#-even-python-understands-that-love-is-complicated)
- + [▶ Yes, it exists!](#-yes-it-exists)
- + [▶ Ellipsis *](#-ellipsis-)
- + [▶ Inpinity](#-inpinity)
- + [▶ Let's mangle](#-lets-mangle)
- * [Section: Appearances are deceptive!](#section-appearances-are-deceptive)
- + [▶ Skipping lines?](#-skipping-lines)
- + [▶ Teleportation](#-teleportation)
- + [▶ Well, something is fishy...](#-well-something-is-fishy)
- * [Section: Miscellaneous](#section-miscellaneous)
- + [▶ `+=` is faster](#--is-faster)
- + [▶ Let's make a giant string!](#-lets-make-a-giant-string)
- + [▶ Slowing down `dict` lookups *](#-slowing-down-dict-lookups-)
- + [▶ Bloating instance `dict`s *](#-bloating-instance-dicts-)
- + [▶ Minor Ones *](#-minor-ones-)
+ - [Section: Strain your brain!](#section-strain-your-brain)
+ - [▶ First things first! \*](#-first-things-first-)
+ - [▶ Strings can be tricky sometimes](#-strings-can-be-tricky-sometimes)
+ - [▶ Be careful with chained operations](#-be-careful-with-chained-operations)
+ - [▶ How not to use `is` operator](#-how-not-to-use-is-operator)
+ - [▶ Hash brownies](#-hash-brownies)
+ - [▶ Deep down, we're all the same.](#-deep-down-were-all-the-same)
+ - [▶ Disorder within order \*](#-disorder-within-order-)
+ - [▶ Keep trying... \*](#-keep-trying-)
+ - [▶ For what?](#-for-what)
+ - [▶ Evaluation time discrepancy](#-evaluation-time-discrepancy)
+ - [▶ `is not ...` is not `is (not ...)`](#-is-not--is-not-is-not-)
+ - [▶ A tic-tac-toe where X wins in the first attempt!](#-a-tic-tac-toe-where-x-wins-in-the-first-attempt)
+ - [▶ Schrödinger's variable](#-schrödingers-variable-)
+ - [▶ The chicken-egg problem \*](#-the-chicken-egg-problem-)
+ - [▶ Subclass relationships](#-subclass-relationships)
+ - [▶ Methods equality and identity](#-methods-equality-and-identity)
+ - [▶ All-true-ation \*](#-all-true-ation-)
+ - [▶ The surprising comma](#-the-surprising-comma)
+ - [▶ Strings and the backslashes](#-strings-and-the-backslashes)
+ - [▶ not knot!](#-not-knot)
+ - [▶ Half triple-quoted strings](#-half-triple-quoted-strings)
+ - [▶ What's wrong with booleans?](#-whats-wrong-with-booleans)
+ - [▶ Class attributes and instance attributes](#-class-attributes-and-instance-attributes)
+ - [▶ yielding None](#-yielding-none)
+ - [▶ Yielding from... return! \*](#-yielding-from-return-)
+ - [▶ Nan-reflexivity \*](#-nan-reflexivity-)
+ - [▶ Mutating the immutable!](#-mutating-the-immutable)
+ - [▶ The disappearing variable from outer scope](#-the-disappearing-variable-from-outer-scope)
+ - [▶ The mysterious key type conversion](#-the-mysterious-key-type-conversion)
+ - [▶ Let's see if you can guess this?](#-lets-see-if-you-can-guess-this)
+ - [▶ Exceeds the limit for integer string conversion](#-exceeds-the-limit-for-integer-string-conversion)
+ - [Section: Slippery Slopes](#section-slippery-slopes)
+ - [▶ Modifying a dictionary while iterating over it](#-modifying-a-dictionary-while-iterating-over-it)
+ - [▶ Stubborn `del` operation](#-stubborn-del-operation)
+ - [▶ The out of scope variable](#-the-out-of-scope-variable)
+ - [▶ Deleting a list item while iterating](#-deleting-a-list-item-while-iterating)
+ - [▶ Lossy zip of iterators \*](#-lossy-zip-of-iterators-)
+ - [▶ Loop variables leaking out!](#-loop-variables-leaking-out)
+ - [▶ Beware of default mutable arguments!](#-beware-of-default-mutable-arguments)
+ - [▶ Catching the Exceptions](#-catching-the-exceptions)
+ - [▶ Same operands, different story!](#-same-operands-different-story)
+ - [▶ Name resolution ignoring class scope](#-name-resolution-ignoring-class-scope)
+ - [▶ Rounding like a banker \*](#-rounding-like-a-banker-)
+ - [▶ Needles in a Haystack \*](#-needles-in-a-haystack-)
+ - [▶ Splitsies \*](#-splitsies-)
+ - [▶ Wild imports \*](#-wild-imports-)
+ - [▶ All sorted? \*](#-all-sorted-)
+ - [▶ Midnight time doesn't exist?](#-midnight-time-doesnt-exist)
+ - [Section: The Hidden treasures!](#section-the-hidden-treasures)
+ - [▶ Okay Python, Can you make me fly?](#-okay-python-can-you-make-me-fly)
+ - [▶ `goto`, but why?](#-goto-but-why)
+ - [▶ Brace yourself!](#-brace-yourself)
+ - [▶ Let's meet Friendly Language Uncle For Life](#-lets-meet-friendly-language-uncle-for-life)
+ - [▶ Even Python understands that love is complicated](#-even-python-understands-that-love-is-complicated)
+ - [▶ Yes, it exists!](#-yes-it-exists)
+ - [▶ Ellipsis \*](#-ellipsis-)
+ - [▶ Inpinity](#-inpinity)
+ - [▶ Let's mangle](#-lets-mangle)
+ - [Section: Appearances are deceptive!](#section-appearances-are-deceptive)
+ - [▶ Skipping lines?](#-skipping-lines)
+ - [▶ Teleportation](#-teleportation)
+ - [▶ Well, something is fishy...](#-well-something-is-fishy)
+ - [Section: Miscellaneous](#section-miscellaneous)
+ - [▶ `+=` is faster](#--is-faster)
+ - [▶ Let's make a giant string!](#-lets-make-a-giant-string)
+ - [▶ Slowing down `dict` lookups \*](#-slowing-down-dict-lookups-)
+ - [▶ Bloating instance `dict`s \*](#-bloating-instance-dicts-)
+ - [▶ Minor Ones \*](#-minor-ones-)
- [Contributing](#contributing)
- [Acknowledgements](#acknowledgements)
- [🎓 License](#-license)
- * [Surprise your friends as well!](#surprise-your-friends-as-well)
- * [More content like this?](#more-content-like-this)
+ - [Surprise your friends as well!](#surprise-your-friends-as-well)
+ - [More content like this?](#more-content-like-this)
@@ -110,6 +130,8 @@ So, here we go...
All the examples are structured like below:
+> ## Section: (if necessary)
+>
> ### ▶ Some fancy Title
>
> ```py
@@ -123,16 +145,18 @@ All the examples are structured like below:
> >>> triggering_statement
> Some unexpected output
> ```
-> (Optional): One line describing the unexpected output.
>
+> (Optional): One line describing the unexpected output.
>
> #### 💡 Explanation:
>
-> * Brief explanation of what's happening and why is it happening.
+> - Brief explanation of what's happening and why is it happening.
+>
> ```py
> # Set up code
> # More examples for further clarification (if necessary)
> ```
+>
> **Output (Python version(s)):**
>
> ```py
@@ -140,33 +164,31 @@ All the examples are structured like below:
> # some justified output
> ```
-**Note:** All the examples are tested on Python 3.5.2 interactive interpreter, and they should work for all the Python versions unless explicitly specified before the output.
+**Note:** All the examples are tested on Python 3.5.2 interactive interpreter,
+and they should work for all the Python versions unless explicitly specified before the output.
# Usage
A nice way to get the most out of these examples, in my opinion, is to read them in sequential order, and for every example:
-- Carefully read the initial code for setting up the example. If you're an experienced Python programmer, you'll successfully anticipate what's going to happen next most of the time.
+
+- Carefully read the initial code for setting up the example.
+ If you're an experienced Python programmer, you'll successfully anticipate what's going to happen next most of the time.
- Read the output snippets and,
- + Check if the outputs are the same as you'd expect.
- + Make sure if you know the exact reason behind the output being the way it is.
- - If the answer is no (which is perfectly okay), take a deep breath, and read the explanation (and if you still don't understand, shout out! and create an issue [here](https://github.com/satwikkansal/wtfpython/issues/new)).
+ - Check if the outputs are the same as you'd expect.
+ - Make sure if you know the exact reason behind the output being the way it is.
+ - If the answer is no (which is perfectly okay), take a deep breath, and read the explanation
+ (and if you still don't understand, shout out! and create an issue [here](https://github.com/satwikkansal/wtfpython/issues/new)).
- If yes, give a gentle pat on your back, and you may skip to the next example.
-PS: You can also read WTFPython at the command line using the [pypi package](https://pypi.python.org/pypi/wtfpython),
-```sh
-$ pip install wtfpython -U
-$ wtfpython
-```
---
# 👀 Examples
## Section: Strain your brain!
-### ▶ First things first! *
+### ▶ First things first! \*
-
For some reason, the Python 3.8's "Walrus" operator (`:=`) has become quite popular. Let's check it out,
@@ -224,13 +246,10 @@ SyntaxError: invalid syntax
16
```
-
-
#### 💡 Explanation
-**Quick walrus operator refresher**
-
-The Walrus operator (`:=`) was introduced in Python 3.8, it can be useful in situations where you'd want to assign values to variables within an expression.
+The Walrus operator (`:=`) was introduced in Python 3.8,
+it can be useful in situations where you'd want to assign values to variables within an expression.
```py
def some_func():
@@ -262,13 +281,14 @@ if a := some_func():
This saved one line of code, and implicitly prevented invoking `some_func` twice.
-- Unparenthesized "assignment expression" (use of walrus operator), is restricted at the top level, hence the `SyntaxError` in the `a := "wtf_walrus"` statement of the first snippet. Parenthesizing it worked as expected and assigned `a`.
-
-- As usual, parenthesizing of an expression containing `=` operator is not allowed. Hence the syntax error in `(a, b = 6, 9)`.
-
-- The syntax of the Walrus operator is of the form `NAME:= expr`, where `NAME` is a valid identifier, and `expr` is a valid expression. Hence, iterable packing and unpacking are not supported which means,
-
- - `(a := 6, 9)` is equivalent to `((a := 6), 9)` and ultimately `(a, 9) ` (where `a`'s value is 6')
+- Unparenthesized "assignment expression" (use of walrus operator), is restricted at the top level,
+ hence the `SyntaxError` in the `a := "wtf_walrus"` statement of the first snippet.
+ Parenthesizing it worked as expected and assigned `a`.
+- As usual, parenthesizing of an expression containing `=` operator is not allowed.
+ Hence the syntax error in `(a, b = 6, 9)`.
+- The syntax of the Walrus operator is of the form `NAME:= expr`, where `NAME` is a valid identifier,
+ and `expr` is a valid expression. Hence, iterable packing and unpacking are not supported which means,
+ - `(a := 6, 9)` is equivalent to `((a := 6), 9)` and ultimately `(a, 9)` (where `a`'s value is 6')
```py
>>> (a := 6, 9) == ((a := 6), 9)
@@ -280,59 +300,44 @@ This saved one line of code, and implicitly prevented invoking `some_func` twice
True
```
- - Similarly, `(a, b := 16, 19)` is equivalent to `(a, (b := 16), 19)` which is nothing but a 3-tuple.
+ - Similarly, `(a, b := 16, 19)` is equivalent to `(a, (b := 16), 19)` which is nothing but a 3-tuple.
---
### ▶ Strings can be tricky sometimes
-1\.
-```py
->>> a = "some_string"
->>> id(a)
-140420665652016
->>> id("some" + "_" + "string") # Notice that both the ids are same.
-140420665652016
-```
-
-2\.
-```py
->>> a = "wtf"
->>> b = "wtf"
->>> a is b
-True
-
->>> a = "wtf!"
->>> b = "wtf!"
->>> a is b
-False
+1\. Notice that both the ids are same.
+```python:snippets/2_tricky_strings.py -s 2 -e 3
+assert id("some_string") == id("some" + "_" + "string")
+assert id("some_string") == id("some_string")
```
-3\.
-
-```py
->>> a, b = "wtf!", "wtf!"
->>> a is b # All versions except 3.7.x
-True
+2\. `True` because it is invoked in script. Might be `False` in `python shell` or `ipython`
->>> a = "wtf!"; b = "wtf!"
->>> a is b # This will print True or False depending on where you're invoking it (python shell / ipython / as a script)
-False
-```
+```python:snippets/2_tricky_strings.py -s 6 -e 12
+a = "wtf"
+b = "wtf"
+assert a is b
-```py
-# This time in file some_file.py
a = "wtf!"
b = "wtf!"
-print(a is b)
+assert a is b
+```
+
+3\. `True` because it is invoked in script. Might be `False` in `python shell` or `ipython`
-# prints True when the module is invoked!
+```python:snippets/2_tricky_strings.py -s 15 -e 19
+a, b = "wtf!", "wtf!"
+assert a is b
+
+a = "wtf!"; b = "wtf!"
+assert a is b
```
-4\.
+4\. **Disclaimer - snippet is not relevant in modern Python versions**
**Output (< Python3.7 )**
@@ -346,23 +351,51 @@ False
Makes sense, right?
#### 💡 Explanation:
-+ The behavior in first and second snippets is due to a CPython optimization (called string interning) that tries to use existing immutable objects in some cases rather than creating a new object every time.
-+ After being "interned," many variables may reference the same string object in memory (saving memory thereby).
-+ In the snippets above, strings are implicitly interned. The decision of when to implicitly intern a string is implementation-dependent. There are some rules that can be used to guess if a string will be interned or not:
- * All length 0 and length 1 strings are interned.
- * Strings are interned at compile time (`'wtf'` will be interned but `''.join(['w', 't', 'f'])` will not be interned)
- * Strings that are not composed of ASCII letters, digits or underscores, are not interned. This explains why `'wtf!'` was not interned due to `!`. CPython implementation of this rule can be found [here](https://github.com/python/cpython/blob/3.6/Objects/codeobject.c#L19)
- 
-+ When `a` and `b` are set to `"wtf!"` in the same line, the Python interpreter creates a new object, then references the second variable at the same time. If you do it on separate lines, it doesn't "know" that there's already `"wtf!"` as an object (because `"wtf!"` is not implicitly interned as per the facts mentioned above). It's a compile-time optimization. This optimization doesn't apply to 3.7.x versions of CPython (check this [issue](https://github.com/satwikkansal/wtfpython/issues/100) for more discussion).
-+ A compile unit in an interactive environment like IPython consists of a single statement, whereas it consists of the entire module in case of modules. `a, b = "wtf!", "wtf!"` is single statement, whereas `a = "wtf!"; b = "wtf!"` are two statements in a single line. This explains why the identities are different in `a = "wtf!"; b = "wtf!"`, and also explain why they are same when invoked in `some_file.py`
-+ The abrupt change in the output of the fourth snippet is due to a [peephole optimization](https://en.wikipedia.org/wiki/Peephole_optimization) technique known as Constant folding. This means the expression `'a'*20` is replaced by `'aaaaaaaaaaaaaaaaaaaa'` during compilation to save a few clock cycles during runtime. Constant folding only occurs for strings having a length of less than 21. (Why? Imagine the size of `.pyc` file generated as a result of the expression `'a'*10**10`). [Here's](https://github.com/python/cpython/blob/3.6/Python/peephole.c#L288) the implementation source for the same.
-+ Note: In Python 3.7, Constant folding was moved out from peephole optimizer to the new AST optimizer with some change in logic as well, so the fourth snippet doesn't work for Python 3.7. You can read more about the change [here](https://bugs.python.org/issue11549).
----
+- The behavior in first and second snippets is due to a CPython optimization (called string interning)
+ that tries to use existing immutable objects in some cases rather than creating a new object every time.
+- After being "interned," many variables may reference the same string object in memory (saving memory thereby).
+- In the snippets above, strings are implicitly interned. The decision of when to implicitly intern a string is
+ implementation-dependent. There are some rules that can be used to guess if a string will be interned or not:
+ - All length 0 and length 1 strings are interned.
+ - Strings are interned at compile time (`'wtf'` will be interned but `''.join(['w', 't', 'f'])` will not be interned)
+ - Strings that are not composed of ASCII letters, digits or underscores, are not interned.
+ This explains why `'wtf!'` was not interned due to `!`. CPython implementation of this rule can be found [here](https://github.com/python/cpython/blob/3.6/Objects/codeobject.c#L19)
+
+
+
+
+
+
+
+
+
+- When `a` and `b` are set to `"wtf!"` in the same line, the Python interpreter creates a new object,
+ then references the second variable at the same time. If you do it on separate lines, it doesn't "know" that
+ there's already `"wtf!"` as an object (because `"wtf!"` is not implicitly interned as per the facts mentioned above).
+ It's a compile-time optimization. This optimization doesn't apply to 3.7.x versions of CPython
+ (check this [issue](https://github.com/satwikkansal/wtfpython/issues/100) for more discussion).
+- A compile unit in an interactive environment like IPython consists of a single statement,
+ whereas it consists of the entire module in case of modules. `a, b = "wtf!", "wtf!"` is single statement,
+ whereas `a = "wtf!"; b = "wtf!"` are two statements in a single line.
+ This explains why the identities are different in `a = "wtf!"; b = "wtf!"`,
+ and also explain why they are same when invoked in `some_file.py`
+- The abrupt change in the output of the fourth snippet is due to a
+ [peephole optimization](https://en.wikipedia.org/wiki/Peephole_optimization) technique known as Constant folding.
+ This means the expression `'a'*20` is replaced by `'aaaaaaaaaaaaaaaaaaaa'` during compilation to save
+ a few clock cycles during runtime. Constant folding only occurs for strings having a length of less than 21.
+ (Why? Imagine the size of `.pyc` file generated as a result of the expression `'a'*10**10`).
+ [Here's](https://github.com/python/cpython/blob/3.6/Python/peephole.c#L288) the implementation source for the same.
+- Note: In Python 3.7, Constant folding was moved out from peephole optimizer to the new AST optimizer
+ with some change in logic as well, so the fourth snippet doesn't work for Python 3.7.
+ You can read more about the change [here](https://bugs.python.org/issue11549).
+---
### ▶ Be careful with chained operations
+
+
```py
>>> (False == False) in [False] # makes sense
False
@@ -388,26 +421,34 @@ False
As per https://docs.python.org/3/reference/expressions.html#comparisons
-> Formally, if a, b, c, ..., y, z are expressions and op1, op2, ..., opN are comparison operators, then a op1 b op2 c ... y opN z is equivalent to a op1 b and b op2 c and ... y opN z, except that each expression is evaluated at most once.
+> Formally, if a, b, c, ..., y, z are expressions and op1, op2, ..., opN are comparison operators,
+ then a op1 b op2 c ... y opN z is equivalent to a op1 b and b op2 c and ... y opN z,
+ except that each expression is evaluated at most once.
+
+While such behavior might seem silly to you in the above examples,
+it's fantastic with stuff like `a == b == c` and `0 <= x <= 100`.
-While such behavior might seem silly to you in the above examples, it's fantastic with stuff like `a == b == c` and `0 <= x <= 100`.
+- `False is False is False` is equivalent to `(False is False) and (False is False)`
+- `True is False == False` is equivalent to `(True is False) and (False == False)`
+ and since the first part of the statement (`True is False`) evaluates to `False`, the overall expression evaluates to `False`.
+- `1 > 0 < 1` is equivalent to `(1 > 0) and (0 < 1)` which evaluates to `True`.
+- The expression `(1 > 0) < 1` is equivalent to `True < 1` and
-* `False is False is False` is equivalent to `(False is False) and (False is False)`
-* `True is False == False` is equivalent to `(True is False) and (False == False)` and since the first part of the statement (`True is False`) evaluates to `False`, the overall expression evaluates to `False`.
-* `1 > 0 < 1` is equivalent to `(1 > 0) and (0 < 1)` which evaluates to `True`.
-* The expression `(1 > 0) < 1` is equivalent to `True < 1` and
```py
>>> int(True)
1
- >>> True + 1 #not relevant for this example, but just for fun
+ >>> True + 1 # not relevant for this example, but just for fun
2
```
+
So, `1 < 1` evaluates to `False`
---
### ▶ How not to use `is` operator
+
+
The following is a very famous example present all over the internet.
1\.
@@ -459,9 +500,10 @@ False
**The difference between `is` and `==`**
-* `is` operator checks if both the operands refer to the same object (i.e., it checks if the identity of the operands matches or not).
-* `==` operator compares the values of both the operands and checks if they are the same.
-* So `is` is for reference equality and `==` is for value equality. An example to clear things up,
+- `is` operator checks if both the operands refer to the same object (i.e., it checks if the identity of the operands matches or not).
+- `==` operator compares the values of both the operands and checks if they are the same.
+- So `is` is for reference equality and `==` is for value equality. An example to clear things up,
+
```py
>>> class A: pass
>>> A() is A() # These are two empty objects at two different memory locations.
@@ -473,6 +515,7 @@ False
When you start up python the numbers from `-5` to `256` will be allocated. These numbers are used a lot, so it makes sense just to have them ready.
Quoting from https://docs.python.org/3/c-api/long.html
+
> The current implementation keeps an array of integer objects for all integers between -5 and 256, when you create an int in that range you just get back a reference to the existing object. So it should be possible to change the value of 1. I suspect the behavior of Python, in this case, is undefined. :-)
```py
@@ -496,7 +539,7 @@ Quoting from https://docs.python.org/3/c-api/long.html
Here the interpreter isn't smart enough while executing `y = 257` to recognize that we've already created an integer of the value `257,` and so it goes on to create another object in the memory.
-Similar optimization applies to other **immutable** objects like empty tuples as well. Since lists are mutable, that's why `[] is []` will return `False` and `() is ()` will return `True`. This explains our second snippet. Let's move on to the third one,
+Similar optimization applies to other **immutable** objects like empty tuples as well. Since lists are mutable, that's why `[] is []` will return `False` and `() is ()` will return `True`. This explains our second snippet. Let's move on to the third one,
**Both `a` and `b` refer to the same object when initialized with same value in the same line.**
@@ -516,9 +559,9 @@ Similar optimization applies to other **immutable** objects like empty tuples as
140640774013488
```
-* When a and b are set to `257` in the same line, the Python interpreter creates a new object, then references the second variable at the same time. If you do it on separate lines, it doesn't "know" that there's already `257` as an object.
+- When a and b are set to `257` in the same line, the Python interpreter creates a new object, then references the second variable at the same time. If you do it on separate lines, it doesn't "know" that there's already `257` as an object.
-* It's a compiler optimization and specifically applies to the interactive environment. When you enter two lines in a live interpreter, they're compiled separately, therefore optimized separately. If you were to try this example in a `.py` file, you would not see the same behavior, because the file is compiled all at once. This optimization is not limited to integers, it works for other immutable data types like strings (check the "Strings are tricky example") and floats as well,
+- It's a compiler optimization and specifically applies to the interactive environment. When you enter two lines in a live interpreter, they're compiled separately, therefore optimized separately. If you were to try this example in a `.py` file, you would not see the same behavior, because the file is compiled all at once. This optimization is not limited to integers, it works for other immutable data types like strings (check the "Strings are tricky example") and floats as well,
```py
>>> a, b = 257.0, 257.0
@@ -526,14 +569,16 @@ Similar optimization applies to other **immutable** objects like empty tuples as
True
```
-* Why didn't this work for Python 3.7? The abstract reason is because such compiler optimizations are implementation specific (i.e. may change with version, OS, etc). I'm still figuring out what exact implementation change cause the issue, you can check out this [issue](https://github.com/satwikkansal/wtfpython/issues/100) for updates.
+- Why didn't this work for Python 3.7? The abstract reason is because such compiler optimizations are implementation specific (i.e. may change with version, OS, etc). I'm still figuring out what exact implementation change cause the issue, you can check out this [issue](https://github.com/satwikkansal/wtfpython/issues/100) for updates.
---
-
### ▶ Hash brownies
+
+
1\.
+
```py
some_dict = {}
some_dict[5.5] = "JavaScript"
@@ -548,7 +593,7 @@ some_dict[5] = "Python"
"JavaScript"
>>> some_dict[5.0] # "Python" destroyed the existence of "Ruby"?
"Python"
->>> some_dict[5]
+>>> some_dict[5]
"Python"
>>> complex_five = 5 + 0j
@@ -560,10 +605,10 @@ complex
So, why is Python all over the place?
-
#### 💡 Explanation
-* Uniqueness of keys in a Python dictionary is by *equivalence*, not identity. So even though `5`, `5.0`, and `5 + 0j` are distinct objects of different types, since they're equal, they can't both be in the same `dict` (or `set`). As soon as you insert any one of them, attempting to look up any distinct but equivalent key will succeed with the original mapped value (rather than failing with a `KeyError`):
+- Uniqueness of keys in a Python dictionary is by _equivalence_, not identity. So even though `5`, `5.0`, and `5 + 0j` are distinct objects of different types, since they're equal, they can't both be in the same `dict` (or `set`). As soon as you insert any one of them, attempting to look up any distinct but equivalent key will succeed with the original mapped value (rather than failing with a `KeyError`):
+
```py
>>> 5 == 5.0 == 5 + 0j
True
@@ -576,7 +621,9 @@ So, why is Python all over the place?
>>> (5 in some_dict) and (5 + 0j in some_dict)
True
```
-* This applies when setting an item as well. So when you do `some_dict[5] = "Python"`, Python finds the existing item with equivalent key `5.0 -> "Ruby"`, overwrites its value in place, and leaves the original key alone.
+
+- This applies when setting an item as well. So when you do `some_dict[5] = "Python"`, Python finds the existing item with equivalent key `5.0 -> "Ruby"`, overwrites its value in place, and leaves the original key alone.
+
```py
>>> some_dict
{5.0: 'Ruby'}
@@ -584,27 +631,33 @@ So, why is Python all over the place?
>>> some_dict
{5.0: 'Python'}
```
-* So how can we update the key to `5` (instead of `5.0`)? We can't actually do this update in place, but what we can do is first delete the key (`del some_dict[5.0]`), and then set it (`some_dict[5]`) to get the integer `5` as the key instead of floating `5.0`, though this should be needed in rare cases.
-* How did Python find `5` in a dictionary containing `5.0`? Python does this in constant time without having to scan through every item by using hash functions. When Python looks up a key `foo` in a dict, it first computes `hash(foo)` (which runs in constant-time). Since in Python it is required that objects that compare equal also have the same hash value ([docs](https://docs.python.org/3/reference/datamodel.html#object.__hash__) here), `5`, `5.0`, and `5 + 0j` have the same hash value.
+- So how can we update the key to `5` (instead of `5.0`)? We can't actually do this update in place, but what we can do is first delete the key (`del some_dict[5.0]`), and then set it (`some_dict[5]`) to get the integer `5` as the key instead of floating `5.0`, though this should be needed in rare cases.
+
+- How did Python find `5` in a dictionary containing `5.0`? Python does this in constant time without having to scan through every item by using hash functions. When Python looks up a key `foo` in a dict, it first computes `hash(foo)` (which runs in constant-time). Since in Python it is required that objects that compare equal also have the same hash value ([docs](https://docs.python.org/3/reference/datamodel.html#object.__hash__) here), `5`, `5.0`, and `5 + 0j` have the same hash value.
+
```py
>>> 5 == 5.0 == 5 + 0j
True
>>> hash(5) == hash(5.0) == hash(5 + 0j)
True
```
- **Note:** The inverse is not necessarily true: Objects with equal hash values may themselves be unequal. (This causes what's known as a [hash collision](https://en.wikipedia.org/wiki/Collision_(computer_science)), and degrades the constant-time performance that hashing usually provides.)
+
+ **Note:** The inverse is not necessarily true: Objects with equal hash values may themselves be unequal. (This causes what's known as a [hash collision](), and degrades the constant-time performance that hashing usually provides.)
---
### ▶ Deep down, we're all the same.
+
+
```py
class WTF:
pass
```
**Output:**
+
```py
>>> WTF() == WTF() # two different instances can't be equal
False
@@ -618,10 +671,11 @@ True
#### 💡 Explanation:
-* When `id` was called, Python created a `WTF` class object and passed it to the `id` function. The `id` function takes its `id` (its memory location), and throws away the object. The object is destroyed.
-* When we do this twice in succession, Python allocates the same memory location to this second object as well. Since (in CPython) `id` uses the memory location as the object id, the id of the two objects is the same.
-* So, the object's id is unique only for the lifetime of the object. After the object is destroyed, or before it is created, something else can have the same id.
-* But why did the `is` operator evaluate to `False`? Let's see with this snippet.
+- When `id` was called, Python created a `WTF` class object and passed it to the `id` function. The `id` function takes its `id` (its memory location), and throws away the object. The object is destroyed.
+- When we do this twice in succession, Python allocates the same memory location to this second object as well. Since (in CPython) `id` uses the memory location as the object id, the id of the two objects is the same.
+- So, the object's id is unique only for the lifetime of the object. After the object is destroyed, or before it is created, something else can have the same id.
+- But why did the `is` operator evaluate to `False`? Let's see with this snippet.
+
```py
class WTF(object):
def __init__(self): print("I")
@@ -629,6 +683,7 @@ True
```
**Output:**
+
```py
>>> WTF() is WTF()
I
@@ -643,12 +698,15 @@ True
D
True
```
+
As you may observe, the order in which the objects are destroyed is what made all the difference here.
---
-### ▶ Disorder within order *
+### ▶ Disorder within order \*
+
+
```py
from collections import OrderedDict
@@ -675,6 +733,7 @@ class OrderedDictWithHash(OrderedDict):
```
**Output**
+
```py
>>> dictionary == ordered_dict # If a == b
True
@@ -710,43 +769,48 @@ What is going on here?
#### 💡 Explanation:
- The reason why intransitive equality didn't hold among `dictionary`, `ordered_dict` and `another_ordered_dict` is because of the way `__eq__` method is implemented in `OrderedDict` class. From the [docs](https://docs.python.org/3/library/collections.html#ordereddict-objects)
-
- > Equality tests between OrderedDict objects are order-sensitive and are implemented as `list(od1.items())==list(od2.items())`. Equality tests between `OrderedDict` objects and other Mapping objects are order-insensitive like regular dictionaries.
+
+ > Equality tests between OrderedDict objects are order-sensitive and are implemented as `list(od1.items())==list(od2.items())`. Equality tests between `OrderedDict` objects and other Mapping objects are order-insensitive like regular dictionaries.
+
- The reason for this equality in behavior is that it allows `OrderedDict` objects to be directly substituted anywhere a regular dictionary is used.
- Okay, so why did changing the order affect the length of the generated `set` object? The answer is the lack of intransitive equality only. Since sets are "unordered" collections of unique elements, the order in which elements are inserted shouldn't matter. But in this case, it does matter. Let's break it down a bit,
- ```py
- >>> some_set = set()
- >>> some_set.add(dictionary) # these are the mapping objects from the snippets above
- >>> ordered_dict in some_set
- True
- >>> some_set.add(ordered_dict)
- >>> len(some_set)
- 1
- >>> another_ordered_dict in some_set
- True
- >>> some_set.add(another_ordered_dict)
- >>> len(some_set)
- 1
-
- >>> another_set = set()
- >>> another_set.add(ordered_dict)
- >>> another_ordered_dict in another_set
- False
- >>> another_set.add(another_ordered_dict)
- >>> len(another_set)
- 2
- >>> dictionary in another_set
- True
- >>> another_set.add(another_ordered_dict)
- >>> len(another_set)
- 2
- ```
- So the inconsistency is due to `another_ordered_dict in another_set` being `False` because `ordered_dict` was already present in `another_set` and as observed before, `ordered_dict == another_ordered_dict` is `False`.
+
+ ```py
+ >>> some_set = set()
+ >>> some_set.add(dictionary) # these are the mapping objects from the snippets above
+ >>> ordered_dict in some_set
+ True
+ >>> some_set.add(ordered_dict)
+ >>> len(some_set)
+ 1
+ >>> another_ordered_dict in some_set
+ True
+ >>> some_set.add(another_ordered_dict)
+ >>> len(some_set)
+ 1
+
+ >>> another_set = set()
+ >>> another_set.add(ordered_dict)
+ >>> another_ordered_dict in another_set
+ False
+ >>> another_set.add(another_ordered_dict)
+ >>> len(another_set)
+ 2
+ >>> dictionary in another_set
+ True
+ >>> another_set.add(another_ordered_dict)
+ >>> len(another_set)
+ 2
+ ```
+
+ So the inconsistency is due to `another_ordered_dict in another_set` being `False` because `ordered_dict` was already present in `another_set` and as observed before, `ordered_dict == another_ordered_dict` is `False`.
---
-### ▶ Keep trying... *
+### ▶ Keep trying... \*
+
+
```py
def some_func():
try:
@@ -754,7 +818,7 @@ def some_func():
finally:
return 'from_finally'
-def another_func():
+def another_func():
for _ in range(3):
try:
continue
@@ -805,9 +869,10 @@ Iteration 0
---
-
### ▶ For what?
+
+
```py
some_string = "wtf"
some_dict = {}
@@ -816,19 +881,23 @@ for i, some_dict[i] in enumerate(some_string):
```
**Output:**
+
```py
>>> some_dict # An indexed dict appears.
{0: 'w', 1: 't', 2: 'f'}
```
-#### 💡 Explanation:
+#### 💡 Explanation:
+
+- A `for` statement is defined in the [Python grammar](https://docs.python.org/3/reference/grammar.html) as:
-* A `for` statement is defined in the [Python grammar](https://docs.python.org/3/reference/grammar.html) as:
```
for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite]
```
+
Where `exprlist` is the assignment target. This means that the equivalent of `{exprlist} = {next_value}` is **executed for each item** in the iterable.
An interesting example that illustrates this:
+
```py
for i in range(4):
print(i)
@@ -836,6 +905,7 @@ for i, some_dict[i] in enumerate(some_string):
```
**Output:**
+
```
0
1
@@ -849,7 +919,8 @@ for i, some_dict[i] in enumerate(some_string):
- The assignment statement `i = 10` never affects the iterations of the loop because of the way for loops work in Python. Before the beginning of every iteration, the next item provided by the iterator (`range(4)` in this case) is unpacked and assigned the target list variables (`i` in this case).
-* The `enumerate(some_string)` function yields a new value `i` (a counter going up) and a character from the `some_string` in each iteration. It then sets the (just assigned) `i` key of the dictionary `some_dict` to that character. The unrolling of the loop can be simplified as:
+- The `enumerate(some_string)` function yields a new value `i` (a counter going up) and a character from the `some_string` in each iteration. It then sets the (just assigned) `i` key of the dictionary `some_dict` to that character. The unrolling of the loop can be simplified as:
+
```py
>>> i, some_dict[i] = (0, 'w')
>>> i, some_dict[i] = (1, 't')
@@ -860,8 +931,11 @@ for i, some_dict[i] in enumerate(some_string):
---
### ▶ Evaluation time discrepancy
+
+
1\.
+
```py
array = [1, 8, 15]
# A typical generator expression
@@ -889,6 +963,7 @@ array_2[:] = [1,2,3,4,5]
```
**Output:**
+
```py
>>> print(list(gen_1))
[1, 2, 3, 4]
@@ -909,6 +984,7 @@ array_4 = [400, 500, 600]
```
**Output:**
+
```py
>>> print(list(gen))
[401, 501, 601, 402, 502, 602, 403, 503, 603]
@@ -922,14 +998,15 @@ array_4 = [400, 500, 600]
- In the first case, `array_1` is bound to the new object `[1,2,3,4,5]` and since the `in` clause is evaluated at the declaration time it still refers to the old object `[1,2,3,4]` (which is not destroyed).
- In the second case, the slice assignment to `array_2` updates the same old object `[1,2,3,4]` to `[1,2,3,4,5]`. Hence both the `g2` and `array_2` still have reference to the same object (which has now been updated to `[1,2,3,4,5]`).
- Okay, going by the logic discussed so far, shouldn't be the value of `list(gen)` in the third snippet be `[11, 21, 31, 12, 22, 32, 13, 23, 33]`? (because `array_3` and `array_4` are going to behave just like `array_1`). The reason why (only) `array_4` values got updated is explained in [PEP-289](https://www.python.org/dev/peps/pep-0289/#the-details)
-
- > Only the outermost for-expression is evaluated immediately, the other expressions are deferred until the generator is run.
----
+ > Only the outermost for-expression is evaluated immediately, the other expressions are deferred until the generator is run.
+---
### ▶ `is not ...` is not `is (not ...)`
+
+
```py
>>> 'something' is not None
True
@@ -940,12 +1017,13 @@ False
#### 💡 Explanation
- `is not` is a single binary operator, and has behavior different than using `is` and `not` separated.
-- `is not` evaluates to `False` if the variables on either side of the operator point to the same object and `True` otherwise.
+- `is not` evaluates to `False` if the variables on either side of the operator point to the same object and `True` otherwise.
- In the example, `(not None)` evaluates to `True` since the value `None` is `False` in a boolean context, so the expression becomes `'something' is True`.
---
### ▶ A tic-tac-toe where X wins in the first attempt!
+
```py
@@ -975,11 +1053,23 @@ We didn't assign three `"X"`s, did we?
When we initialize `row` variable, this visualization explains what happens in the memory
-
+
+
+
+
+
+
+
And when the `board` is initialized by multiplying the `row`, this is what happens inside the memory (each of the elements `board[0]`, `board[1]` and `board[2]` is a reference to the same list referred by `row`)
-
+
+
+
+
+
+
+
We can avoid this scenario here by not using `row` variable to generate `board`. (Asked in [this](https://github.com/satwikkansal/wtfpython/issues/68) issue).
@@ -992,9 +1082,9 @@ We can avoid this scenario here by not using `row` variable to generate `board`.
---
-### ▶ Schrödinger's variable *
-
+### ▶ Schrödinger's variable \*
+
```py
funcs = []
@@ -1009,6 +1099,7 @@ funcs_results = [func() for func in funcs]
```
**Output (Python version):**
+
```py
>>> results
[0, 1, 2, 3, 4, 5, 6]
@@ -1027,12 +1118,19 @@ The values of `x` were different in every iteration prior to appending `some_fun
```
#### 💡 Explanation:
-* When defining a function inside a loop that uses the loop variable in its body, the loop function's closure is bound to the *variable*, not its *value*. The function looks up `x` in the surrounding context, rather than using the value of `x` at the time the function is created. So all of the functions use the latest value assigned to the variable for computation. We can see that it's using the `x` from the surrounding context (i.e. *not* a local variable) with:
+
+- When defining a function inside a loop that uses the loop variable in its body,
+ the loop function's closure is bound to the _variable_, not its _value_.
+ The function looks up `x` in the surrounding context, rather than using the value of `x` at the time
+ the function is created. So all of the functions use the latest value assigned to the variable for computation.
+ We can see that it's using the `x` from the surrounding context (i.e. _not_ a local variable) with:
+
```py
>>> import inspect
>>> inspect.getclosurevars(funcs[0])
ClosureVars(nonlocals={}, globals={'x': 6}, builtins={}, unbound=set())
```
+
Since `x` is a global value, we can change the value that the `funcs` will lookup and return by updating `x`:
```py
@@ -1041,7 +1139,7 @@ Since `x` is a global value, we can change the value that the `funcs` will looku
[42, 42, 42, 42, 42, 42, 42]
```
-* To get the desired behavior you can pass in the loop variable as a named variable to the function. **Why does this work?** Because this will define the variable *inside* the function's scope. It will no longer go to the surrounding (global) scope to look up the variables value but will create a local variable that stores the value of `x` at that point in time.
+- To get the desired behavior you can pass in the loop variable as a named variable to the function. **Why does this work?** Because this will define the variable _inside_ the function's scope. It will no longer go to the surrounding (global) scope to look up the variables value but will create a local variable that stores the value of `x` at that point in time.
```py
funcs = []
@@ -1068,9 +1166,12 @@ ClosureVars(nonlocals={}, globals={}, builtins={}, unbound=set())
---
-### ▶ The chicken-egg problem *
+### ▶ The chicken-egg problem \*
+
+
1\.
+
```py
>>> isinstance(3, int)
True
@@ -1082,7 +1183,7 @@ True
So which is the "ultimate" base class? There's more to the confusion by the way,
-2\.
+2\.
```py
>>> class A: pass
@@ -1105,22 +1206,24 @@ True
False
```
-
#### 💡 Explanation
- `type` is a [metaclass](https://realpython.com/python-metaclasses/) in Python.
- **Everything** is an `object` in Python, which includes classes as well as their objects (instances).
- class `type` is the metaclass of class `object`, and every class (including `type`) has inherited directly or indirectly from `object`.
- There is no real base class among `object` and `type`. The confusion in the above snippets is arising because we're thinking about these relationships (`issubclass` and `isinstance`) in terms of Python classes. The relationship between `object` and `type` can't be reproduced in pure python. To be more precise the following relationships can't be reproduced in pure Python,
- + class A is an instance of class B, and class B is an instance of class A.
- + class A is an instance of itself.
+ - class A is an instance of class B, and class B is an instance of class A.
+ - class A is an instance of itself.
- These relationships between `object` and `type` (both being instances of each other as well as themselves) exist in Python because of "cheating" at the implementation level.
---
### ▶ Subclass relationships
+
+
**Output:**
+
```py
>>> from collections.abc import Hashable
>>> issubclass(list, object)
@@ -1135,17 +1238,19 @@ The Subclass relationships were expected to be transitive, right? (i.e., if `A`
#### 💡 Explanation:
-* Subclass relationships are not necessarily transitive in Python. Anyone is allowed to define their own, arbitrary `__subclasscheck__` in a metaclass.
-* When `issubclass(cls, Hashable)` is called, it simply looks for non-Falsey "`__hash__`" method in `cls` or anything it inherits from.
-* Since `object` is hashable, but `list` is non-hashable, it breaks the transitivity relation.
-* More detailed explanation can be found [here](https://www.naftaliharris.com/blog/python-subclass-intransitivity/).
+- Subclass relationships are not necessarily transitive in Python. Anyone is allowed to define their own, arbitrary `__subclasscheck__` in a metaclass.
+- When `issubclass(cls, Hashable)` is called, it simply looks for non-Falsey "`__hash__`" method in `cls` or anything it inherits from.
+- Since `object` is hashable, but `list` is non-hashable, it breaks the transitivity relation.
+- More detailed explanation can be found [here](https://www.naftaliharris.com/blog/python-subclass-intransitivity/).
---
### ▶ Methods equality and identity
+
1.
+
```py
class SomeClass:
def method(self):
@@ -1161,6 +1266,7 @@ class SomeClass:
```
**Output:**
+
```py
>>> print(SomeClass.method is SomeClass.method)
True
@@ -1172,16 +1278,18 @@ True
True
```
-Accessing `classm` twice, we get an equal object, but not the *same* one? Let's see what happens
+Accessing `classm` twice, we get an equal object, but not the _same_ one? Let's see what happens
with instances of `SomeClass`:
2.
+
```py
o1 = SomeClass()
o2 = SomeClass()
```
**Output:**
+
```py
>>> print(o1.method == o2.method)
False
@@ -1197,53 +1305,64 @@ True
True
```
-Accessing `classm` or `method` twice, creates equal but not *same* objects for the same instance of `SomeClass`.
+Accessing `classm` or `method` twice, creates equal but not _same_ objects for the same instance of `SomeClass`.
#### 💡 Explanation
-* Functions are [descriptors](https://docs.python.org/3/howto/descriptor.html). Whenever a function is accessed as an
-attribute, the descriptor is invoked, creating a method object which "binds" the function with the object owning the
-attribute. If called, the method calls the function, implicitly passing the bound object as the first argument
-(this is how we get `self` as the first argument, despite not passing it explicitly).
+
+- Functions are [descriptors](https://docs.python.org/3/howto/descriptor.html). Whenever a function is accessed as an
+ attribute, the descriptor is invoked, creating a method object which "binds" the function with the object owning the
+ attribute. If called, the method calls the function, implicitly passing the bound object as the first argument
+ (this is how we get `self` as the first argument, despite not passing it explicitly).
+
```py
>>> o1.method
>
```
-* Accessing the attribute multiple times creates a method object every time! Therefore `o1.method is o1.method` is
-never truthy. Accessing functions as class attributes (as opposed to instance) does not create methods, however; so
-`SomeClass.method is SomeClass.method` is truthy.
+
+- Accessing the attribute multiple times creates a method object every time! Therefore `o1.method is o1.method` is
+ never truthy. Accessing functions as class attributes (as opposed to instance) does not create methods, however; so
+ `SomeClass.method is SomeClass.method` is truthy.
+
```py
>>> SomeClass.method
```
-* `classmethod` transforms functions into class methods. Class methods are descriptors that, when accessed, create
-a method object which binds the *class* (type) of the object, instead of the object itself.
+
+- `classmethod` transforms functions into class methods. Class methods are descriptors that, when accessed, create
+ a method object which binds the _class_ (type) of the object, instead of the object itself.
+
```py
>>> o1.classm
>
```
-* Unlike functions, `classmethod`s will create a method also when accessed as class attributes (in which case they
-bind the class, not to the type of it). So `SomeClass.classm is SomeClass.classm` is falsy.
+
+- Unlike functions, `classmethod`s will create a method also when accessed as class attributes (in which case they
+ bind the class, not to the type of it). So `SomeClass.classm is SomeClass.classm` is falsy.
+
```py
>>> SomeClass.classm
>
```
-* A method object compares equal when both the functions are equal, and the bound objects are the same. So
-`o1.method == o1.method` is truthy, although not the same object in memory.
-* `staticmethod` transforms functions into a "no-op" descriptor, which returns the function as-is. No method
-objects are ever created, so comparison with `is` is truthy.
+
+- A method object compares equal when both the functions are equal, and the bound objects are the same. So
+ `o1.method == o1.method` is truthy, although not the same object in memory.
+- `staticmethod` transforms functions into a "no-op" descriptor, which returns the function as-is. No method
+ objects are ever created, so comparison with `is` is truthy.
+
```py
>>> o1.staticm
>>> SomeClass.staticm
```
-* Having to create new "method" objects every time Python calls instance methods and having to modify the arguments
+
+- Having to create new "method" objects every time Python calls instance methods and having to modify the arguments
every time in order to insert `self` affected performance badly.
CPython 3.7 [solved it](https://bugs.python.org/issue26110) by introducing new opcodes that deal with calling methods
without creating the temporary method objects. This is used only when the accessed function is actually called, so the
snippets here are not affected, and still generate methods :)
-### ▶ All-true-ation *
+### ▶ All-true-ation \*
@@ -1275,14 +1394,16 @@ Why's this True-False alteration?
return True
```
-- `all([])` returns `True` since the iterable is empty.
+- `all([])` returns `True` since the iterable is empty.
- `all([[]])` returns `False` because the passed array has one element, `[]`, and in python, an empty list is falsy.
- `all([[[]]])` and higher recursive variants are always `True`. This is because the passed array's single element (`[[...]]`) is no longer empty, and lists with values are truthy.
---
### ▶ The surprising comma
+
+
**Output (< 3.6):**
```py
@@ -1308,14 +1429,17 @@ SyntaxError: invalid syntax
#### 💡 Explanation:
- Trailing comma is not always legal in formal parameters list of a Python function.
-- In Python, the argument list is defined partially with leading commas and partially with trailing commas. This conflict causes situations where a comma is trapped in the middle, and no rule accepts it.
-- **Note:** The trailing comma problem is [fixed in Python 3.6](https://bugs.python.org/issue9232). The remarks in [this](https://bugs.python.org/issue9232#msg248399) post discuss in brief different usages of trailing commas in Python.
+- In Python, the argument list is defined partially with leading commas and partially with trailing commas. This conflict causes situations where a comma is trapped in the middle, and no rule accepts it.
+- **Note:** The trailing comma problem is [fixed in Python 3.6](https://bugs.python.org/issue9232). The remarks in [this](https://bugs.python.org/issue9232#msg248399) post discuss in brief different usages of trailing commas in Python.
---
### ▶ Strings and the backslashes
+
+
**Output:**
+
```py
>>> print("\"")
"
@@ -1336,34 +1460,41 @@ True
#### 💡 Explanation
- In a usual python string, the backslash is used to escape characters that may have a special meaning (like single-quote, double-quote, and the backslash itself).
- ```py
- >>> "wt\"f"
- 'wt"f'
- ```
-- In a raw string literal (as indicated by the prefix `r`), the backslashes pass themselves as is along with the behavior of escaping the following character.
- ```py
- >>> r'wt\"f' == 'wt\\"f'
- True
- >>> print(repr(r'wt\"f')
- 'wt\\"f'
- >>> print("\n")
+ ```py
+ >>> "wt\"f"
+ 'wt"f'
+ ```
+
+- In a raw string literal (as indicated by the prefix `r`), the backslashes pass themselves as is along with the behavior of escaping the following character.
+
+ ```py
+ >>> r'wt\"f' == 'wt\\"f'
+ True
+ >>> print(repr(r'wt\"f'))
+ 'wt\\"f'
+
+ >>> print("\n")
+
+ >>> print(r"\\n")
+ '\\n'
+ ```
- >>> print(r"\\n")
- '\\n'
- ```
- This means when a parser encounters a backslash in a raw string, it expects another character following it. And in our case (`print(r"\")`), the backslash escaped the trailing quote, leaving the parser without a terminating quote (hence the `SyntaxError`). That's why backslashes don't work at the end of a raw string.
---
### ▶ not knot!
+
+
```py
x = True
y = False
```
**Output:**
+
```py
>>> not x == y
True
@@ -1376,16 +1507,19 @@ SyntaxError: invalid syntax
#### 💡 Explanation:
-* Operator precedence affects how an expression is evaluated, and `==` operator has higher precedence than `not` operator in Python.
-* So `not x == y` is equivalent to `not (x == y)` which is equivalent to `not (True == False)` finally evaluating to `True`.
-* But `x == not y` raises a `SyntaxError` because it can be thought of being equivalent to `(x == not) y` and not `x == (not y)` which you might have expected at first sight.
-* The parser expected the `not` token to be a part of the `not in` operator (because both `==` and `not in` operators have the same precedence), but after not being able to find an `in` token following the `not` token, it raises a `SyntaxError`.
+- Operator precedence affects how an expression is evaluated, and `==` operator has higher precedence than `not` operator in Python.
+- So `not x == y` is equivalent to `not (x == y)` which is equivalent to `not (True == False)` finally evaluating to `True`.
+- But `x == not y` raises a `SyntaxError` because it can be thought of being equivalent to `(x == not) y` and not `x == (not y)` which you might have expected at first sight.
+- The parser expected the `not` token to be a part of the `not in` operator (because both `==` and `not in` operators have the same precedence), but after not being able to find an `in` token following the `not` token, it raises a `SyntaxError`.
---
### ▶ Half triple-quoted strings
+
+
**Output:**
+
```py
>>> print('wtfpython''')
wtfpython
@@ -1401,19 +1535,24 @@ SyntaxError: EOF while scanning triple-quoted string literal
```
#### 💡 Explanation:
-+ Python supports implicit [string literal concatenation](https://docs.python.org/3/reference/lexical_analysis.html#string-literal-concatenation), Example,
+
+- Python supports implicit [string literal concatenation](https://docs.python.org/3/reference/lexical_analysis.html#string-literal-concatenation), Example,
+
```
>>> print("wtf" "python")
wtfpython
>>> print("wtf" "") # or "wtf"""
wtf
```
-+ `'''` and `"""` are also string delimiters in Python which causes a SyntaxError because the Python interpreter was expecting a terminating triple quote as delimiter while scanning the currently encountered triple quoted string literal.
+
+- `'''` and `"""` are also string delimiters in Python which causes a SyntaxError because the Python interpreter was expecting a terminating triple quote as delimiter while scanning the currently encountered triple quoted string literal.
---
### ▶ What's wrong with booleans?
+
+
1\.
```py
@@ -1431,6 +1570,7 @@ for item in mixed_list:
```
**Output:**
+
```py
>>> integers_found_so_far
4
@@ -1438,8 +1578,8 @@ for item in mixed_list:
0
```
-
2\.
+
```py
>>> some_bool = True
>>> "wtf" * some_bool
@@ -1465,20 +1605,19 @@ def tell_truth():
I have lost faith in truth!
```
+#### 💡 Explanation:
+- `bool` is a subclass of `int` in Python
-#### 💡 Explanation:
+ ```py
+ >>> issubclass(bool, int)
+ True
+ >>> issubclass(int, bool)
+ False
+ ```
+
+- And thus, `True` and `False` are instances of `int`
-* `bool` is a subclass of `int` in Python
-
- ```py
- >>> issubclass(bool, int)
- True
- >>> issubclass(int, bool)
- False
- ```
-
-* And thus, `True` and `False` are instances of `int`
```py
>>> isinstance(True, int)
True
@@ -1486,7 +1625,8 @@ I have lost faith in truth!
True
```
-* The integer value of `True` is `1` and that of `False` is `0`.
+- The integer value of `True` is `1` and that of `False` is `0`.
+
```py
>>> int(True)
1
@@ -1494,17 +1634,20 @@ I have lost faith in truth!
0
```
-* See this StackOverflow [answer](https://stackoverflow.com/a/8169049/4354153) for the rationale behind it.
+- See this StackOverflow [answer](https://stackoverflow.com/a/8169049/4354153) for the rationale behind it.
-* Initially, Python used to have no `bool` type (people used 0 for false and non-zero value like 1 for true). `True`, `False`, and a `bool` type was added in 2.x versions, but, for backward compatibility, `True` and `False` couldn't be made constants. They just were built-in variables, and it was possible to reassign them
+- Initially, Python used to have no `bool` type (people used 0 for false and non-zero value like 1 for true). `True`, `False`, and a `bool` type was added in 2.x versions, but, for backward compatibility, `True` and `False` couldn't be made constants. They just were built-in variables, and it was possible to reassign them
-* Python 3 was backward-incompatible, the issue was finally fixed, and thus the last snippet won't work with Python 3.x!
+- Python 3 was backward-incompatible, the issue was finally fixed, and thus the last snippet won't work with Python 3.x!
---
### ▶ Class attributes and instance attributes
+
+
1\.
+
```py
class A:
x = 1
@@ -1517,6 +1660,7 @@ class C(A):
```
**Output:**
+
```py
>>> A.x, B.x, C.x
(1, 1, 1)
@@ -1535,6 +1679,7 @@ class C(A):
```
2\.
+
```py
class SomeClass:
some_var = 15
@@ -1567,13 +1712,15 @@ True
#### 💡 Explanation:
-* Class variables and variables in class instances are internally handled as dictionaries of a class object. If a variable name is not found in the dictionary of the current class, the parent classes are searched for it.
-* The `+=` operator modifies the mutable object in-place without creating a new object. So changing the attribute of one instance affects the other instances and the class attribute as well.
+- Class variables and variables in class instances are internally handled as dictionaries of a class object. If a variable name is not found in the dictionary of the current class, the parent classes are searched for it.
+- The `+=` operator modifies the mutable object in-place without creating a new object. So changing the attribute of one instance affects the other instances and the class attribute as well.
---
### ▶ yielding None
+
+
```py
some_iterable = ('a', 'b')
@@ -1597,6 +1744,7 @@ def some_func(val):
```
#### 💡 Explanation:
+
- This is a bug in CPython's handling of `yield` in generators and comprehensions.
- Source and explanation can be found here: https://stackoverflow.com/questions/32139885/yield-in-list-comprehensions-and-generator-expressions
- Related bug report: https://bugs.python.org/issue10544
@@ -1604,9 +1752,10 @@ def some_func(val):
---
+### ▶ Yielding from... return! \*
-### ▶ Yielding from... return! *
+
1\.
```py
@@ -1648,13 +1797,13 @@ The same result, this didn't work either.
#### 💡 Explanation:
-+ From Python 3.3 onwards, it became possible to use `return` statement with values inside generators (See [PEP380](https://www.python.org/dev/peps/pep-0380/)). The [official docs](https://www.python.org/dev/peps/pep-0380/#enhancements-to-stopiteration) say that,
+- From Python 3.3 onwards, it became possible to use `return` statement with values inside generators (See [PEP380](https://www.python.org/dev/peps/pep-0380/)). The [official docs](https://www.python.org/dev/peps/pep-0380/#enhancements-to-stopiteration) say that,
> "... `return expr` in a generator causes `StopIteration(expr)` to be raised upon exit from the generator."
-+ In the case of `some_func(3)`, `StopIteration` is raised at the beginning because of `return` statement. The `StopIteration` exception is automatically caught inside the `list(...)` wrapper and the `for` loop. Therefore, the above two snippets result in an empty list.
+- In the case of `some_func(3)`, `StopIteration` is raised at the beginning because of `return` statement. The `StopIteration` exception is automatically caught inside the `list(...)` wrapper and the `for` loop. Therefore, the above two snippets result in an empty list.
-+ To get `["wtf"]` from the generator `some_func` we need to catch the `StopIteration` exception,
+- To get `["wtf"]` from the generator `some_func` we need to catch the `StopIteration` exception,
```py
try:
@@ -1670,7 +1819,7 @@ The same result, this didn't work either.
---
-### ▶ Nan-reflexivity *
+### ▶ Nan-reflexivity \*
@@ -1721,13 +1870,11 @@ False
True
```
-
-
#### 💡 Explanation:
- `'inf'` and `'nan'` are special strings (case-insensitive), which, when explicitly typecast-ed to `float` type, are used to represent mathematical "infinity" and "not a number" respectively.
-- Since according to IEEE standards ` NaN != NaN`, obeying this rule breaks the reflexivity assumption of a collection element in Python i.e. if `x` is a part of a collection like `list`, the implementations like comparison are based on the assumption that `x == x`. Because of this assumption, the identity is compared first (since it's faster) while comparing two elements, and the values are compared only when the identities mismatch. The following snippet will make things clearer,
+- Since according to IEEE standards `NaN != NaN`, obeying this rule breaks the reflexivity assumption of a collection element in Python i.e. if `x` is a part of a collection like `list`, the implementations like comparison are based on the assumption that `x == x`. Because of this assumption, the identity is compared first (since it's faster) while comparing two elements, and the values are compared only when the identities mismatch. The following snippet will make things clearer,
```py
>>> x = float('nan')
@@ -1758,6 +1905,7 @@ another_tuple = ([1, 2], [3, 4], [5, 6])
```
**Output:**
+
```py
>>> some_tuple[2] = "change this"
TypeError: 'tuple' object does not support item assignment
@@ -1774,17 +1922,19 @@ But I thought tuples were immutable...
#### 💡 Explanation:
-* Quoting from https://docs.python.org/3/reference/datamodel.html
+- Quoting from https://docs.python.org/3/reference/datamodel.html
+
+ > Immutable sequences
- > Immutable sequences
An object of an immutable sequence type cannot change once it is created. (If the object contains references to other objects, these other objects may be mutable and may be modified; however, the collection of objects directly referenced by an immutable object cannot change.)
-* `+=` operator changes the list in-place. The item assignment doesn't work, but when the exception occurs, the item has already been changed in place.
-* There's also an explanation in [official Python FAQ](https://docs.python.org/3/faq/programming.html#why-does-a-tuple-i-item-raise-an-exception-when-the-addition-works).
+- `+=` operator changes the list in-place. The item assignment doesn't work, but when the exception occurs, the item has already been changed in place.
+- There's also an explanation in [official Python FAQ](https://docs.python.org/3/faq/programming.html#why-does-a-tuple-i-item-raise-an-exception-when-the-addition-works).
---
### ▶ The disappearing variable from outer scope
+
```py
@@ -1796,12 +1946,14 @@ except Exception as e:
```
**Output (Python 2.x):**
+
```py
>>> print(e)
# prints nothing
```
**Output (Python 3.x):**
+
```py
>>> print(e)
NameError: name 'e' is not defined
@@ -1809,7 +1961,7 @@ NameError: name 'e' is not defined
#### 💡 Explanation:
-* Source: https://docs.python.org/3/reference/compound_stmts.html#except
+- Source: https://docs.python.org/3/reference/compound_stmts.html#except
When an exception has been assigned using `as` target, it is cleared at the end of the `except` clause. This is as if
@@ -1830,44 +1982,47 @@ NameError: name 'e' is not defined
This means the exception must be assigned to a different name to be able to refer to it after the except clause. Exceptions are cleared because, with the traceback attached to them, they form a reference cycle with the stack frame, keeping all locals in that frame alive until the next garbage collection occurs.
-* The clauses are not scoped in Python. Everything in the example is present in the same scope, and the variable `e` got removed due to the execution of the `except` clause. The same is not the case with functions that have their separate inner-scopes. The example below illustrates this:
+- The clauses are not scoped in Python. Everything in the example is present in the same scope, and the variable `e` got removed due to the execution of the `except` clause. The same is not the case with functions that have their separate inner-scopes. The example below illustrates this:
- ```py
- def f(x):
- del(x)
- print(x)
+ ```py
+ def f(x):
+ del(x)
+ print(x)
- x = 5
- y = [5, 4, 3]
- ```
+ x = 5
+ y = [5, 4, 3]
+ ```
- **Output:**
- ```py
- >>> f(x)
- UnboundLocalError: local variable 'x' referenced before assignment
- >>> f(y)
- UnboundLocalError: local variable 'x' referenced before assignment
- >>> x
- 5
- >>> y
- [5, 4, 3]
- ```
+ **Output:**
-* In Python 2.x, the variable name `e` gets assigned to `Exception()` instance, so when you try to print, it prints nothing.
+ ```py
+ >>> f(x)
+ UnboundLocalError: local variable 'x' referenced before assignment
+ >>> f(y)
+ UnboundLocalError: local variable 'x' referenced before assignment
+ >>> x
+ 5
+ >>> y
+ [5, 4, 3]
+ ```
- **Output (Python 2.x):**
- ```py
- >>> e
- Exception()
- >>> print e
- # Nothing is printed!
- ```
+- In Python 2.x, the variable name `e` gets assigned to `Exception()` instance, so when you try to print, it prints nothing.
----
+ **Output (Python 2.x):**
+
+ ```py
+ >>> e
+ Exception()
+ >>> print e
+ # Nothing is printed!
+ ```
+---
### ▶ The mysterious key type conversion
+
+
```py
class SomeClass(str):
pass
@@ -1876,6 +2031,7 @@ some_dict = {'s': 42}
```
**Output:**
+
```py
>>> type(list(some_dict.keys())[0])
str
@@ -1889,10 +2045,11 @@ str
#### 💡 Explanation:
-* Both the object `s` and the string `"s"` hash to the same value because `SomeClass` inherits the `__hash__` method of `str` class.
-* `SomeClass("s") == "s"` evaluates to `True` because `SomeClass` also inherits `__eq__` method from `str` class.
-* Since both the objects hash to the same value and are equal, they are represented by the same key in the dictionary.
-* For the desired behavior, we can redefine the `__eq__` method in `SomeClass`
+- Both the object `s` and the string `"s"` hash to the same value because `SomeClass` inherits the `__hash__` method of `str` class.
+- `SomeClass("s") == "s"` evaluates to `True` because `SomeClass` also inherits `__eq__` method from `str` class.
+- Since both the objects hash to the same value and are equal, they are represented by the same key in the dictionary.
+- For the desired behavior, we can redefine the `__eq__` method in `SomeClass`
+
```py
class SomeClass(str):
def __eq__(self, other):
@@ -1910,6 +2067,7 @@ str
```
**Output:**
+
```py
>>> s = SomeClass('s')
>>> some_dict[s] = 40
@@ -1923,12 +2081,15 @@ str
---
### ▶ Let's see if you can guess this?
+
+
```py
a, b = a[b] = {}, 5
```
**Output:**
+
```py
>>> a
{5: ({...}, 5)}
@@ -1936,23 +2097,26 @@ a, b = a[b] = {}, 5
#### 💡 Explanation:
-* According to [Python language reference](https://docs.python.org/3/reference/simple_stmts.html#assignment-statements), assignment statements have the form
+- According to [Python language reference](https://docs.python.org/3/reference/simple_stmts.html#assignment-statements), assignment statements have the form
+
```
(target_list "=")+ (expression_list | yield_expression)
```
+
and
-
+
> An assignment statement evaluates the expression list (remember that this can be a single expression or a comma-separated list, the latter yielding a tuple) and assigns the single resulting object to each of the target lists, from left to right.
-* The `+` in `(target_list "=")+` means there can be **one or more** target lists. In this case, target lists are `a, b` and `a[b]` (note the expression list is exactly one, which in our case is `{}, 5`).
+- The `+` in `(target_list "=")+` means there can be **one or more** target lists. In this case, target lists are `a, b` and `a[b]` (note the expression list is exactly one, which in our case is `{}, 5`).
-* After the expression list is evaluated, its value is unpacked to the target lists from **left to right**. So, in our case, first the `{}, 5` tuple is unpacked to `a, b` and we now have `a = {}` and `b = 5`.
+- After the expression list is evaluated, its value is unpacked to the target lists from **left to right**. So, in our case, first the `{}, 5` tuple is unpacked to `a, b` and we now have `a = {}` and `b = 5`.
-* `a` is now assigned to `{}`, which is a mutable object.
+- `a` is now assigned to `{}`, which is a mutable object.
-* The second target list is `a[b]` (you may expect this to throw an error because both `a` and `b` have not been defined in the statements before. But remember, we just assigned `a` to `{}` and `b` to `5`).
+- The second target list is `a[b]` (you may expect this to throw an error because both `a` and `b` have not been defined in the statements before. But remember, we just assigned `a` to `{}` and `b` to `5`).
+
+- Now, we are setting the key `5` in the dictionary to the tuple `({}, 5)` creating a circular reference (the `{...}` in the output refers to the same object that `a` is already referencing). Another simpler example of circular reference could be
-* Now, we are setting the key `5` in the dictionary to the tuple `({}, 5)` creating a circular reference (the `{...}` in the output refers to the same object that `a` is already referencing). Another simpler example of circular reference could be
```py
>>> some_list = some_list[0] = [0]
>>> some_list
@@ -1964,23 +2128,27 @@ a, b = a[b] = {}, 5
>>> some_list[0][0][0][0][0][0] == some_list
True
```
+
Similar is the case in our example (`a[b][0]` is the same object as `a`)
-* So to sum it up, you can break the example down to
+- So to sum it up, you can break the example down to
+
```py
a, b = {}, 5
a[b] = a, b
```
+
And the circular reference can be justified by the fact that `a[b][0]` is the same object as `a`
+
```py
>>> a[b][0] is a
True
```
-
---
### ▶ Exceeds the limit for integer string conversion
+
```py
>>> # Python 3.10.6
>>> int("2" * 5432)
@@ -1990,6 +2158,7 @@ a, b = a[b] = {}, 5
```
**Output:**
+
```py
>>> # Python 3.10.6
222222222222222222222222222222222222222222222222222222222222222...
@@ -2003,23 +2172,25 @@ ValueError: Exceeds the limit (4300) for integer string conversion:
```
#### 💡 Explanation:
+
This call to `int()` works fine in Python 3.10.6 and raises a ValueError in Python 3.10.8. Note that Python can still work with large integers. The error is only raised when converting between integers and strings.
Fortunately, you can increase the limit for the allowed number of digits when you expect an operation to exceed it. To do this, you can use one of the following:
+
- The -X int_max_str_digits command-line flag
- The set_int_max_str_digits() function from the sys module
- The PYTHONINTMAXSTRDIGITS environment variable
[Check the documentation](https://docs.python.org/3/library/stdtypes.html#int-max-str-digits) for more details on changing the default limit if you expect your code to exceed this value.
-
---
-
## Section: Slippery Slopes
### ▶ Modifying a dictionary while iterating over it
+
+
```py
x = {0: None}
@@ -2046,15 +2217,16 @@ Yes, it runs for exactly **eight** times and stops.
#### 💡 Explanation:
-* Iteration over a dictionary that you edit at the same time is not supported.
-* It runs eight times because that's the point at which the dictionary resizes to hold more keys (we have eight deletion entries, so a resize is needed). This is actually an implementation detail.
-* How deleted keys are handled and when the resize occurs might be different for different Python implementations.
-* So for Python versions other than Python 2.7 - Python 3.5, the count might be different from 8 (but whatever the count is, it's going to be the same every time you run it). You can find some discussion around this [here](https://github.com/satwikkansal/wtfpython/issues/53) or in [this](https://stackoverflow.com/questions/44763802/bug-in-python-dict) StackOverflow thread.
-* Python 3.7.6 onwards, you'll see `RuntimeError: dictionary keys changed during iteration` exception if you try to do this.
+- Iteration over a dictionary that you edit at the same time is not supported.
+- It runs eight times because that's the point at which the dictionary resizes to hold more keys (we have eight deletion entries, so a resize is needed). This is actually an implementation detail.
+- How deleted keys are handled and when the resize occurs might be different for different Python implementations.
+- So for Python versions other than Python 2.7 - Python 3.5, the count might be different from 8 (but whatever the count is, it's going to be the same every time you run it). You can find some discussion around this [here](https://github.com/satwikkansal/wtfpython/issues/53) or in [this](https://stackoverflow.com/questions/44763802/bug-in-python-dict) StackOverflow thread.
+- Python 3.7.6 onwards, you'll see `RuntimeError: dictionary keys changed during iteration` exception if you try to do this.
---
### ▶ Stubborn `del` operation
+
@@ -2066,6 +2238,7 @@ class SomeClass:
**Output:**
1\.
+
```py
>>> x = SomeClass()
>>> y = x
@@ -2077,6 +2250,7 @@ Deleted!
Phew, deleted at last. You might have guessed what saved `__del__` from being called in our first attempt to delete `x`. Let's add more twists to the example.
2\.
+
```py
>>> x = SomeClass()
>>> y = x
@@ -2092,17 +2266,20 @@ Deleted!
Okay, now it's deleted :confused:
#### 💡 Explanation:
-+ `del x` doesn’t directly call `x.__del__()`.
-+ When `del x` is encountered, Python deletes the name `x` from current scope and decrements by 1 the reference count of the object `x` referenced. `__del__()` is called only when the object's reference count reaches zero.
-+ In the second output snippet, `__del__()` was not called because the previous statement (`>>> y`) in the interactive interpreter created another reference to the same object (specifically, the `_` magic variable which references the result value of the last non `None` expression on the REPL), thus preventing the reference count from reaching zero when `del y` was encountered.
-+ Calling `globals` (or really, executing anything that will have a non `None` result) caused `_` to reference the new result, dropping the existing reference. Now the reference count reached 0 and we can see "Deleted!" being printed (finally!).
+
+- `del x` doesn’t directly call `x.__del__()`.
+- When `del x` is encountered, Python deletes the name `x` from current scope and decrements by 1 the reference count of the object `x` referenced. `__del__()` is called only when the object's reference count reaches zero.
+- In the second output snippet, `__del__()` was not called because the previous statement (`>>> y`) in the interactive interpreter created another reference to the same object (specifically, the `_` magic variable which references the result value of the last non `None` expression on the REPL), thus preventing the reference count from reaching zero when `del y` was encountered.
+- Calling `globals` (or really, executing anything that will have a non `None` result) caused `_` to reference the new result, dropping the existing reference. Now the reference count reached 0 and we can see "Deleted!" being printed (finally!).
---
### ▶ The out of scope variable
+
1\.
+
```py
a = 1
def some_func():
@@ -2114,6 +2291,7 @@ def another_func():
```
2\.
+
```py
def some_closure_func():
a = 1
@@ -2130,6 +2308,7 @@ def another_closure_func():
```
**Output:**
+
```py
>>> some_func()
1
@@ -2143,8 +2322,10 @@ UnboundLocalError: local variable 'a' referenced before assignment
```
#### 💡 Explanation:
-* When you make an assignment to a variable in scope, it becomes local to that scope. So `a` becomes local to the scope of `another_func`, but it has not been initialized previously in the same scope, which throws an error.
-* To modify the outer scope variable `a` in `another_func`, we have to use the `global` keyword.
+
+- When you make an assignment to a variable in scope, it becomes local to that scope. So `a` becomes local to the scope of `another_func`, but it has not been initialized previously in the same scope, which throws an error.
+- To modify the outer scope variable `a` in `another_func`, we have to use the `global` keyword.
+
```py
def another_func()
global a
@@ -2153,12 +2334,15 @@ UnboundLocalError: local variable 'a' referenced before assignment
```
**Output:**
+
```py
>>> another_func()
2
```
-* In `another_closure_func`, `a` becomes local to the scope of `another_inner_func`, but it has not been initialized previously in the same scope, which is why it throws an error.
-* To modify the outer scope variable `a` in `another_inner_func`, use the `nonlocal` keyword. The nonlocal statement is used to refer to variables defined in the nearest outer (excluding the global) scope.
+
+- In `another_closure_func`, `a` becomes local to the scope of `another_inner_func`, but it has not been initialized previously in the same scope, which is why it throws an error.
+- To modify the outer scope variable `a` in `another_inner_func`, use the `nonlocal` keyword. The nonlocal statement is used to refer to variables defined in the nearest outer (excluding the global) scope.
+
```py
def another_func():
a = 1
@@ -2170,17 +2354,21 @@ UnboundLocalError: local variable 'a' referenced before assignment
```
**Output:**
+
```py
>>> another_func()
2
```
-* The keywords `global` and `nonlocal` tell the python interpreter to not declare new variables and look them up in the corresponding outer scopes.
-* Read [this](https://sebastianraschka.com/Articles/2014_python_scope_and_namespaces.html) short but an awesome guide to learn more about how namespaces and scope resolution works in Python.
+
+- The keywords `global` and `nonlocal` tell the python interpreter to not declare new variables and look them up in the corresponding outer scopes.
+- Read [this](https://sebastianraschka.com/Articles/2014_python_scope_and_namespaces.html) short but an awesome guide to learn more about how namespaces and scope resolution works in Python.
---
### ▶ Deleting a list item while iterating
+
+
```py
list_1 = [1, 2, 3, 4]
list_2 = [1, 2, 3, 4]
@@ -2201,6 +2389,7 @@ for idx, item in enumerate(list_4):
```
**Output:**
+
```py
>>> list_1
[1, 2, 3, 4]
@@ -2216,31 +2405,33 @@ Can you guess why the output is `[2, 4]`?
#### 💡 Explanation:
-* It's never a good idea to change the object you're iterating over. The correct way to do so is to iterate over a copy of the object instead, and `list_3[:]` does just that.
+- It's never a good idea to change the object you're iterating over. The correct way to do so is to iterate over a copy of the object instead, and `list_3[:]` does just that.
- ```py
- >>> some_list = [1, 2, 3, 4]
- >>> id(some_list)
- 139798789457608
- >>> id(some_list[:]) # Notice that python creates new object for sliced list.
- 139798779601192
- ```
+ ```py
+ >>> some_list = [1, 2, 3, 4]
+ >>> id(some_list)
+ 139798789457608
+ >>> id(some_list[:]) # Notice that python creates new object for sliced list.
+ 139798779601192
+ ```
**Difference between `del`, `remove`, and `pop`:**
-* `del var_name` just removes the binding of the `var_name` from the local or global namespace (That's why the `list_1` is unaffected).
-* `remove` removes the first matching value, not a specific index, raises `ValueError` if the value is not found.
-* `pop` removes the element at a specific index and returns it, raises `IndexError` if an invalid index is specified.
+
+- `del var_name` just removes the binding of the `var_name` from the local or global namespace (That's why the `list_1` is unaffected).
+- `remove` removes the first matching value, not a specific index, raises `ValueError` if the value is not found.
+- `pop` removes the element at a specific index and returns it, raises `IndexError` if an invalid index is specified.
**Why the output is `[2, 4]`?**
+
- The list iteration is done index by index, and when we remove `1` from `list_2` or `list_4`, the contents of the lists are now `[2, 3, 4]`. The remaining elements are shifted down, i.e., `2` is at index 0, and `3` is at index 1. Since the next iteration is going to look at index 1 (which is the `3`), the `2` gets skipped entirely. A similar thing will happen with every alternate element in the list sequence.
-* Refer to this StackOverflow [thread](https://stackoverflow.com/questions/45946228/what-happens-when-you-try-to-delete-a-list-element-while-iterating-over-it) explaining the example
-* See also this nice StackOverflow [thread](https://stackoverflow.com/questions/45877614/how-to-change-all-the-dictionary-keys-in-a-for-loop-with-d-items) for a similar example related to dictionaries in Python.
+- Refer to this StackOverflow [thread](https://stackoverflow.com/questions/45946228/what-happens-when-you-try-to-delete-a-list-element-while-iterating-over-it) explaining the example
+- See also this nice StackOverflow [thread](https://stackoverflow.com/questions/45877614/how-to-change-all-the-dictionary-keys-in-a-for-loop-with-d-items) for a similar example related to dictionaries in Python.
---
+### ▶ Lossy zip of iterators \*
-### ▶ Lossy zip of iterators *
```py
@@ -2251,47 +2442,55 @@ Can you guess why the output is `[2, 4]`?
>>> first_three, remaining
([0, 1, 2], [3, 4, 5, 6])
>>> numbers_iter = iter(numbers)
->>> list(zip(numbers_iter, first_three))
+>>> list(zip(numbers_iter, first_three))
[(0, 0), (1, 1), (2, 2)]
# so far so good, let's zip the remaining
>>> list(zip(numbers_iter, remaining))
[(4, 3), (5, 4), (6, 5)]
```
+
Where did element `3` go from the `numbers` list?
#### 💡 Explanation:
- From Python [docs](https://docs.python.org/3.3/library/functions.html#zip), here's an approximate implementation of zip function,
- ```py
- def zip(*iterables):
- sentinel = object()
- iterators = [iter(it) for it in iterables]
- while iterators:
- result = []
- for it in iterators:
- elem = next(it, sentinel)
- if elem is sentinel: return
- result.append(elem)
- yield tuple(result)
- ```
-- So the function takes in arbitrary number of iterable objects, adds each of their items to the `result` list by calling the `next` function on them, and stops whenever any of the iterable is exhausted.
+
+ ```py
+ def zip(*iterables):
+ sentinel = object()
+ iterators = [iter(it) for it in iterables]
+ while iterators:
+ result = []
+ for it in iterators:
+ elem = next(it, sentinel)
+ if elem is sentinel: return
+ result.append(elem)
+ yield tuple(result)
+ ```
+
+- So the function takes in arbitrary number of iterable objects, adds each of their items to the `result` list by calling the `next` function on them, and stops whenever any of the iterable is exhausted.
- The caveat here is when any iterable is exhausted, the existing elements in the `result` list are discarded. That's what happened with `3` in the `numbers_iter`.
- The correct way to do the above using `zip` would be,
- ```py
- >>> numbers = list(range(7))
- >>> numbers_iter = iter(numbers)
- >>> list(zip(first_three, numbers_iter))
- [(0, 0), (1, 1), (2, 2)]
- >>> list(zip(remaining, numbers_iter))
- [(3, 3), (4, 4), (5, 5), (6, 6)]
- ```
- The first argument of zip should be the one with fewest elements.
+
+ ```py
+ >>> numbers = list(range(7))
+ >>> numbers_iter = iter(numbers)
+ >>> list(zip(first_three, numbers_iter))
+ [(0, 0), (1, 1), (2, 2)]
+ >>> list(zip(remaining, numbers_iter))
+ [(3, 3), (4, 4), (5, 5), (6, 6)]
+ ```
+
+ The first argument of zip should be the one with fewest elements.
---
### ▶ Loop variables leaking out!
+
+
1\.
+
```py
for x in range(7):
if x == 6:
@@ -2300,6 +2499,7 @@ print(x, ': x in global')
```
**Output:**
+
```py
6 : for x inside loop
6 : x in global
@@ -2308,6 +2508,7 @@ print(x, ': x in global')
But `x` was never defined outside the scope of for loop...
2\.
+
```py
# This time let's initialize x first
x = -1
@@ -2318,6 +2519,7 @@ print(x, ': x in global')
```
**Output:**
+
```py
6 : for x inside loop
6 : x in global
@@ -2326,6 +2528,7 @@ print(x, ': x in global')
3\.
**Output (Python 2.x):**
+
```py
>>> x = 1
>>> print([x for x in range(5)])
@@ -2335,6 +2538,7 @@ print(x, ': x in global')
```
**Output (Python 3.x):**
+
```py
>>> x = 1
>>> print([x for x in range(5)])
@@ -2349,11 +2553,12 @@ print(x, ': x in global')
- The differences in the output of Python 2.x and Python 3.x interpreters for list comprehension example can be explained by following change documented in [What’s New In Python 3.0](https://docs.python.org/3/whatsnew/3.0.html) changelog:
- > "List comprehensions no longer support the syntactic form `[... for var in item1, item2, ...]`. Use `[... for var in (item1, item2, ...)]` instead. Also, note that list comprehensions have different semantics: they are closer to syntactic sugar for a generator expression inside a `list()` constructor, and in particular, the loop control variables are no longer leaked into the surrounding scope."
+ > "List comprehensions no longer support the syntactic form `[... for var in item1, item2, ...]`. Use `[... for var in (item1, item2, ...)]` instead. Also, note that list comprehensions have different semantics: they are closer to syntactic sugar for a generator expression inside a `list()` constructor, and in particular, the loop control variables are no longer leaked into the surrounding scope."
---
### ▶ Beware of default mutable arguments!
+
```py
@@ -2363,6 +2568,7 @@ def some_func(default_arg=[]):
```
**Output:**
+
```py
>>> some_func()
['some_string']
@@ -2378,41 +2584,44 @@ def some_func(default_arg=[]):
- The default mutable arguments of functions in Python aren't really initialized every time you call the function. Instead, the recently assigned value to them is used as the default value. When we explicitly passed `[]` to `some_func` as the argument, the default value of the `default_arg` variable was not used, so the function returned as expected.
- ```py
- def some_func(default_arg=[]):
- default_arg.append("some_string")
- return default_arg
- ```
+ ```py
+ def some_func(default_arg=[]):
+ default_arg.append("some_string")
+ return default_arg
+ ```
- **Output:**
- ```py
- >>> some_func.__defaults__ #This will show the default argument values for the function
- ([],)
- >>> some_func()
- >>> some_func.__defaults__
- (['some_string'],)
- >>> some_func()
- >>> some_func.__defaults__
- (['some_string', 'some_string'],)
- >>> some_func([])
- >>> some_func.__defaults__
- (['some_string', 'some_string'],)
- ```
+ **Output:**
+
+ ```py
+ >>> some_func.__defaults__ #This will show the default argument values for the function
+ ([],)
+ >>> some_func()
+ >>> some_func.__defaults__
+ (['some_string'],)
+ >>> some_func()
+ >>> some_func.__defaults__
+ (['some_string', 'some_string'],)
+ >>> some_func([])
+ >>> some_func.__defaults__
+ (['some_string', 'some_string'],)
+ ```
- A common practice to avoid bugs due to mutable arguments is to assign `None` as the default value and later check if any value is passed to the function corresponding to that argument. Example:
- ```py
- def some_func(default_arg=None):
- if default_arg is None:
- default_arg = []
- default_arg.append("some_string")
- return default_arg
- ```
+ ```py
+ def some_func(default_arg=None):
+ if default_arg is None:
+ default_arg = []
+ default_arg.append("some_string")
+ return default_arg
+ ```
---
### ▶ Catching the Exceptions
+
+
```py
some_list = [1, 2, 3]
try:
@@ -2429,6 +2638,7 @@ except IndexError, ValueError:
```
**Output (Python 2.x):**
+
```py
Caught!
@@ -2436,6 +2646,7 @@ ValueError: list.remove(x): x not in list
```
**Output (Python 3.x):**
+
```py
File "", line 3
except IndexError, ValueError:
@@ -2445,7 +2656,8 @@ SyntaxError: invalid syntax
#### 💡 Explanation
-* To add multiple Exceptions to the except clause, you need to pass them as parenthesized tuple as the first argument. The second argument is an optional name, which when supplied will bind the Exception instance that has been raised. Example,
+- To add multiple Exceptions to the except clause, you need to pass them as parenthesized tuple as the first argument. The second argument is an optional name, which when supplied will bind the Exception instance that has been raised. Example,
+
```py
some_list = [1, 2, 3]
try:
@@ -2455,12 +2667,16 @@ SyntaxError: invalid syntax
print("Caught again!")
print(e)
```
+
**Output (Python 2.x):**
+
```
Caught again!
list.remove(x): x not in list
```
+
**Output (Python 3.x):**
+
```py
File "", line 4
except (IndexError, ValueError), e:
@@ -2468,7 +2684,8 @@ SyntaxError: invalid syntax
IndentationError: unindent does not match any outer indentation level
```
-* Separating the exception from the variable with a comma is deprecated and does not work in Python 3; the correct way is to use `as`. Example,
+- Separating the exception from the variable with a comma is deprecated and does not work in Python 3; the correct way is to use `as`. Example,
+
```py
some_list = [1, 2, 3]
try:
@@ -2478,7 +2695,9 @@ SyntaxError: invalid syntax
print("Caught again!")
print(e)
```
+
**Output:**
+
```
Caught again!
list.remove(x): x not in list
@@ -2487,8 +2706,11 @@ SyntaxError: invalid syntax
---
### ▶ Same operands, different story!
+
+
1\.
+
```py
a = [1, 2, 3, 4]
b = a
@@ -2496,6 +2718,7 @@ a = a + [5, 6, 7, 8]
```
**Output:**
+
```py
>>> a
[1, 2, 3, 4, 5, 6, 7, 8]
@@ -2504,6 +2727,7 @@ a = a + [5, 6, 7, 8]
```
2\.
+
```py
a = [1, 2, 3, 4]
b = a
@@ -2511,6 +2735,7 @@ a += [5, 6, 7, 8]
```
**Output:**
+
```py
>>> a
[1, 2, 3, 4, 5, 6, 7, 8]
@@ -2520,17 +2745,20 @@ a += [5, 6, 7, 8]
#### 💡 Explanation:
-* `a += b` doesn't always behave the same way as `a = a + b`. Classes *may* implement the *`op=`* operators differently, and lists do this.
+- `a += b` doesn't always behave the same way as `a = a + b`. Classes _may_ implement the _`op=`_ operators differently, and lists do this.
-* The expression `a = a + [5,6,7,8]` generates a new list and sets `a`'s reference to that new list, leaving `b` unchanged.
+- The expression `a = a + [5,6,7,8]` generates a new list and sets `a`'s reference to that new list, leaving `b` unchanged.
-* The expression `a += [5,6,7,8]` is actually mapped to an "extend" function that operates on the list such that `a` and `b` still point to the same list that has been modified in-place.
+- The expression `a += [5,6,7,8]` is actually mapped to an "extend" function that operates on the list such that `a` and `b` still point to the same list that has been modified in-place.
---
### ▶ Name resolution ignoring class scope
+
+
1\.
+
```py
x = 5
class SomeClass:
@@ -2539,12 +2767,14 @@ class SomeClass:
```
**Output:**
+
```py
>>> list(SomeClass.y)[0]
5
```
2\.
+
```py
x = 5
class SomeClass:
@@ -2553,27 +2783,31 @@ class SomeClass:
```
**Output (Python 2.x):**
+
```py
>>> SomeClass.y[0]
17
```
**Output (Python 3.x):**
+
```py
>>> SomeClass.y[0]
5
```
#### 💡 Explanation
+
- Scopes nested inside class definition ignore names bound at the class level.
- A generator expression has its own scope.
- Starting from Python 3.X, list comprehensions also have their own scope.
---
-### ▶ Rounding like a banker *
+### ▶ Rounding like a banker \*
Let's implement a naive function to get the middle element of a list:
+
```py
def get_middle(some_list):
mid_index = round(len(some_list) / 2)
@@ -2581,6 +2815,7 @@ def get_middle(some_list):
```
**Python 3.x:**
+
```py
>>> get_middle([1]) # looks good
1
@@ -2593,6 +2828,7 @@ def get_middle(some_list):
>>> round(len([1,2,3,4,5]) / 2) # why?
2
```
+
It seems as though Python rounded 2.5 to 2.
#### 💡 Explanation:
@@ -2615,13 +2851,13 @@ It seems as though Python rounded 2.5 to 2.
2.0
```
-- This is the recommended way to round .5 fractions as described in [IEEE 754](https://en.wikipedia.org/wiki/IEEE_754#Rounding_rules). However, the other way (round away from zero) is taught in school most of the time, so banker's rounding is likely not that well known. Furthermore, some of the most popular programming languages (for example: JavaScript, Java, C/C++, Ruby, Rust) do not use banker's rounding either. Therefore, this is still quite special to Python and may result in confusion when rounding fractions.
+- This is the recommended way to round .5 fractions as described in [IEEE 754](https://en.wikipedia.org/wiki/IEEE_754#Rounding_rules). However, the other way (round away from zero) is taught in school most of the time, so banker's rounding is likely not that well known. Furthermore, some of the most popular programming languages (for example: JavaScript, Java, C/C++, Ruby, Rust) do not use banker's rounding either. Therefore, this is still quite special to Python and may result in confusion when rounding fractions.
- See the [round() docs](https://docs.python.org/3/library/functions.html#round) or [this stackoverflow thread](https://stackoverflow.com/questions/10825926/python-3-x-rounding-behavior) for more information.
- Note that `get_middle([1])` only returned 1 because the index was `round(0.5) - 1 = 0 - 1 = -1`, returning the last element in the list.
---
-### ▶ Needles in a Haystack *
+### ▶ Needles in a Haystack \*
@@ -2715,7 +2951,7 @@ some_dict = {
"key_3": 3
}
-some_list = some_list.append(4)
+some_list = some_list.append(4)
some_dict = some_dict.update({"key_4": 4})
```
@@ -2757,20 +2993,20 @@ def similar_recursive_func(a):
#### 💡 Explanation:
-* For 1, the correct statement for expected behavior is `x, y = (0, 1) if True else (None, None)`.
+- For 1, the correct statement for expected behavior is `x, y = (0, 1) if True else (None, None)`.
-* For 2, the correct statement for expected behavior is `t = ('one',)` or `t = 'one',` (missing comma) otherwise the interpreter considers `t` to be a `str` and iterates over it character by character.
+- For 2, the correct statement for expected behavior is `t = ('one',)` or `t = 'one',` (missing comma) otherwise the interpreter considers `t` to be a `str` and iterates over it character by character.
-* `()` is a special token and denotes empty `tuple`.
+- `()` is a special token and denotes empty `tuple`.
-* In 3, as you might have already figured out, there's a missing comma after 5th element (`"that"`) in the list. So by implicit string literal concatenation,
+- In 3, as you might have already figured out, there's a missing comma after 5th element (`"that"`) in the list. So by implicit string literal concatenation,
```py
>>> ten_words_list
['some', 'very', 'big', 'list', 'thatconsists', 'of', 'exactly', 'ten', 'words']
```
-* No `AssertionError` was raised in 4th snippet because instead of asserting the individual expression `a == b`, we're asserting entire tuple. The following snippet will clear things up,
+- No `AssertionError` was raised in 4th snippet because instead of asserting the individual expression `a == b`, we're asserting entire tuple. The following snippet will clear things up,
```py
>>> a = "python"
@@ -2779,27 +3015,28 @@ def similar_recursive_func(a):
Traceback (most recent call last):
File "", line 1, in
AssertionError
-
+
>>> assert (a == b, "Values are not equal")
:1: SyntaxWarning: assertion is always true, perhaps remove parentheses?
-
+
>>> assert a == b, "Values are not equal"
Traceback (most recent call last):
File "", line 1, in
AssertionError: Values are not equal
```
-* As for the fifth snippet, most methods that modify the items of sequence/mapping objects like `list.append`, `dict.update`, `list.sort`, etc. modify the objects in-place and return `None`. The rationale behind this is to improve performance by avoiding making a copy of the object if the operation can be done in-place (Referred from [here](https://docs.python.org/3/faq/design.html#why-doesn-t-list-sort-return-the-sorted-list)).
+- As for the fifth snippet, most methods that modify the items of sequence/mapping objects like `list.append`, `dict.update`, `list.sort`, etc. modify the objects in-place and return `None`. The rationale behind this is to improve performance by avoiding making a copy of the object if the operation can be done in-place (Referred from [here](https://docs.python.org/3/faq/design.html#why-doesn-t-list-sort-return-the-sorted-list)).
-* Last one should be fairly obvious, mutable object (like `list`) can be altered in the function, and the reassignment of an immutable (`a -= 1`) is not an alteration of the value.
+- Last one should be fairly obvious, mutable object (like `list`) can be altered in the function, and the reassignment of an immutable (`a -= 1`) is not an alteration of the value.
-* Being aware of these nitpicks can save you hours of debugging effort in the long run.
+- Being aware of these nitpicks can save you hours of debugging effort in the long run.
---
+### ▶ Splitsies \*
-### ▶ Splitsies *
+
```py
>>> 'a'.split()
['a']
@@ -2820,21 +3057,23 @@ def similar_recursive_func(a):
#### 💡 Explanation:
- It might appear at first that the default separator for split is a single space `' '`, but as per the [docs](https://docs.python.org/3/library/stdtypes.html#str.split)
- > If sep is not specified or is `None`, a different splitting algorithm is applied: runs of consecutive whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the string has leading or trailing whitespace. Consequently, splitting an empty string or a string consisting of just whitespace with a None separator returns `[]`.
- > If sep is given, consecutive delimiters are not grouped together and are deemed to delimit empty strings (for example, `'1,,2'.split(',')` returns `['1', '', '2']`). Splitting an empty string with a specified separator returns `['']`.
+ > If sep is not specified or is `None`, a different splitting algorithm is applied: runs of consecutive whitespace are regarded as a single separator, and the result will contain no empty strings at the start or end if the string has leading or trailing whitespace. Consequently, splitting an empty string or a string consisting of just whitespace with a None separator returns `[]`.
+ > If sep is given, consecutive delimiters are not grouped together and are deemed to delimit empty strings (for example, `'1,,2'.split(',')` returns `['1', '', '2']`). Splitting an empty string with a specified separator returns `['']`.
- Noticing how the leading and trailing whitespaces are handled in the following snippet will make things clear,
- ```py
- >>> ' a '.split(' ')
- ['', 'a', '']
- >>> ' a '.split()
- ['a']
- >>> ''.split(' ')
- ['']
- ```
+
+ ```py
+ >>> ' a '.split(' ')
+ ['', 'a', '']
+ >>> ' a '.split()
+ ['a']
+ >>> ''.split(' ')
+ ['']
+ ```
---
-### ▶ Wild imports *
+### ▶ Wild imports \*
+
@@ -2865,35 +3104,39 @@ NameError: name '_another_weird_name_func' is not defined
- It is often advisable to not use wildcard imports. The first obvious reason for this is, in wildcard imports, the names with a leading underscore don't get imported. This may lead to errors during runtime.
- Had we used `from ... import a, b, c` syntax, the above `NameError` wouldn't have occurred.
- ```py
- >>> from module import some_weird_name_func_, _another_weird_name_func
- >>> _another_weird_name_func()
- works!
- ```
+
+ ```py
+ >>> from module import some_weird_name_func_, _another_weird_name_func
+ >>> _another_weird_name_func()
+ works!
+ ```
+
- If you really want to use wildcard imports, then you'd have to define the list `__all__` in your module that will contain a list of public objects that'll be available when we do wildcard imports.
- ```py
- __all__ = ['_another_weird_name_func']
- def some_weird_name_func_():
- print("works!")
+ ```py
+ __all__ = ['_another_weird_name_func']
- def _another_weird_name_func():
- print("works!")
- ```
- **Output**
+ def some_weird_name_func_():
+ print("works!")
- ```py
- >>> _another_weird_name_func()
- "works!"
- >>> some_weird_name_func_()
- Traceback (most recent call last):
- File "", line 1, in
- NameError: name 'some_weird_name_func_' is not defined
- ```
+ def _another_weird_name_func():
+ print("works!")
+ ```
+
+ **Output**
+
+ ```py
+ >>> _another_weird_name_func()
+ "works!"
+ >>> some_weird_name_func_()
+ Traceback (most recent call last):
+ File "", line 1, in
+ NameError: name 'some_weird_name_func_' is not defined
+ ```
---
-### ▶ All sorted? *
+### ▶ All sorted? \*
@@ -2911,7 +3154,7 @@ False
#### 💡 Explanation:
-- The `sorted` method always returns a list, and comparing lists and tuples always returns `False` in Python.
+- The `sorted` method always returns a list, and comparing lists and tuples always returns `False` in Python.
- ```py
>>> [] == tuple()
@@ -2935,7 +3178,9 @@ False
---
### ▶ Midnight time doesn't exist?
+
+
```py
from datetime import datetime
@@ -2957,6 +3202,7 @@ if noon_time:
```py
('Time at noon is', datetime.time(12, 0))
```
+
The midnight time is not printed.
#### 💡 Explanation:
@@ -2964,16 +3210,17 @@ The midnight time is not printed.
Before Python 3.5, the boolean value for `datetime.time` object was considered to be `False` if it represented midnight in UTC. It is error-prone when using the `if obj:` syntax to check if the `obj` is null or some equivalent of "empty."
---
----
-
+---
## Section: The Hidden treasures!
This section contains a few lesser-known and interesting things about Python that most beginners like me are unaware of (well, not anymore).
### ▶ Okay Python, Can you make me fly?
+
+
Well, here you go
```py
@@ -2984,13 +3231,15 @@ import antigravity
Sshh... It's a super-secret.
#### 💡 Explanation:
-+ `antigravity` module is one of the few easter eggs released by Python developers.
-+ `import antigravity` opens up a web browser pointing to the [classic XKCD comic](https://xkcd.com/353/) about Python.
-+ Well, there's more to it. There's **another easter egg inside the easter egg**. If you look at the [code](https://github.com/python/cpython/blob/master/Lib/antigravity.py#L7-L17), there's a function defined that purports to implement the [XKCD's geohashing algorithm](https://xkcd.com/426/).
+
+- `antigravity` module is one of the few easter eggs released by Python developers.
+- `import antigravity` opens up a web browser pointing to the [classic XKCD comic](https://xkcd.com/353/) about Python.
+- Well, there's more to it. There's **another easter egg inside the easter egg**. If you look at the [code](https://github.com/python/cpython/blob/master/Lib/antigravity.py#L7-L17), there's a function defined that purports to implement the [XKCD's geohashing algorithm](https://xkcd.com/426/).
---
### ▶ `goto`, but why?
+
```py
@@ -3006,6 +3255,7 @@ print("Freedom!")
```
**Output (Python 2.3):**
+
```py
I am trapped, please rescue!
I am trapped, please rescue!
@@ -3013,6 +3263,7 @@ Freedom!
```
#### 💡 Explanation:
+
- A working version of `goto` in Python was [announced](https://mail.python.org/pipermail/python-announce-list/2004-April/002982.html) as an April Fool's joke on 1st April 2004.
- Current versions of Python do not have this module.
- Although it works, but please don't use it. Here's the [reason](https://docs.python.org/3/faq/design.html#why-is-there-no-goto) to why `goto` is not present in Python.
@@ -3020,7 +3271,9 @@ Freedom!
---
### ▶ Brace yourself!
+
+
If you are one of the people who doesn't like using whitespace in Python to denote scopes, you can use the C-style {} by importing,
```py
@@ -3028,6 +3281,7 @@ from __future__ import braces
```
**Output:**
+
```py
File "some_file.py", line 1
from __future__ import braces
@@ -3037,16 +3291,20 @@ SyntaxError: not a chance
Braces? No way! If you think that's disappointing, use Java. Okay, another surprising thing, can you find where's the `SyntaxError` raised in `__future__` module [code](https://github.com/python/cpython/blob/master/Lib/__future__.py)?
#### 💡 Explanation:
-+ The `__future__` module is normally used to provide features from future versions of Python. The "future" in this specific context is however, ironic.
-+ This is an easter egg concerned with the community's feelings on this issue.
-+ The code is actually present [here](https://github.com/python/cpython/blob/025eb98dc0c1dc27404df6c544fc2944e0fa9f3a/Python/future.c#L49) in `future.c` file.
-+ When the CPython compiler encounters a [future statement](https://docs.python.org/3.3/reference/simple_stmts.html#future-statements), it first runs the appropriate code in `future.c` before treating it as a normal import statement.
+
+- The `__future__` module is normally used to provide features from future versions of Python. The "future" in this specific context is however, ironic.
+- This is an easter egg concerned with the community's feelings on this issue.
+- The code is actually present [here](https://github.com/python/cpython/blob/025eb98dc0c1dc27404df6c544fc2944e0fa9f3a/Python/future.c#L49) in `future.c` file.
+- When the CPython compiler encounters a [future statement](https://docs.python.org/3.3/reference/simple_stmts.html#future-statements), it first runs the appropriate code in `future.c` before treating it as a normal import statement.
---
### ▶ Let's meet Friendly Language Uncle For Life
+
+
**Output (Python 3.x)**
+
```py
>>> from __future__ import barry_as_FLUFL
>>> "Ruby" != "Python" # there's no doubt about it
@@ -3062,21 +3320,26 @@ True
There we go.
#### 💡 Explanation:
+
- This is relevant to [PEP-401](https://www.python.org/dev/peps/pep-0401/) released on April 1, 2009 (now you know, what it means).
- Quoting from the PEP-401
-
+
> Recognized that the != inequality operator in Python 3.0 was a horrible, finger-pain inducing mistake, the FLUFL reinstates the <> diamond operator as the sole spelling.
+
- There were more things that Uncle Barry had to share in the PEP; you can read them [here](https://www.python.org/dev/peps/pep-0401/).
- It works well in an interactive environment, but it will raise a `SyntaxError` when you run via python file (see this [issue](https://github.com/satwikkansal/wtfpython/issues/94)). However, you can wrap the statement inside an `eval` or `compile` to get it working,
- ```py
- from __future__ import barry_as_FLUFL
- print(eval('"Ruby" <> "Python"'))
- ```
+
+ ```py
+ from __future__ import barry_as_FLUFL
+ print(eval('"Ruby" <> "Python"'))
+ ```
---
### ▶ Even Python understands that love is complicated
+
+
```py
import this
```
@@ -3084,6 +3347,7 @@ import this
Wait, what's **this**? `this` is love :heart:
**Output:**
+
```
The Zen of Python, by Tim Peters
@@ -3126,14 +3390,16 @@ True
#### 💡 Explanation:
-* `this` module in Python is an easter egg for The Zen Of Python ([PEP 20](https://www.python.org/dev/peps/pep-0020)).
-* And if you think that's already interesting enough, check out the implementation of [this.py](https://hg.python.org/cpython/file/c3896275c0f6/Lib/this.py). Interestingly, **the code for the Zen violates itself** (and that's probably the only place where this happens).
-* Regarding the statement `love is not True or False; love is love`, ironic but it's self-explanatory (if not, please see the examples related to `is` and `is not` operators).
+- `this` module in Python is an easter egg for The Zen Of Python ([PEP 20](https://www.python.org/dev/peps/pep-0020)).
+- And if you think that's already interesting enough, check out the implementation of [this.py](https://hg.python.org/cpython/file/c3896275c0f6/Lib/this.py). Interestingly, **the code for the Zen violates itself** (and that's probably the only place where this happens).
+- Regarding the statement `love is not True or False; love is love`, ironic but it's self-explanatory (if not, please see the examples related to `is` and `is not` operators).
---
### ▶ Yes, it exists!
+
+
**The `else` clause for loops.** One typical example might be:
```py
@@ -3147,6 +3413,7 @@ True
```
**Output:**
+
```py
>>> some_list = [1, 2, 3, 4, 5]
>>> does_exists_num(some_list, 4)
@@ -3167,23 +3434,29 @@ else:
```
**Output:**
+
```py
Try block executed successfully...
```
#### 💡 Explanation:
+
- The `else` clause after a loop is executed only when there's no explicit `break` after all the iterations. You can think of it as a "nobreak" clause.
- `else` clause after a try block is also called "completion clause" as reaching the `else` clause in a `try` statement means that the try block actually completed successfully.
---
-### ▶ Ellipsis *
+
+### ▶ Ellipsis \*
+
+
```py
def some_func():
Ellipsis
```
**Output**
+
```py
>>> some_func()
# No output, No Error
@@ -3198,14 +3471,19 @@ Ellipsis
```
#### 💡 Explanation
+
- In Python, `Ellipsis` is a globally available built-in object which is equivalent to `...`.
- ```py
- >>> ...
- Ellipsis
- ```
+
+ ```py
+ >>> ...
+ Ellipsis
+ ```
+
- Ellipsis can be used for several purposes,
- + As a placeholder for code that hasn't been written yet (just like `pass` statement)
- + In slicing syntax to represent the full slices in remaining direction
+
+ - As a placeholder for code that hasn't been written yet (just like `pass` statement)
+ - In slicing syntax to represent the full slices in remaining direction
+
```py
>>> import numpy as np
>>> three_dimensional_array = np.arange(8).reshape(2, 2, 2)
@@ -3221,7 +3499,9 @@ Ellipsis
]
])
```
+
So our `three_dimensional_array` is an array of array of arrays. Let's say we want to print the second element (index `1`) of all the innermost arrays, we can use Ellipsis to bypass all the preceding dimensions
+
```py
>>> three_dimensional_array[:,:,1]
array([[1, 3],
@@ -3230,17 +3510,22 @@ Ellipsis
array([[1, 3],
[5, 7]])
```
+
Note: this will work for any number of dimensions. You can even select slice in first and last dimension and ignore the middle ones this way (`n_dimensional_array[firs_dim_slice, ..., last_dim_slice]`)
- + In [type hinting](https://docs.python.org/3/library/typing.html) to indicate only a part of the type (like `(Callable[..., int]` or `Tuple[str, ...]`))
- + You may also use Ellipsis as a default function argument (in the cases when you want to differentiate between the "no argument passed" and "None value passed" scenarios).
+
+ - In [type hinting](https://docs.python.org/3/library/typing.html) to indicate only a part of the type (like `(Callable[..., int]` or `Tuple[str, ...]`))
+ - You may also use Ellipsis as a default function argument (in the cases when you want to differentiate between the "no argument passed" and "None value passed" scenarios).
---
### ▶ Inpinity
+
+
The spelling is intended. Please, don't submit a patch for this.
**Output (Python 3.x):**
+
```py
>>> infinity = float('infinity')
>>> hash(infinity)
@@ -3250,14 +3535,18 @@ The spelling is intended. Please, don't submit a patch for this.
```
#### 💡 Explanation:
+
- Hash of infinity is 10⁵ x π.
- Interestingly, the hash of `float('-inf')` is "-10⁵ x π" in Python 3, whereas "-10⁵ x e" in Python 2.
---
### ▶ Let's mangle
+
+
1\.
+
```py
class Yo(object):
def __init__(self):
@@ -3266,6 +3555,7 @@ class Yo(object):
```
**Output:**
+
```py
>>> Yo().bro
True
@@ -3276,6 +3566,7 @@ True
```
2\.
+
```py
class Yo(object):
def __init__(self):
@@ -3285,6 +3576,7 @@ class Yo(object):
```
**Output:**
+
```py
>>> Yo().bro
True
@@ -3308,6 +3600,7 @@ class A(object):
```
**Output:**
+
```py
>>> A().__variable
Traceback (most recent call last):
@@ -3318,24 +3611,27 @@ AttributeError: 'A' object has no attribute '__variable'
'Some value'
```
-
#### 💡 Explanation:
-* [Name Mangling](https://en.wikipedia.org/wiki/Name_mangling) is used to avoid naming collisions between different namespaces.
-* In Python, the interpreter modifies (mangles) the class member names starting with `__` (double underscore a.k.a "dunder") and not ending with more than one trailing underscore by adding `_NameOfTheClass` in front.
-* So, to access `__honey` attribute in the first snippet, we had to append `_Yo` to the front, which would prevent conflicts with the same name attribute defined in any other class.
-* But then why didn't it work in the second snippet? Because name mangling excludes the names ending with double underscores.
-* The third snippet was also a consequence of name mangling. The name `__variable` in the statement `return __variable` was mangled to `_A__variable`, which also happens to be the name of the variable we declared in the outer scope.
-* Also, if the mangled name is longer than 255 characters, truncation will happen.
+- [Name Mangling](https://en.wikipedia.org/wiki/Name_mangling) is used to avoid naming collisions between different namespaces.
+- In Python, the interpreter modifies (mangles) the class member names starting with `__` (double underscore a.k.a "dunder") and not ending with more than one trailing underscore by adding `_NameOfTheClass` in front.
+- So, to access `__honey` attribute in the first snippet, we had to append `_Yo` to the front, which would prevent conflicts with the same name attribute defined in any other class.
+- But then why didn't it work in the second snippet? Because name mangling excludes the names ending with double underscores.
+- The third snippet was also a consequence of name mangling. The name `__variable` in the statement `return __variable` was mangled to `_A__variable`, which also happens to be the name of the variable we declared in the outer scope.
+- Also, if the mangled name is longer than 255 characters, truncation will happen.
---
+
---
## Section: Appearances are deceptive!
### ▶ Skipping lines?
+
+
**Output:**
+
```py
>>> value = 11
>>> valuе = 32
@@ -3387,6 +3683,7 @@ def energy_receive():
```
**Output:**
+
```py
>>> energy_send(123.456)
>>> energy_receive()
@@ -3397,13 +3694,15 @@ Where's the Nobel Prize?
#### 💡 Explanation:
-* Notice that the numpy array created in the `energy_send` function is not returned, so that memory space is free to reallocate.
-* `numpy.empty()` returns the next free memory slot without reinitializing it. This memory spot just happens to be the same one that was just freed (usually, but not always).
+- Notice that the numpy array created in the `energy_send` function is not returned, so that memory space is free to reallocate.
+- `numpy.empty()` returns the next free memory slot without reinitializing it. This memory spot just happens to be the same one that was just freed (usually, but not always).
---
### ▶ Well, something is fishy...
+
+
```py
def square(x):
"""
@@ -3428,25 +3727,28 @@ Shouldn't that be 100?
#### 💡 Explanation
-* **Don't mix tabs and spaces!** The character just preceding return is a "tab", and the code is indented by multiple of "4 spaces" elsewhere in the example.
-* This is how Python handles tabs:
-
+- **Don't mix tabs and spaces!** The character just preceding return is a "tab", and the code is indented by multiple of "4 spaces" elsewhere in the example.
+- This is how Python handles tabs:
+
> First, tabs are replaced (from left to right) by one to eight spaces such that the total number of characters up to and including the replacement is a multiple of eight <...>
-* So the "tab" at the last line of `square` function is replaced with eight spaces, and it gets into the loop.
-* Python 3 is kind enough to throw an error for such cases automatically.
- **Output (Python 3.x):**
- ```py
- TabError: inconsistent use of tabs and spaces in indentation
- ```
+- So the "tab" at the last line of `square` function is replaced with eight spaces, and it gets into the loop.
+- Python 3 is kind enough to throw an error for such cases automatically.
+
+ **Output (Python 3.x):**
+
+ ```py
+ TabError: inconsistent use of tabs and spaces in indentation
+ ```
---
+
---
## Section: Miscellaneous
-
### ▶ `+=` is faster
+
```py
@@ -3459,12 +3761,15 @@ Shouldn't that be 100?
```
#### 💡 Explanation:
-+ `+=` is faster than `+` for concatenating more than two strings because the first string (example, `s1` for `s1 += s2 + s3`) is not destroyed while calculating the complete string.
+
+- `+=` is faster than `+` for concatenating more than two strings because the first string (example, `s1` for `s1 += s2 + s3`) is not destroyed while calculating the complete string.
---
### ▶ Let's make a giant string!
+
+
```py
def add_string_with_plus(iters):
s = ""
@@ -3534,11 +3839,13 @@ Let's increase the number of iterations by a factor of 10.
```
#### 💡 Explanation
+
- You can read more about [timeit](https://docs.python.org/3/library/timeit.html) or [%timeit](https://ipython.org/ipython-doc/dev/interactive/magics.html#magic-timeit) on these links. They are used to measure the execution time of code pieces.
- Don't use `+` for generating long strings — In Python, `str` is immutable, so the left and right strings have to be copied into the new string for every pair of concatenations. If you concatenate four strings of length 10, you'll be copying (10+10) + ((10+10)+10) + (((10+10)+10)+10) = 90 characters instead of just 40 characters. Things get quadratically worse as the number and size of the string increases (justified with the execution times of `add_bytes_with_plus` function)
- Therefore, it's advised to use `.format.` or `%` syntax (however, they are slightly slower than `+` for very short strings).
- Or better, if already you've contents available in the form of an iterable object, then use `''.join(iterable_object)` which is much faster.
- Unlike `add_bytes_with_plus` because of the `+=` optimizations discussed in the previous example, `add_string_with_plus` didn't show a quadratic increase in execution time. Had the statement been `s = s + "x" + "y" + "z"` instead of `s += "xyz"`, the increase would have been quadratic.
+
```py
def add_string_with_plus(iters):
s = ""
@@ -3551,20 +3858,24 @@ Let's increase the number of iterations by a factor of 10.
>>> %timeit -n100 add_string_with_plus(10000) # Quadratic increase in execution time
9 ms ± 298 µs per loop (mean ± std. dev. of 7 runs, 100 loops each)
```
+
- So many ways to format and create a giant string are somewhat in contrast to the [Zen of Python](https://www.python.org/dev/peps/pep-0020/), according to which,
-
- > There should be one-- and preferably only one --obvious way to do it.
+
+ > There should be one-- and preferably only one --obvious way to do it.
---
-### ▶ Slowing down `dict` lookups *
+### ▶ Slowing down `dict` lookups \*
+
+
```py
some_dict = {str(i): 1 for i in range(1_000_000)}
another_dict = {str(i): 1 for i in range(1_000_000)}
```
**Output:**
+
```py
>>> %timeit some_dict['5']
28.6 ns ± 0.115 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)
@@ -3581,17 +3892,20 @@ KeyError: 1
>>> %timeit another_dict['5']
38.5 ns ± 0.0913 ns per loop (mean ± std. dev. of 7 runs, 10000000 loops each)
```
+
Why are same lookups becoming slower?
#### 💡 Explanation:
-+ CPython has a generic dictionary lookup function that handles all types of keys (`str`, `int`, any object ...), and a specialized one for the common case of dictionaries composed of `str`-only keys.
-+ The specialized function (named `lookdict_unicode` in CPython's [source](https://github.com/python/cpython/blob/522691c46e2ae51faaad5bbbce7d959dd61770df/Objects/dictobject.c#L841)) knows all existing keys (including the looked-up key) are strings, and uses the faster & simpler string comparison to compare keys, instead of calling the `__eq__` method.
-+ The first time a `dict` instance is accessed with a non-`str` key, it's modified so future lookups use the generic function.
-+ This process is not reversible for the particular `dict` instance, and the key doesn't even have to exist in the dictionary. That's why attempting a failed lookup has the same effect.
+- CPython has a generic dictionary lookup function that handles all types of keys (`str`, `int`, any object ...), and a specialized one for the common case of dictionaries composed of `str`-only keys.
+- The specialized function (named `lookdict_unicode` in CPython's [source](https://github.com/python/cpython/blob/522691c46e2ae51faaad5bbbce7d959dd61770df/Objects/dictobject.c#L841)) knows all existing keys (including the looked-up key) are strings, and uses the faster & simpler string comparison to compare keys, instead of calling the `__eq__` method.
+- The first time a `dict` instance is accessed with a non-`str` key, it's modified so future lookups use the generic function.
+- This process is not reversible for the particular `dict` instance, and the key doesn't even have to exist in the dictionary. That's why attempting a failed lookup has the same effect.
+
+### ▶ Bloating instance `dict`s \*
-### ▶ Bloating instance `dict`s *
+
```py
import sys
@@ -3609,6 +3923,7 @@ def dict_size(o):
```
**Output:** (Python 3.8, other Python 3 versions may vary a little)
+
```py
>>> o1 = SomeClass()
>>> o2 = SomeClass()
@@ -3645,25 +3960,29 @@ Let's try again... In a new interpreter:
What makes those dictionaries become bloated? And why are newly created objects bloated as well?
#### 💡 Explanation:
-+ CPython is able to reuse the same "keys" object in multiple dictionaries. This was added in [PEP 412](https://www.python.org/dev/peps/pep-0412/) with the motivation to reduce memory usage, specifically in dictionaries of instances - where keys (instance attributes) tend to be common to all instances.
-+ This optimization is entirely seamless for instance dictionaries, but it is disabled if certain assumptions are broken.
-+ Key-sharing dictionaries do not support deletion; if an instance attribute is deleted, the dictionary is "unshared", and key-sharing is disabled for all future instances of the same class.
-+ Additionally, if the dictionary keys have been resized (because new keys are inserted), they are kept shared *only* if they are used by a exactly single dictionary (this allows adding many attributes in the `__init__` of the very first created instance, without causing an "unshare"). If multiple instances exist when a resize happens, key-sharing is disabled for all future instances of the same class: CPython can't tell if your instances are using the same set of attributes anymore, and decides to bail out on attempting to share their keys.
-+ A small tip, if you aim to lower your program's memory footprint: don't delete instance attributes, and make sure to initialize all attributes in your `__init__`!
+- CPython is able to reuse the same "keys" object in multiple dictionaries. This was added in [PEP 412](https://www.python.org/dev/peps/pep-0412/) with the motivation to reduce memory usage, specifically in dictionaries of instances - where keys (instance attributes) tend to be common to all instances.
+- This optimization is entirely seamless for instance dictionaries, but it is disabled if certain assumptions are broken.
+- Key-sharing dictionaries do not support deletion; if an instance attribute is deleted, the dictionary is "unshared", and key-sharing is disabled for all future instances of the same class.
+- Additionally, if the dictionary keys have been resized (because new keys are inserted), they are kept shared _only_ if they are used by a exactly single dictionary (this allows adding many attributes in the `__init__` of the very first created instance, without causing an "unshare"). If multiple instances exist when a resize happens, key-sharing is disabled for all future instances of the same class: CPython can't tell if your instances are using the same set of attributes anymore, and decides to bail out on attempting to share their keys.
+- A small tip, if you aim to lower your program's memory footprint: don't delete instance attributes, and make sure to initialize all attributes in your `__init__`!
+
+### ▶ Minor Ones \*
-### ▶ Minor Ones *
-* `join()` is a string operation instead of list operation. (sort of counter-intuitive at first usage)
+
+- `join()` is a string operation instead of list operation. (sort of counter-intuitive at first usage)
**💡 Explanation:** If `join()` is a method on a string, then it can operate on any iterable (list, tuple, iterators). If it were a method on a list, it'd have to be implemented separately by every type. Also, it doesn't make much sense to put a string-specific method on a generic `list` object API.
-
-* Few weird looking but semantically correct statements:
- + `[] = ()` is a semantically correct statement (unpacking an empty `tuple` into an empty `list`)
- + `'a'[0][0][0][0][0]` is also semantically correct, because Python doesn't have a character data type like other languages branched from C. So selecting a single character from a string returns a single-character string.
- + `3 --0-- 5 == 8` and `--5 == 5` are both semantically correct statements and evaluate to `True`.
-* Given that `a` is a number, `++a` and `--a` are both valid Python statements but don't behave the same way as compared with similar statements in languages like C, C++, or Java.
+- Few weird looking but semantically correct statements:
+
+ - `[] = ()` is a semantically correct statement (unpacking an empty `tuple` into an empty `list`)
+ - `'a'[0][0][0][0][0]` is also semantically correct, because Python doesn't have a character data type like other languages branched from C. So selecting a single character from a string returns a single-character string.
+ - `3 --0-- 5 == 8` and `--5 == 5` are both semantically correct statements and evaluate to `True`.
+
+- Given that `a` is a number, `++a` and `--a` are both valid Python statements but don't behave the same way as compared with similar statements in languages like C, C++, or Java.
+
```py
>>> a = 5
>>> a
@@ -3675,116 +3994,125 @@ What makes those dictionaries become bloated? And why are newly created objects
```
**💡 Explanation:**
- + There is no `++` operator in Python grammar. It is actually two `+` operators.
- + `++a` parses as `+(+a)` which translates to `a`. Similarly, the output of the statement `--a` can be justified.
- + This StackOverflow [thread](https://stackoverflow.com/questions/3654830/why-are-there-no-and-operators-in-python) discusses the rationale behind the absence of increment and decrement operators in Python.
-* You must be aware of the Walrus operator in Python. But have you ever heard about *the space-invader operator*?
+ - There is no `++` operator in Python grammar. It is actually two `+` operators.
+ - `++a` parses as `+(+a)` which translates to `a`. Similarly, the output of the statement `--a` can be justified.
+ - This StackOverflow [thread](https://stackoverflow.com/questions/3654830/why-are-there-no-and-operators-in-python) discusses the rationale behind the absence of increment and decrement operators in Python.
+
+- You must be aware of the Walrus operator in Python. But have you ever heard about _the space-invader operator_?
+
```py
>>> a = 42
>>> a -=- 1
>>> a
43
```
+
It is used as an alternative incrementation operator, together with another one
+
```py
>>> a +=+ 1
>>> a
>>> 44
```
+
**💡 Explanation:** This prank comes from [Raymond Hettinger's tweet](https://twitter.com/raymondh/status/1131103570856632321?lang=en). The space invader operator is actually just a malformatted `a -= (-1)`. Which is equivalent to `a = a - (- 1)`. Similar for the `a += (+ 1)` case.
-
-* Python has an undocumented [converse implication](https://en.wikipedia.org/wiki/Converse_implication) operator.
-
- ```py
- >>> False ** False == True
- True
- >>> False ** True == False
- True
- >>> True ** False == True
- True
- >>> True ** True == True
- True
- ```
-
- **💡 Explanation:** If you replace `False` and `True` by 0 and 1 and do the maths, the truth table is equivalent to a converse implication operator. ([Source](https://github.com/cosmologicon/pywat/blob/master/explanation.md#the-undocumented-converse-implication-operator))
-
-* Since we are talking operators, there's also `@` operator for matrix multiplication (don't worry, this time it's for real).
-
- ```py
- >>> import numpy as np
- >>> np.array([2, 2, 2]) @ np.array([7, 8, 8])
- 46
- ```
-
- **💡 Explanation:** The `@` operator was added in Python 3.5 keeping the scientific community in mind. Any object can overload `__matmul__` magic method to define behavior for this operator.
-
-* From Python 3.8 onwards you can use a typical f-string syntax like `f'{some_var=}` for quick debugging. Example,
- ```py
- >>> some_string = "wtfpython"
- >>> f'{some_string=}'
- "some_string='wtfpython'"
- ```
-
-* Python uses 2 bytes for local variable storage in functions. In theory, this means that only 65536 variables can be defined in a function. However, python has a handy solution built in that can be used to store more than 2^16 variable names. The following code demonstrates what happens in the stack when more than 65536 local variables are defined (Warning: This code prints around 2^18 lines of text, so be prepared!):
-
- ```py
- import dis
- exec("""
- def f():
- """ + """
- """.join(["X" + str(x) + "=" + str(x) for x in range(65539)]))
-
- f()
-
- print(dis.dis(f))
- ```
-
-* Multiple Python threads won't run your *Python code* concurrently (yes, you heard it right!). It may seem intuitive to spawn several threads and let them execute your Python code concurrently, but, because of the [Global Interpreter Lock](https://wiki.python.org/moin/GlobalInterpreterLock) in Python, all you're doing is making your threads execute on the same core turn by turn. Python threads are good for IO-bound tasks, but to achieve actual parallelization in Python for CPU-bound tasks, you might want to use the Python [multiprocessing](https://docs.python.org/3/library/multiprocessing.html) module.
-* Sometimes, the `print` method might not print values immediately. For example,
+- Python has an undocumented [converse implication](https://en.wikipedia.org/wiki/Converse_implication) operator.
+
+ ```py
+ >>> False ** False == True
+ True
+ >>> False ** True == False
+ True
+ >>> True ** False == True
+ True
+ >>> True ** True == True
+ True
+ ```
+
+ **💡 Explanation:** If you replace `False` and `True` by 0 and 1 and do the maths, the truth table is equivalent to a converse implication operator. ([Source](https://github.com/cosmologicon/pywat/blob/master/explanation.md#the-undocumented-converse-implication-operator))
+
+- Since we are talking operators, there's also `@` operator for matrix multiplication (don't worry, this time it's for real).
- ```py
- # File some_file.py
- import time
-
- print("wtfpython", end="_")
- time.sleep(3)
- ```
+ ```py
+ >>> import numpy as np
+ >>> np.array([2, 2, 2]) @ np.array([7, 8, 8])
+ 46
+ ```
- This will print the `wtfpython` after 3 seconds due to the `end` argument because the output buffer is flushed either after encountering `\n` or when the program finishes execution. We can force the buffer to flush by passing `flush=True` argument.
+ **💡 Explanation:** The `@` operator was added in Python 3.5 keeping the scientific community in mind. Any object can overload `__matmul__` magic method to define behavior for this operator.
+
+- From Python 3.8 onwards you can use a typical f-string syntax like `f'{some_var=}` for quick debugging. Example,
+
+ ```py
+ >>> some_string = "wtfpython"
+ >>> f'{some_string=}'
+ "some_string='wtfpython'"
+ ```
+
+- Python uses 2 bytes for local variable storage in functions. In theory, this means that only 65536 variables can be defined in a function. However, python has a handy solution built in that can be used to store more than 2^16 variable names. The following code demonstrates what happens in the stack when more than 65536 local variables are defined (Warning: This code prints around 2^18 lines of text, so be prepared!):
+
+ ```py
+ import dis
+ exec("""
+ def f():
+ """ + """
+ """.join(["X" + str(x) + "=" + str(x) for x in range(65539)]))
+
+ f()
+
+ print(dis.dis(f))
+ ```
+
+- Multiple Python threads won't run your _Python code_ concurrently (yes, you heard it right!). It may seem intuitive to spawn several threads and let them execute your Python code concurrently, but, because of the [Global Interpreter Lock](https://wiki.python.org/moin/GlobalInterpreterLock) in Python, all you're doing is making your threads execute on the same core turn by turn. Python threads are good for IO-bound tasks, but to achieve actual parallelization in Python for CPU-bound tasks, you might want to use the Python [multiprocessing](https://docs.python.org/3/library/multiprocessing.html) module.
+
+- Sometimes, the `print` method might not print values immediately. For example,
+
+ ```py
+ # File some_file.py
+ import time
+
+ print("wtfpython", end="_")
+ time.sleep(3)
+ ```
+
+ This will print the `wtfpython` after 3 seconds due to the `end` argument because the output buffer is flushed either after encountering `\n` or when the program finishes execution. We can force the buffer to flush by passing `flush=True` argument.
+
+- List slicing with out of the bounds indices throws no errors
-* List slicing with out of the bounds indices throws no errors
```py
>>> some_list = [1, 2, 3, 4, 5]
>>> some_list[111:]
[]
```
-* Slicing an iterable not always creates a new object. For example,
- ```py
- >>> some_str = "wtfpython"
- >>> some_list = ['w', 't', 'f', 'p', 'y', 't', 'h', 'o', 'n']
- >>> some_list is some_list[:] # False expected because a new object is created.
- False
- >>> some_str is some_str[:] # True because strings are immutable, so making a new object is of not much use.
- True
- ```
+- Slicing an iterable not always creates a new object. For example,
-* `int('١٢٣٤٥٦٧٨٩')` returns `123456789` in Python 3. In Python, Decimal characters include digit characters, and all characters that can be used to form decimal-radix numbers, e.g. U+0660, ARABIC-INDIC DIGIT ZERO. Here's an [interesting story](https://chris.improbable.org/2014/8/25/adventures-in-unicode-digits/) related to this behavior of Python.
+ ```py
+ >>> some_str = "wtfpython"
+ >>> some_list = ['w', 't', 'f', 'p', 'y', 't', 'h', 'o', 'n']
+ >>> some_list is some_list[:] # False expected because a new object is created.
+ False
+ >>> some_str is some_str[:] # True because strings are immutable, so making a new object is of not much use.
+ True
+ ```
-* You can separate numeric literals with underscores (for better readability) from Python 3 onwards.
+- `int('١٢٣٤٥٦٧٨٩')` returns `123456789` in Python 3. In Python, Decimal characters include digit characters, and all characters that can be used to form decimal-radix numbers, e.g. U+0660, ARABIC-INDIC DIGIT ZERO. Here's an [interesting story](https://chris.improbable.org/2014/8/25/adventures-in-unicode-digits/) related to this behavior of Python.
- ```py
- >>> six_million = 6_000_000
- >>> six_million
- 6000000
- >>> hex_address = 0xF00D_CAFE
- >>> hex_address
- 4027435774
- ```
+- You can separate numeric literals with underscores (for better readability) from Python 3 onwards.
+
+ ```py
+ >>> six_million = 6_000_000
+ >>> six_million
+ 6000000
+ >>> hex_address = 0xF00D_CAFE
+ >>> hex_address
+ 4027435774
+ ```
+
+- `'abc'.count('') == 4`. Here's an approximate implementation of `count` method, which would make the things more clear
-* `'abc'.count('') == 4`. Here's an approximate implementation of `count` method, which would make the things more clear
```py
def count(s, sub):
result = 0
@@ -3792,9 +4120,11 @@ What makes those dictionaries become bloated? And why are newly created objects
result += (s[i:i + len(sub)] == sub)
return result
```
+
The behavior is due to the matching of empty substring(`''`) with slices of length 0 in the original string.
---
+
---
# Contributing
@@ -3816,15 +4146,16 @@ PS: Please don't reach out with backlinking requests, no links will be added unl
The idea and design for this collection were initially inspired by Denys Dovhan's awesome project [wtfjs](https://github.com/denysdovhan/wtfjs). The overwhelming support by Pythonistas gave it the shape it is in right now.
#### Some nice Links!
-* https://www.youtube.com/watch?v=sH4XF6pKKmk
-* https://www.reddit.com/r/Python/comments/3cu6ej/what_are_some_wtf_things_about_python
-* https://sopython.com/wiki/Common_Gotchas_In_Python
-* https://stackoverflow.com/questions/530530/python-2-x-gotchas-and-landmines
-* https://stackoverflow.com/questions/1011431/common-pitfalls-in-python
-* https://www.python.org/doc/humor/
-* https://github.com/cosmologicon/pywat#the-undocumented-converse-implication-operator
-* https://github.com/wemake-services/wemake-python-styleguide/search?q=wtfpython&type=Issues
-* WFTPython discussion threads on [Hacker News](https://news.ycombinator.com/item?id=21862073) and [Reddit](https://www.reddit.com/r/programming/comments/edsh3q/what_the_fck_python_30_exploring_and/).
+
+- https://www.youtube.com/watch?v=sH4XF6pKKmk
+- https://www.reddit.com/r/Python/comments/3cu6ej/what_are_some_wtf_things_about_python
+- https://sopython.com/wiki/Common_Gotchas_In_Python
+- https://stackoverflow.com/questions/530530/python-2-x-gotchas-and-landmines
+- https://stackoverflow.com/questions/1011431/common-pitfalls-in-python
+- https://www.python.org/doc/humor/
+- https://github.com/cosmologicon/pywat#the-undocumented-converse-implication-operator
+- https://github.com/wemake-services/wemake-python-styleguide/search?q=wtfpython&type=Issues
+- WFTPython discussion threads on [Hacker News](https://news.ycombinator.com/item?id=21862073) and [Reddit](https://www.reddit.com/r/programming/comments/edsh3q/what_the_fck_python_30_exploring_and/).
# 🎓 License
@@ -3839,11 +4170,10 @@ The idea and design for this collection were initially inspired by Denys Dovhan'
If you like wtfpython, you can use these quick links to share it with your friends,
-[Twitter](https://twitter.com/intent/tweet?url=https://github.com/satwikkansal/wtfpython&text=If%20you%20really%20think%20you%20know%20Python,%20think%20once%20more!%20Check%20out%20wtfpython&hashtags=python,wtfpython) | [Linkedin](https://www.linkedin.com/shareArticle?url=https://github.com/satwikkansal&title=What%20the%20f*ck%20Python!&summary=If%20you%20really%20thing%20you%20know%20Python,%20think%20once%20more!) | [Facebook](https://www.facebook.com/dialog/share?app_id=536779657179021&display=page&href=https%3A%2F%2Fgithub.com%2Fsatwikkansal%2Fwtfpython"e=If%20you%20really%20think%20you%20know%20Python%2C%20think%20once%20more!)
+[Twitter](https://twitter.com/intent/tweet?url=https://github.com/satwikkansal/wtfpython&text=If%20you%20really%20think%20you%20know%20Python,%20think%20once%20more!%20Check%20out%20wtfpython&hashtags=python,wtfpython) | [Linkedin](https://www.linkedin.com/shareArticle?url=https://github.com/satwikkansal&title=What%20the%20f*ck%20Python!&summary=If%20you%20really%20thing%20you%20know%20Python,%20think%20once%20more!) | [Facebook](https://www.facebook.com/dialog/share?app_id=536779657179021&display=page&href=https%3A%2F%2Fgithub.com%2Fsatwikkansal%2Fwtfpython"e=If%20you%20really%20think%20you%20know%20Python%2C%20think%20once%20more!)
## Need a pdf version?
I've received a few requests for the pdf (and epub) version of wtfpython. You can add your details [here](https://form.jotform.com/221593245656057) to get them as soon as they are finished.
-
**That's all folks!** For upcoming content like this, you can add your email [here](https://form.jotform.com/221593598380062).
diff --git a/images/expanding-brain-meme.jpg b/images/expanding-brain-meme.jpg
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--- /dev/null
+++ b/images/logo.svg
@@ -0,0 +1,38 @@
+
+
+
diff --git a/images/logo_dark_theme.svg b/images/logo_dark_theme.svg
new file mode 100755
index 00000000..f89e7970
--- /dev/null
+++ b/images/logo_dark_theme.svg
@@ -0,0 +1,38 @@
+
+
+
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index 00000000..0572a9e3
--- /dev/null
+++ b/images/string-intern/string_interning.svg
@@ -0,0 +1,4 @@
+
+
+
+
diff --git a/images/string-intern/string_interning_dark_theme.svg b/images/string-intern/string_interning_dark_theme.svg
new file mode 100755
index 00000000..69c32e40
--- /dev/null
+++ b/images/string-intern/string_interning_dark_theme.svg
@@ -0,0 +1,4 @@
+
+
+
+
diff --git a/images/tic-tac-toe.png b/images/tic-tac-toe.png
deleted file mode 100644
index 9c25117b..00000000
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new file mode 100755
index 00000000..02b1dad0
--- /dev/null
+++ b/images/tic-tac-toe/after_board_initialized.svg
@@ -0,0 +1,4 @@
+
+
+
+
\ No newline at end of file
diff --git a/images/tic-tac-toe/after_board_initialized_dark_theme.svg b/images/tic-tac-toe/after_board_initialized_dark_theme.svg
new file mode 100755
index 00000000..3218ad06
--- /dev/null
+++ b/images/tic-tac-toe/after_board_initialized_dark_theme.svg
@@ -0,0 +1,4 @@
+
+
+
+
\ No newline at end of file
diff --git a/images/tic-tac-toe/after_row_initialized.png b/images/tic-tac-toe/after_row_initialized.png
deleted file mode 100644
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new file mode 100755
index 00000000..92eb02cd
--- /dev/null
+++ b/images/tic-tac-toe/after_row_initialized.svg
@@ -0,0 +1,4 @@
+
+
+
+
\ No newline at end of file
diff --git a/images/tic-tac-toe/after_row_initialized_dark_theme.svg b/images/tic-tac-toe/after_row_initialized_dark_theme.svg
new file mode 100755
index 00000000..24049580
--- /dev/null
+++ b/images/tic-tac-toe/after_row_initialized_dark_theme.svg
@@ -0,0 +1,4 @@
+
+
+
+
\ No newline at end of file
diff --git a/irrelevant/wtf.ipynb b/irrelevant/wtf.ipynb
index a3147e19..c0f3d669 100644
--- a/irrelevant/wtf.ipynb
+++ b/irrelevant/wtf.ipynb
@@ -4,13 +4,13 @@
"cell_type": "markdown",
"metadata": {},
"source": [
- "
\n",
+ "\n",
"
What the f*ck Python! \ud83d\ude31
\n",
"
Exploring and understanding Python through surprising snippets.
\n",
"\n",
"Translations: [Chinese \u4e2d\u6587](https://github.com/leisurelicht/wtfpython-cn) | [Vietnamese Ti\u1ebfng Vi\u1ec7t](https://github.com/vuduclyunitn/wtfptyhon-vi) | [Add translation](https://github.com/satwikkansal/wtfpython/issues/new?title=Add%20translation%20for%20[LANGUAGE]&body=Expected%20time%20to%20finish:%20[X]%20weeks.%20I%27ll%20start%20working%20on%20it%20from%20[Y].)\n",
"\n",
- "Other modes: [Interactive](https://colab.research.google.com/github/satwikkansal/wtfpython/blob/master/irrelevant/wtf.ipynb) | [CLI](https://pypi.python.org/pypi/wtfpython)\n",
+ "Other modes: [Interactive](https://colab.research.google.com/github/satwikkansal/wtfpython/blob/master/irrelevant/wtf.ipynb)\n",
"\n",
"Python, being a beautifully designed high-level and interpreter-based programming language, provides us with many features for the programmer's comfort. But sometimes, the outcomes of a Python snippet may not seem obvious at first sight.\n",
"\n",
@@ -71,15 +71,6 @@
" - If the answer is no (which is perfectly okay), take a deep breath, and read the explanation (and if you still don't understand, shout out! and create an issue [here](https://github.com/satwikkansal/wtfpython/issues/new)).\n",
" - If yes, give a gentle pat on your back, and you may skip to the next example.\n",
"\n",
- "PS: You can also read WTFPython at the command line using the [pypi package](https://pypi.python.org/pypi/wtfpython),\n",
- "```sh\n",
- "$ pip install wtfpython -U\n",
- "$ wtfpython\n",
- "```\n",
- "---\n",
- "\n",
- "# \ud83d\udc40 Examples\n",
- "\n",
"\n\n## Hosted notebook instructions\n\nThis is just an experimental attempt of browsing wtfpython through jupyter notebooks. Some examples are read-only because, \n- they either require a version of Python that's not supported in the hosted runtime.\n- or they can't be reproduced in the notebook envrinonment.\n\nThe expected outputs are already present in collapsed cells following the code cells. The Google colab provides Python2 (2.7) and Python3 (3.6, default) runtimes. You can switch among these for Python2 specific examples. For examples specific to other minor versions, you can simply refer to collapsed outputs (it's not possible to control the minor version in hosted notebooks as of now). You can check the active version using\n\n```py\n>>> import sys\n>>> sys.version\n# Prints out Python version here.\n```\n\nThat being said, most of the examples do work as expected. If you face any trouble, feel free to consult the original content on wtfpython and create an issue in the repo. Have fun!\n\n---\n"
]
},
@@ -355,7 +346,7 @@
" * All length 0 and length 1 strings are interned.\n",
" * Strings are interned at compile time (`'wtf'` will be interned but `''.join(['w', 't', 'f'])` will not be interned)\n",
" * Strings that are not composed of ASCII letters, digits or underscores, are not interned. This explains why `'wtf!'` was not interned due to `!`. CPython implementation of this rule can be found [here](https://github.com/python/cpython/blob/3.6/Objects/codeobject.c#L19)\n",
- " \n",
+ "\n",
"+ When `a` and `b` are set to `\"wtf!\"` in the same line, the Python interpreter creates a new object, then references the second variable at the same time. If you do it on separate lines, it doesn't \"know\" that there's already `\"wtf!\"` as an object (because `\"wtf!\"` is not implicitly interned as per the facts mentioned above). It's a compile-time optimization. This optimization doesn't apply to 3.7.x versions of CPython (check this [issue](https://github.com/satwikkansal/wtfpython/issues/100) for more discussion).\n",
"+ A compile unit in an interactive environment like IPython consists of a single statement, whereas it consists of the entire module in case of modules. `a, b = \"wtf!\", \"wtf!\"` is single statement, whereas `a = \"wtf!\"; b = \"wtf!\"` are two statements in a single line. This explains why the identities are different in `a = \"wtf!\"; b = \"wtf!\"`, and also explain why they are same when invoked in `some_file.py`\n",
"+ The abrupt change in the output of the fourth snippet is due to a [peephole optimization](https://en.wikipedia.org/wiki/Peephole_optimization) technique known as Constant folding. This means the expression `'a'*20` is replaced by `'aaaaaaaaaaaaaaaaaaaa'` during compilation to save a few clock cycles during runtime. Constant folding only occurs for strings having a length of less than 21. (Why? Imagine the size of `.pyc` file generated as a result of the expression `'a'*10**10`). [Here's](https://github.com/python/cpython/blob/3.6/Python/peephole.c#L288) the implementation source for the same.\n",
@@ -2947,11 +2938,11 @@
"\n",
"When we initialize `row` variable, this visualization explains what happens in the memory\n",
"\n",
- "\n",
+ "\n",
"\n",
"And when the `board` is initialized by multiplying the `row`, this is what happens inside the memory (each of the elements `board[0]`, `board[1]` and `board[2]` is a reference to the same list referred by `row`)\n",
"\n",
- "\n",
+ "\n",
"\n",
"We can avoid this scenario here by not using `row` variable to generate `board`. (Asked in [this](https://github.com/satwikkansal/wtfpython/issues/68) issue).\n",
"\n"
@@ -13475,4 +13466,4 @@
"metadata": {},
"nbformat": 4,
"nbformat_minor": 2
-}
\ No newline at end of file
+}
diff --git a/noxfile.py b/noxfile.py
new file mode 100644
index 00000000..f693b854
--- /dev/null
+++ b/noxfile.py
@@ -0,0 +1,13 @@
+from typing import TYPE_CHECKING
+
+import nox
+
+
+if TYPE_CHECKING:
+ from nox.sessions import Session
+
+python_versions = ["3.9", "3.10", "3.11", "3.12", "3.13"]
+
+@nox.session(python=python_versions, reuse_venv=True)
+def tests(session: "Session") -> None:
+ _ = session.run("python", "snippets/2_tricky_strings.py")
diff --git a/poetry.lock b/poetry.lock
new file mode 100644
index 00000000..47b34986
--- /dev/null
+++ b/poetry.lock
@@ -0,0 +1,155 @@
+# This file is automatically @generated by Poetry 1.8.3 and should not be changed by hand.
+
+[[package]]
+name = "argcomplete"
+version = "3.5.1"
+description = "Bash tab completion for argparse"
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "argcomplete-3.5.1-py3-none-any.whl", hash = "sha256:1a1d148bdaa3e3b93454900163403df41448a248af01b6e849edc5ac08e6c363"},
+ {file = "argcomplete-3.5.1.tar.gz", hash = "sha256:eb1ee355aa2557bd3d0145de7b06b2a45b0ce461e1e7813f5d066039ab4177b4"},
+]
+
+[package.extras]
+test = ["coverage", "mypy", "pexpect", "ruff", "wheel"]
+
+[[package]]
+name = "colorama"
+version = "0.4.6"
+description = "Cross-platform colored terminal text."
+optional = false
+python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*,!=3.6.*,>=2.7"
+files = [
+ {file = "colorama-0.4.6-py2.py3-none-any.whl", hash = "sha256:4f1d9991f5acc0ca119f9d443620b77f9d6b33703e51011c16baf57afb285fc6"},
+ {file = "colorama-0.4.6.tar.gz", hash = "sha256:08695f5cb7ed6e0531a20572697297273c47b8cae5a63ffc6d6ed5c201be6e44"},
+]
+
+[[package]]
+name = "colorlog"
+version = "6.8.2"
+description = "Add colours to the output of Python's logging module."
+optional = false
+python-versions = ">=3.6"
+files = [
+ {file = "colorlog-6.8.2-py3-none-any.whl", hash = "sha256:4dcbb62368e2800cb3c5abd348da7e53f6c362dda502ec27c560b2e58a66bd33"},
+ {file = "colorlog-6.8.2.tar.gz", hash = "sha256:3e3e079a41feb5a1b64f978b5ea4f46040a94f11f0e8bbb8261e3dbbeca64d44"},
+]
+
+[package.dependencies]
+colorama = {version = "*", markers = "sys_platform == \"win32\""}
+
+[package.extras]
+development = ["black", "flake8", "mypy", "pytest", "types-colorama"]
+
+[[package]]
+name = "distlib"
+version = "0.3.9"
+description = "Distribution utilities"
+optional = false
+python-versions = "*"
+files = [
+ {file = "distlib-0.3.9-py2.py3-none-any.whl", hash = "sha256:47f8c22fd27c27e25a65601af709b38e4f0a45ea4fc2e710f65755fa8caaaf87"},
+ {file = "distlib-0.3.9.tar.gz", hash = "sha256:a60f20dea646b8a33f3e7772f74dc0b2d0772d2837ee1342a00645c81edf9403"},
+]
+
+[[package]]
+name = "filelock"
+version = "3.16.1"
+description = "A platform independent file lock."
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "filelock-3.16.1-py3-none-any.whl", hash = "sha256:2082e5703d51fbf98ea75855d9d5527e33d8ff23099bec374a134febee6946b0"},
+ {file = "filelock-3.16.1.tar.gz", hash = "sha256:c249fbfcd5db47e5e2d6d62198e565475ee65e4831e2561c8e313fa7eb961435"},
+]
+
+[package.extras]
+docs = ["furo (>=2024.8.6)", "sphinx (>=8.0.2)", "sphinx-autodoc-typehints (>=2.4.1)"]
+testing = ["covdefaults (>=2.3)", "coverage (>=7.6.1)", "diff-cover (>=9.2)", "pytest (>=8.3.3)", "pytest-asyncio (>=0.24)", "pytest-cov (>=5)", "pytest-mock (>=3.14)", "pytest-timeout (>=2.3.1)", "virtualenv (>=20.26.4)"]
+typing = ["typing-extensions (>=4.12.2)"]
+
+[[package]]
+name = "nox"
+version = "2024.10.9"
+description = "Flexible test automation."
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "nox-2024.10.9-py3-none-any.whl", hash = "sha256:1d36f309a0a2a853e9bccb76bbef6bb118ba92fa92674d15604ca99adeb29eab"},
+ {file = "nox-2024.10.9.tar.gz", hash = "sha256:7aa9dc8d1c27e9f45ab046ffd1c3b2c4f7c91755304769df231308849ebded95"},
+]
+
+[package.dependencies]
+argcomplete = ">=1.9.4,<4"
+colorlog = ">=2.6.1,<7"
+packaging = ">=20.9"
+tomli = {version = ">=1", markers = "python_version < \"3.11\""}
+virtualenv = ">=20.14.1"
+
+[package.extras]
+tox-to-nox = ["jinja2", "tox"]
+uv = ["uv (>=0.1.6)"]
+
+[[package]]
+name = "packaging"
+version = "24.1"
+description = "Core utilities for Python packages"
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "packaging-24.1-py3-none-any.whl", hash = "sha256:5b8f2217dbdbd2f7f384c41c628544e6d52f2d0f53c6d0c3ea61aa5d1d7ff124"},
+ {file = "packaging-24.1.tar.gz", hash = "sha256:026ed72c8ed3fcce5bf8950572258698927fd1dbda10a5e981cdf0ac37f4f002"},
+]
+
+[[package]]
+name = "platformdirs"
+version = "4.3.6"
+description = "A small Python package for determining appropriate platform-specific dirs, e.g. a `user data dir`."
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "platformdirs-4.3.6-py3-none-any.whl", hash = "sha256:73e575e1408ab8103900836b97580d5307456908a03e92031bab39e4554cc3fb"},
+ {file = "platformdirs-4.3.6.tar.gz", hash = "sha256:357fb2acbc885b0419afd3ce3ed34564c13c9b95c89360cd9563f73aa5e2b907"},
+]
+
+[package.extras]
+docs = ["furo (>=2024.8.6)", "proselint (>=0.14)", "sphinx (>=8.0.2)", "sphinx-autodoc-typehints (>=2.4)"]
+test = ["appdirs (==1.4.4)", "covdefaults (>=2.3)", "pytest (>=8.3.2)", "pytest-cov (>=5)", "pytest-mock (>=3.14)"]
+type = ["mypy (>=1.11.2)"]
+
+[[package]]
+name = "tomli"
+version = "2.0.2"
+description = "A lil' TOML parser"
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "tomli-2.0.2-py3-none-any.whl", hash = "sha256:2ebe24485c53d303f690b0ec092806a085f07af5a5aa1464f3931eec36caaa38"},
+ {file = "tomli-2.0.2.tar.gz", hash = "sha256:d46d457a85337051c36524bc5349dd91b1877838e2979ac5ced3e710ed8a60ed"},
+]
+
+[[package]]
+name = "virtualenv"
+version = "20.27.0"
+description = "Virtual Python Environment builder"
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "virtualenv-20.27.0-py3-none-any.whl", hash = "sha256:44a72c29cceb0ee08f300b314848c86e57bf8d1f13107a5e671fb9274138d655"},
+ {file = "virtualenv-20.27.0.tar.gz", hash = "sha256:2ca56a68ed615b8fe4326d11a0dca5dfbe8fd68510fb6c6349163bed3c15f2b2"},
+]
+
+[package.dependencies]
+distlib = ">=0.3.7,<1"
+filelock = ">=3.12.2,<4"
+platformdirs = ">=3.9.1,<5"
+
+[package.extras]
+docs = ["furo (>=2023.7.26)", "proselint (>=0.13)", "sphinx (>=7.1.2,!=7.3)", "sphinx-argparse (>=0.4)", "sphinxcontrib-towncrier (>=0.2.1a0)", "towncrier (>=23.6)"]
+test = ["covdefaults (>=2.3)", "coverage (>=7.2.7)", "coverage-enable-subprocess (>=1)", "flaky (>=3.7)", "packaging (>=23.1)", "pytest (>=7.4)", "pytest-env (>=0.8.2)", "pytest-freezer (>=0.4.8)", "pytest-mock (>=3.11.1)", "pytest-randomly (>=3.12)", "pytest-timeout (>=2.1)", "setuptools (>=68)", "time-machine (>=2.10)"]
+
+[metadata]
+lock-version = "2.0"
+python-versions = "^3.9"
+content-hash = "af91619c8e62e649ee538e51a248ef2fc1e4f4495e7748b3b551685aa47b404e"
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 00000000..a048fafe
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,16 @@
+[tool.poetry]
+name = "wtfpython"
+version = "3.0.0"
+description = "What the f*ck Python!"
+authors = ["Satwik Kansal "]
+license = "WTFPL 2.0"
+readme = "README.md"
+
+[tool.poetry.dependencies]
+python = "^3.9"
+nox = "^2024.10.9"
+
+
+[build-system]
+requires = ["poetry-core"]
+build-backend = "poetry.core.masonry.api"
diff --git a/snippets/2_tricky_strings.py b/snippets/2_tricky_strings.py
new file mode 100644
index 00000000..25320f27
--- /dev/null
+++ b/snippets/2_tricky_strings.py
@@ -0,0 +1,19 @@
+# 1
+assert id("some_string") == id("some" + "_" + "string")
+assert id("some_string") == id("some_string")
+
+# 2
+a = "wtf"
+b = "wtf"
+assert a is b
+
+a = "wtf!"
+b = "wtf!"
+assert a is b
+
+# 3
+a, b = "wtf!", "wtf!"
+assert a is b
+
+a = "wtf!"; b = "wtf!"
+assert a is b
diff --git a/wtfpython-pypi/wtf_python/__init__.py b/snippets/__init__.py
similarity index 100%
rename from wtfpython-pypi/wtf_python/__init__.py
rename to snippets/__init__.py
diff --git a/translations/fa-farsi/README.md b/translations/fa-farsi/README.md
new file mode 100644
index 00000000..cddeb0b7
--- /dev/null
+++ b/translations/fa-farsi/README.md
@@ -0,0 +1,4229 @@
+
+
+
+
+
+
+
+
+
+
+
What the f*ck Python! 😱
+
کاوش و درک پایتون از طریق تکههای کد شگفتانگیز.
+
+ترجمهها: [انگلیسی English](https://github.com/satwikkansal/wtfpython) | [چینی 中文](https://github.com/leisurelicht/wtfpython-cn) | [ویتنامی Tiếng Việt](https://github.com/vuduclyunitn/wtfptyhon-vi) | [اسپانیایی Español](https://web.archive.org/web/20220511161045/https://github.com/JoseDeFreitas/wtfpython-es) | [کرهای 한국어](https://github.com/buttercrab/wtfpython-ko) | [روسی Русский](https://github.com/satwikkansal/wtfpython/tree/master/translations/ru-russian) | [آلمانی Deutsch](https://github.com/BenSt099/wtfpython) | [Persian فارسی](https://github.com/satwikkansal/wtfpython/tree/master/translations/fa-farsi) | [اضافه کردن ترجمه](https://github.com/satwikkansal/wtfpython/issues/new?title=Add%20translation%20for%20[LANGUAGE]&body=Expected%20time%20to%20finish:%20[X]%20weeks.%20I%27ll%20start%20working%20on%20it%20from%20[Y].)
+
+حالتهای دیگر: [وبسایت تعاملی](https://wtfpython-interactive.vercel.app) | [دفترچه تعاملی](https://colab.research.google.com/github/satwikkansal/wtfpython/blob/master/irrelevant/wtf.ipynb)
+
+پایتون، یه زبان زیبا طراحی شده، سطح بالا و مبتنی بر مفسره که قابلیتهای بسیاری برای راحتی ما برنامهنویسها فراهم میکنه.
+ولی گاهی اوقات قطعهکدهایی رو میبینیم که تو نگاه اول خروجیهاشون واضح نیست.
+
+این یه پروژه باحاله که سعی داریم توش توضیح بدیم که پشت پرده یه سری قطعهکدهای غیرشهودی و قابلیتهای کمتر شناخته شده پایتون
+چه خبره.
+
+درحالی که بعضی از مثالهایی که قراره تو این سند ببینید واقعا عجیب و غریب نیستند ولی بخشهای جالبی از پایتون رو ظاهر میکنند که
+ممکنه شما از وجودشون بیخبر باشید. به نظرم این شیوه جالبیه برای یادگیری جزئیات داخلی یه زبان برنامه نویسی و باور دارم که
+برای شما هم جالب خواهد بود.
+
+اگه شما یه پایتون کار سابقهدار هستید، میتونید از این فرصت به عنوان یه چالش برای خودتون استفاده کنید تا بیشتر مثالها رو
+تو تلاش اول حدس بزنید. ممکنه شما بعضی از این مثالها رو قبلا تجربه کرده باشید و من خاطراتشون رو در این سند براتون زنده
+کرده باشم! :sweat_smile:
+
+پ.ن: اگه شما قبلا این سند رو خوندید، میتونید تغییرات جدید رو در بخش انتشار (فعلا در [اینجا](https://github.com/satwikkansal/wtfpython/releases/)) مطالعه کنید
+(مثالهایی که کنارشون علامت ستاره دارند، در آخرین ویرایش اضافه شدهاند).
+
+پس، بزن بریم...
+
+# فهرست مطالب
+
+
+
+
+
+- [فهرست مطالب](#فهرست-مطالب)
+- [ساختار مثالها](#ساختار-مثالها)
+- [استفاده](#استفاده)
+- [👀 مثالها](#-مثالها)
+ - [بخش: ذهن خود را به چالش بکشید!](#بخش-ذهن-خود-را-به-چالش-بکشید)
+ - [◀ اول از همه! \*](#-اول-از-همه-)
+ - [💡 توضیح](#-توضیح)
+ - [◀ بعضی وقتها رشتهها میتوانند دردسرساز شوند](#-بعضی-وقتها-رشتهها-میتوانند-دردسرساز-شوند)
+ - [💡 توضیح:](#-توضیح-1)
+ - [◀ مراقب عملیاتهای زنجیرهای باشید](#-مراقب-عملیاتهای-زنجیرهای-باشید)
+ - [💡 توضیح:](#-توضیح-2)
+ - [◀ چطور از عملگر `is` استفاده نکنیم](#-چطور-از-عملگر-is-استفاده-نکنیم)
+ - [💡 توضیح:](#-توضیح-3)
+ - [◀ کلیدهای هش](#-کلیدهای-هش)
+ - [💡 توضیح](#-توضیح-4)
+ - [◀ در عمق وجود همه ما یکسان هستیم](#-در-عمق-وجود-همه-ما-یکسان-هستیم)
+ - [💡 توضیح:](#-توضیح-5)
+ - [◀ بینظمی در خود نظم \*](#-بینظمی-در-خود-نظم-)
+ - [💡 توضیح:](#-توضیح-6)
+ - [💡 توضیح:](#-توضیح-7)
+ - [◀ برای چی؟](#-برای-چی)
+ - [💡 توضیح:](#-توضیح-8)
+ - [◀ اختلاف زمانی در محاسبه](#-اختلاف-زمانی-در-محاسبه)
+ - [💡 توضیح](#-توضیح-9)
+ - [◀ هر گردی، گردو نیست](#-هر-گردی-گردو-نیست)
+ - [💡 توضیح](#-توضیح-10)
+ - [◀ یک بازی دوز که توش X همون اول برنده میشه!](#-یک-بازی-دوز-که-توش-x-همون-اول-برنده-میشه)
+ - [💡 توضیح:](#-توضیح-11)
+ - [◀ متغیر شرودینگر \*](#-متغیر-شرودینگر-)
+ - [💡 توضیح:](#-توضیح-12)
+ - [◀ اول مرغ بوده یا تخم مرغ؟ \*](#-اول-مرغ-بوده-یا-تخم-مرغ-)
+ - [💡 توضیح](#-توضیح-13)
+ - [◀ روابط بین زیرمجموعه کلاسها](#-روابط-بین-زیرمجموعه-کلاسها)
+ - [💡 توضیح:](#-توضیح-14)
+ - [◀ برابری و هویت متدها](#-برابری-و-هویت-متدها)
+ - [💡 توضیح](#-توضیح-15)
+ - [◀ آل-ترو-یشن \*](#-آل-ترو-یشن-)
+ - [💡 توضیحات:](#-توضیحات)
+ - [💡 توضیح:](#-توضیح-16)
+ - [◀ رشتهها و بکاسلشها](#-رشتهها-و-بکاسلشها)
+ - [💡 توضیح:](#-توضیح-17)
+ - [◀ گره نیست، نَه!](#-گره-نیست-نَه)
+ - [💡 توضیح:](#-توضیح-18)
+ - [◀ رشتههای نیمه سهنقلقولی](#-رشتههای-نیمه-سهنقلقولی)
+ - [💡 توضیح:](#-توضیح-19)
+ - [◀ مشکل بولین ها چیست؟](#-مشکل-بولین-ها-چیست)
+ - [💡 توضیح:](#-توضیح-20)
+ - [◀ متغیرهای کلاس و متغیرهای نمونه](#-متغیرهای-کلاس-و-متغیرهای-نمونه)
+ - [💡 توضیح:](#-توضیح-21)
+ - [◀ واگذار کردن None](#-واگذار-کردن-none)
+ - [💡 توضیح:](#-توضیح-22)
+ - [◀ بازگرداندن با استفاده از `yield from`!](#-بازگرداندن-با-استفاده-از-yield-from)
+ - [💡 توضیح:](#-توضیح-23)
+ - [◀ بازتابناپذیری \*](#-بازتابناپذیری-)
+ - [💡 توضیح:](#-توضیح-24)
+ - [◀ تغییر دادن اشیای تغییرناپذیر!](#-تغییر-دادن-اشیای-تغییرناپذیر)
+ - [💡 توضیح:](#-توضیح-25)
+ - [◀ متغیری که از اسکوپ بیرونی ناپدید میشود](#-متغیری-که-از-اسکوپ-بیرونی-ناپدید-میشود)
+ - [💡 توضیح:](#-توضیح-26)
+ - [◀ تبدیل اسرارآمیز نوع کلید](#-تبدیل-اسرارآمیز-نوع-کلید)
+ - [💡 توضیح:](#-توضیح-27)
+ - [◀ ببینیم میتوانید این را حدس بزنید؟](#-ببینیم-میتوانید-این-را-حدس-بزنید)
+ - [💡 توضیح:](#-توضیح-28)
+ - [◀ از حد مجاز برای تبدیل رشته به عدد صحیح فراتر میرود](#-از-حد-مجاز-برای-تبدیل-رشته-به-عدد-صحیح-فراتر-میرود)
+ - [💡 توضیح:](#-توضیح-29)
+ - [بخش: شیبهای لغزنده](#بخش-شیبهای-لغزنده)
+ - [◀ تغییر یک دیکشنری هنگام پیمایش روی آن](#-تغییر-یک-دیکشنری-هنگام-پیمایش-روی-آن)
+ - [💡 توضیح:](#-توضیح-30)
+ - [◀ عملیات سرسختانهی `del`](#-عملیات-سرسختانهی-del)
+ - [💡 توضیح:](#-توضیح-31)
+ - [◀ متغیری که از حوزه خارج است](#-متغیری-که-از-حوزه-خارج-است)
+ - [💡 توضیح:](#-توضیح-32)
+ - [◀ حذف المانهای لیست در حین پیمایش](#-حذف-المانهای-لیست-در-حین-پیمایش)
+ - [💡 توضیح:](#-توضیح-33)
+ - [◀ زیپِ دارای اتلاف برای پیمایشگرها \*](#-زیپِ-دارای-اتلاف-برای-پیمایشگرها-)
+ - [💡 توضیح:](#-توضیح-34)
+ - [◀ نشت کردن متغیرهای حلقه!](#-نشت-کردن-متغیرهای-حلقه)
+ - [💡 توضیح:](#-توضیح-35)
+ - [◀ مراقب آرگومانهای تغییرپذیر پیشفرض باشید!](#-مراقب-آرگومانهای-تغییرپذیر-پیشفرض-باشید)
+ - [💡 توضیح:](#-توضیح-36)
+ - [◀ گرفتن استثناها (Exceptions)](#-گرفتن-استثناها-exceptions)
+ - [💡 توضیح](#-توضیح-37)
+ - [◀ عملوندهای یکسان، داستانی متفاوت!](#-عملوندهای-یکسان-داستانی-متفاوت)
+ - [💡 توضیح:](#-توضیح-38)
+ - [◀ تفکیک نامها با نادیده گرفتن حوزهی کلاس](#-تفکیک-نامها-با-نادیده-گرفتن-حوزهی-کلاس)
+ - [💡 توضیح](#-توضیح-39)
+ - [◀ گرد کردن به روش بانکدار \*](#-گرد-کردن-به-روش-بانکدار-)
+ - [💡 توضیح:](#-توضیح-40)
+ - [◀ سوزنهایی در انبار کاه \*](#-سوزنهایی-در-انبار-کاه-)
+ - [💡 توضیح:](#-توضیح-41)
+ - [◀ تقسیمها \*](#-تقسیمها-)
+ - [💡 توضیح:](#-توضیح-42)
+ - [◀ واردسازیهای عمومی \*](#-واردسازیهای-عمومی-)
+ - [💡 توضیح:](#-توضیح-43)
+ - [◀ همه چیز مرتب شده؟ \*](#-همه-چیز-مرتب-شده-)
+ - [💡 توضیح:](#-توضیح-44)
+ - [◀ زمان نیمهشب وجود ندارد؟](#-زمان-نیمهشب-وجود-ندارد)
+ - [💡 توضیح:](#-توضیح-45)
+ - [بخش: گنجینههای پنهان!](#بخش-گنجینههای-پنهان)
+ - [◀ خب پایتون، میتوانی کاری کنی پرواز کنم؟](#-خب-پایتون-میتوانی-کاری-کنی-پرواز-کنم)
+ - [💡 توضیح:](#-توضیح-46)
+ - [◀ `goto`، ولی چرا؟](#-goto-ولی-چرا)
+ - [💡 توضیح:](#-توضیح-47)
+ - [◀ خودتان را آماده کنید!](#-خودتان-را-آماده-کنید)
+ - [💡 توضیح:](#-توضیح-48)
+ - [◀ بیایید با «عمو زبان مهربان برای همیشه» آشنا شویم](#-بیایید-با-عمو-زبان-مهربان-برای-همیشه-آشنا-شویم)
+ - [💡 توضیح:](#-توضیح-49)
+ - [◀ حتی پایتون هم میداند که عشق پیچیده است](#-حتی-پایتون-هم-میداند-که-عشق-پیچیده-است)
+ - [💡 توضیح:](#-توضیح-50)
+ - [◀ بله، این واقعاً وجود دارد!](#-بله-این-واقعاً-وجود-دارد)
+ - [💡 توضیح:](#-توضیح-51)
+ - [◀ عملگر Ellipsis \*](#-عملگر-ellipsis-)
+ - [💡توضیح](#توضیح)
+ - [◀ بینهایت (`Inpinity`)](#-بینهایت-inpinity)
+ - [💡 توضیح:](#-توضیح-52)
+ - [◀ بیایید خرابکاری کنیم](#-بیایید-خرابکاری-کنیم)
+ - [💡 توضیح:](#-توضیح-53)
+ - [بخش: ظاهرها فریبندهاند!](#بخش-ظاهرها-فریبندهاند)
+ - [◀ خطوط را رد میکند؟](#-خطوط-را-رد-میکند)
+ - [💡 توضیح](#-توضیح-54)
+ - [◀ تلهپورت کردن](#-تلهپورت-کردن)
+ - [💡 توضیح:](#-توضیح-55)
+ - [◀ خب، یک جای کار مشکوک است...](#-خب-یک-جای-کار-مشکوک-است)
+ - [💡 توضیح](#-توضیح-56)
+ - [بخش: متفرقه](#بخش-متفرقه)
+ - [◀ `+=` سریعتر است](#--سریعتر-است)
+ - [💡 توضیح:](#-توضیح-57)
+ - [◀ بیایید یک رشتهی بزرگ بسازیم!](#-بیایید-یک-رشتهی-بزرگ-بسازیم)
+ - [💡 توضیح](#-توضیح-58)
+ - [◀ کُند کردن جستجوها در `dict` \*](#-کُند-کردن-جستجوها-در-dict-)
+ - [💡 توضیح:](#-توضیح-59)
+ - [◀ حجیم کردن دیکشنری نمونهها (`instance dicts`) \*](#-حجیم-کردن-دیکشنری-نمونهها-instance-dicts-)
+ - [💡 توضیح:](#-توضیح-60)
+ - [◀ موارد جزئی \*](#-موارد-جزئی-)
+- [مشارکت](#مشارکت)
+- [تقدیر و تشکر](#تقدیر-و-تشکر) - [چند لینک جالب!](#چند-لینک-جالب)
+- [🎓 مجوز](#-مجوز)
+ - [دوستانتان را هم شگفتزده کنید!](#دوستانتان-را-هم-شگفتزده-کنید)
+ - [آیا به یک نسخه pdf نیاز دارید؟](#آیا-به-یک-نسخه-pdf-نیاز-دارید)
+
+
+
+# ساختار مثالها
+
+همه مثالها به صورت زیر ساخته میشوند:
+
+> ### ◀ یه اسم خوشگل
+>
+> ```py
+> # راه اندازی کد
+> # آماده سازی برای جادو...
+> ```
+>
+> **خروجی (نسخه(های) پایتون):**
+>
+> ```py
+> >>> triggering_statement
+> یه خروجی غیرمنتظره
+> ```
+>
+> (دلخواه): توضیح یکخطی خروجی غیرمنتظره
+>
+> #### 💡 توضیح:
+>
+> - توضیح کوتاه درمورد اینکه چی داره اتفاق میافته و چرا.
+>
+> ```py
+> # راه اندازی کد
+> # مثالهای بیشتر برای شفاف سازی (در صورت نیاز)
+> ```
+>
+> **خروجی (نسخه(های) پایتون):**
+>
+> ```py
+> >>> trigger # یک مثال که رونمایی از جادو رو راحتتر میکنه
+> # یک خروجی توجیه شده و واضح
+> ```
+
+**توجه:** همه مثالها در برنامه مفسر تعاملی پایتون نسخه
+۳.۵.۲ آزمایش شدهاند و باید در همه نسخههای پایتون کار
+کنند مگراینکه به صورت جداگانه و به طور واضح نسخه مخصوص
+پایتون قبل از خروجی ذکر شده باشد.
+
+# استفاده
+
+یه راه خوب برای بیشتر بهره بردن، به نظرم، اینه که مثالها رو به ترتیب متوالی بخونید و برای هر مثال:
+
+- کد ابتدایی برای راه اندازی مثال رو با دقت بخونید. اگه شما یه پایتون کار سابقهدار باشید، با موفقیت بیشتر اوقات اتفاق بعدی رو پیشبینی میکنید.
+- قطعه خروجی رو بخونید و
+ - بررسی کنید که آیا خروجیها همونطور که انتظار دارید هستند.
+ - مطمئین بشید که دقیقا دلیل اینکه خروجی اون طوری هست رو میدونید.
+ - اگه نمیدونید (که کاملا عادیه و اصلا بد نیست)، یک نفس عمیق بکشید و توضیحات رو بخونید (و اگه نفهمیدید، داد بزنید! و [اینجا](https://github.com/emargi/wtfpython/issues/new) درموردش حرف بزنید).
+ - اگه میدونید، به افتخار خودتون یه دست محکم بزنید و برید سراغ مثال بعدی.
+
+---
+
+# 👀 مثالها
+
+## بخش: ذهن خود را به چالش بکشید!
+
+### ◀ اول از همه! \*
+
+
+
+
+به دلایلی، عملگر "Walrus" (`:=`) که در نسخه ۳.۸ پایتون معرفی شد، خیلی محبوب شده. بیاید بررسیش کنیم.
+
+1\.
+
+```py
+# Python version 3.8+
+
+>>> a = "wtf_walrus"
+>>> a
+'wtf_walrus'
+
+>>> a := "wtf_walrus"
+File "", line 1
+ a := "wtf_walrus"
+ ^
+SyntaxError: invalid syntax
+
+>>> (a := "wtf_walrus") # ولی این کار میکنه
+'wtf_walrus'
+>>> a
+'wtf_walrus'
+```
+
+2 \.
+
+```py
+# Python version 3.8+
+
+>>> a = 6, 9
+>>> a
+(6, 9)
+
+>>> (a := 6, 9)
+(6, 9)
+>>> a
+6
+
+>>> a, b = 6, 9 # باز کردن معمولی
+>>> a, b
+(6, 9)
+>>> (a, b = 16, 19) # آخ آخ
+ File "", line 1
+ (a, b = 16, 19)
+ ^
+SyntaxError: invalid syntax
+
+>>> (a, b := 16, 19) # این یه تاپل ۳تایی چاپ میکنه رو صفحه
+(6, 16, 19)
+
+>>> a # هنوز تغییر نکرده؟
+6
+
+>>> b
+16
+```
+
+#### 💡 توضیح
+
+**مرور سریع بر عملگر Walrus**
+
+عملگر Walrus همونطور که اشاره شد، در نسخه ۳.۸ پایتون معرفی
+شد. این عملگر میتونه تو موقعیتهایی کاربردی باشه که شما میخواید داخل یه عبارت، مقادیری رو به متغیرها اختصاص بدید.
+
+```py
+def some_func():
+ # فرض کنید اینجا یک سری محاسبه سنگین انجام میشه
+ # time.sleep(1000)
+ return 5
+
+# پس به جای اینکه این کارو بکنید:
+if some_func():
+ print(some_func()) # که خیلی راه نادرستیه چون محاسبه دوبار انجام میشه
+
+# یا حتی این کارو کنید (که کار بدی هم نیست)
+a = some_func()
+if a:
+ print(a)
+
+# میتونید از این به بعد به طور مختصر بنویسید:
+if a := some_func():
+ print(a)
+
+```
+
+**خروجی (+۳.۸):**
+
+```py
+5
+5
+5
+```
+
+این باعث میشه که یک خط کمتر کد بزنیم و از دوبار فراخوندن `some_func` جلوگیری کرد.
+
+- "عبارت اختصاصدادن مقدار" بدون پرانتز (نحوه استفاده عملگر Walrus)، در سطح بالا محدود است، `SyntaxError` در عبارت `a := "wtf_walrus"` در قطعهکد اول به همین دلیل است. قرار دادن آن داخل پرانتز، همانطور که میخواستیم کار کرد و مقدار را به `a` اختصاص داد.
+
+- به طور معمول، قرار دادن عبارتی که دارای `=` است داخل پرانتز مجاز نیست. به همین دلیل عبارت `(a, b = 6, 9)` به ما خطای سینتکس داد.
+
+- قائده استفاده از عملگر Walrus به صورت `NAME:= expr` است، به طوری که `NAME` یک شناسه صحیح و `expr` یک عبارت صحیح است. به همین دلیل باز و بسته کردن با تکرار (iterable) پشتیبانی نمیشوند. پس،
+
+ - عبارت `(a := 6, 9)` معادل عبارت `((a := 6), 9)` و در نهایت `(a, 9)` است. (که مقدار `a` عدد 6 است)
+
+ ```py
+ >>> (a := 6, 9) == ((a := 6), 9)
+ True
+ >>> x = (a := 696, 9)
+ >>> x
+ (696, 9)
+ >>> x[0] is a # هر دو به یک مکان در حافظه دستگاه اشاره میکنند
+ True
+ ```
+
+ - به طور مشابه، عبارت `(a, b := 16, 19)` معادل عبارت `(a, (b := 16), 19)` است که چیزی جز یک تاپل ۳تایی نیست.
+
+---
+
+### ◀ بعضی وقتها رشتهها میتوانند دردسرساز شوند
+
+
+
+1\.
+
+```py
+>>> a = "some_string"
+>>> id(a)
+140420665652016
+>>> id("some" + "_" + "string") # دقت کنید که هردو شناسه یکسانند.
+140420665652016
+```
+
+2\.
+
+```py
+>>> a = "wtf"
+>>> b = "wtf"
+>>> a is b
+True
+
+>>> a = "wtf!"
+>>> b = "wtf!"
+>>> a is b
+False
+
+```
+
+3\.
+
+```py
+>>> a, b = "wtf!", "wtf!"
+>>> a is b # همهی نسخهها به جز 3.7.x
+True
+
+>>> a = "wtf!"; b = "wtf!"
+>>> a is b # ممکن است True یا False باشد بسته به جایی که آن را اجرا میکنید (python shell / ipython / بهصورت اسکریپت)
+False
+```
+
+```py
+# این بار در فایل some_file.py
+a = "wtf!"
+b = "wtf!"
+print(a is b)
+
+# موقع اجرای ماژول، True را چاپ میکند!
+```
+
+4\.
+
+**خروجی (< Python3.7 )**
+
+```py
+>>> 'a' * 20 is 'aaaaaaaaaaaaaaaaaaaa'
+True
+>>> 'a' * 21 is 'aaaaaaaaaaaaaaaaaaaaa'
+False
+```
+
+منطقیه، نه؟
+
+#### 💡 توضیح:
+
+- در قطعهکد اول و دوم، رفتار کد به دلیل یک بهینه سازی در CPython است (به نام داوطلب سازی رشتهها) که باعث میشود از برخی مقادیر غیرقابل تغییر، به جای مقداردهی مجدد، دوباره استفاده شود.
+- بیشتر متغیرهایی که بهاین صورت جایگزین میشوند، در حافظه دستگاه به مقدار داوطلب خود اشاره میکنند (تا از حافظه کمتری استفاده شود)
+- در قطعهکدهای بالا، رشتهها بهصورت غیرمستقیم داوطلب میشوند. تصمیم اینکه رشتهها چه زمانی به صورت غیرمستقیم داوطلب شوند به نحوه پیادهسازی و مقداردهی آنها بستگی دارد. برخی قوانین وجود دارند تا بتوانیم داوطلب شدن یا نشدن یک رشته را حدس بزنیم:
+ - همه رشتهها با طول صفر یا یک داوطلب میشوند.
+ - رشتهها در زمان کامپایل داوطلب میشوند (`'wtf'` داوطلب میشود اما `''.join(['w', 't', 'f'])` داوطلب نمیشود)
+ - رشتههایی که از حروف ASCII ، اعداد صحیح و آندرلاین تشکیل نشدهباشند داوطلب نمیشود. به همین دلیل `'wtf!'` به خاطر وجود `'!'` داوطلب نشد. پیادهسازی این قانون در CPython در [اینجا](https://github.com/python/cpython/blob/3.6/Objects/codeobject.c#L19) قرار دارد.
+
+
+
+
+
+
+
+
+
+- زمانی که `"wtf!"` را در یک خط به `a` و `b` اختصاص میدهیم، مفسر پایتون شیء جدید میسازد و متغیر دوم را به آن ارجاع میدهد. اگر مقدار دهی در خطهای جدا از هم انجام شود، در واقع مفسر "خبر ندارد" که یک شیء مختص به `"wtf!"` از قبل در برنامه وجود دارد (زیرا `"wtf!"` به دلایلی که در بالا گفته شد، بهصورت غیرمستقیم داوطلب نمیشود). این بهینه سازی در زمان کامپایل انجام میشود. این بهینه سازی همچنین برای نسخه های (x).۳.۷ وجود ندارد (برای گفتوگوی بیشتر این [موضوع](https://github.com/satwikkansal/wtfpython/issues/100) را ببینید).
+- یک واحد کامپایل در یک محیط تعاملی مانند IPython از یک عبارت تشکیل میشود، در حالی که برای ماژولها شامل کل ماژول میشود. `a, b = "wtf!", "wtf!"` یک عبارت است. در حالی که `a = "wtf!"; b = "wtf!"` دو عبارت در یک خط است. به همین دلیل شناسهها در `a = "wtf!"; b = "wtf!"` متفاوتند و همینطور وقتی با مفسر پایتون داخل فایل `some_file.py` اجرا میشوند، شناسهها یکسانند.
+- تغییر ناگهانی در خروجی قطعهکد چهارم به دلیل [بهینهسازی پنجرهای](https://en.wikipedia.org/wiki/Peephole_optimization) است که تکنیکی معروف به جمع آوری ثابتها است. به همین خاطر عبارت `'a'*20` با `'aaaaaaaaaaaaaaaaaaaa'` در هنگام کامپایل جایگزین میشود تا کمی بار از دوش چرخهساعتی پردازنده کم شود. تکنیک جمع آوری ثابتها فقط مخصوص رشتههایی با طول کمتر از 21 است. (چرا؟ فرض کنید که فایل `.pyc` که توسط کامپایلر ساخته میشود چقدر بزرگ میشد اگر عبارت `'a'*10**10`). [این](https://github.com/python/cpython/blob/3.6/Python/peephole.c#L288) هم کد پیادهسازی این تکنیک در CPython.
+- توجه: در پایتون ۳.۷، جمع آوری ثابتها از بهینهساز پنجرهای به بهینهساز AST جدید انتقال داده شد همراه با تغییراتی در منطق آن. پس چهارمین قطعهکد در پایتون نسخه ۳.۷ کار نمیکند. شما میتوانید در [اینجا](https://bugs.python.org/issue11549) بیشتر درمورد این تغییرات بخوانید.
+
+---
+
+### ◀ مراقب عملیاتهای زنجیرهای باشید
+
+
+
+```py
+>>> (False == False) in [False] # منطقیه
+False
+>>> False == (False in [False]) # منطقیه
+False
+>>> False == False in [False] # حالا چی؟
+True
+
+>>> True is False == False
+False
+>>> False is False is False
+True
+
+>>> 1 > 0 < 1
+True
+>>> (1 > 0) < 1
+False
+>>> 1 > (0 < 1)
+False
+```
+
+#### 💡 توضیح:
+
+طبق https://docs.python.org/3/reference/expressions.html#comparisons
+
+> اگر a، b، c، ...، y، z عبارتهای عملیات و op1، op2، ...، opN عملگرهای عملیات باشند، آنگاه عملیات a op1 b op2 c ... y opN z معادل عملیات a op1 b and b op2 c and ... y opN z است. فقط دقت کنید که هر عبارت یک بار ارزیابی میشود.
+
+شاید چنین رفتاری برای شما احمقانه به نظر بیاد ولی برای عملیاتهایی مثل `a == b == c` و `0 <= x <= 100` عالی عمل میکنه.
+
+- عبارت `False is False is False` معادل عبارت `(False is False) and (False is False)` است
+- عبارت `True is False == False` معادل عبارت `(True is False) and (False == False)` است و از آنجایی که قسمت اول این عبارت (`True is False`) پس از ارزیابی برابر با `False` میشود. پس کل عبارت معادل `False` میشود.
+- عبارت `1 > 0 < 1` معادل عبارت `(1 > 0) and (0 < 1)` است.
+- عبارت `(1 > 0) < 1` معادل عبارت `True < 1` است و :
+
+ ```py
+ >>> int(True)
+ 1
+ >>> True + 1 # مربوط به این بخش نیست ولی همینجوری گذاشتم
+ 2
+ ```
+
+ پس عبارت `True < 1` معادل عبارت `1 < 1` میشود که در کل معادل `False` است.
+
+---
+
+### ◀ چطور از عملگر `is` استفاده نکنیم
+
+
+
+عبارت پایین خیلی معروفه و تو کل اینترنت موجوده.
+
+1\.
+
+```py
+>>> a = 256
+>>> b = 256
+>>> a is b
+True
+
+>>> a = 257
+>>> b = 257
+>>> a is b
+False
+```
+
+2\.
+
+```py
+>>> a = []
+>>> b = []
+>>> a is b
+False
+
+>>> a = tuple()
+>>> b = tuple()
+>>> a is b
+True
+```
+
+3\.
+**خروجی**
+
+```py
+>>> a, b = 257, 257
+>>> a is b
+True
+```
+
+**خروجی (مخصوص نسخههای (x).۳.۷)**
+
+```py
+>>> a, b = 257, 257
+>>> a is b
+False
+```
+
+#### 💡 توضیح:
+
+**فرض بین عملگرهای `is` و `==`**
+
+- عملگر `is` بررسی میکنه که دو متغیر در حافظه دستگاه به یک شیء اشاره میکنند یا نه (یعنی شناسه متغیرها رو با هم تطبیق میده).
+- عملگر `==` مقدار متغیرها رو با هم مقایسه میکنه و یکسان بودنشون رو بررسی میکنه.
+- پس `is` برای معادل بودن متغیرها در حافظه دستگاه و `==` برای معادل بودن مقادیر استفاده میشه. یه مثال برای شفاف سازی بیشتر:
+
+ ```py
+ >>> class A: pass
+ >>> A() is A() # اینها دو شیء خالی هستند که در دو جای مختلف در حافظه قرار دارند.
+ False
+ ```
+
+**عدد `256` از قبل تو حافظه قرار داده شده ولی `257` نه؟**
+
+وقتی پایتون رو اجرا میکنید اعداد از `-5` تا `256` در حافظه ذخیره میشن. چون این اعداد خیلی پرکاربرد هستند پس منطقیه که اونها رو در حافظه دستگاه، آماده داشته باشیم.
+
+نقل قول از https://docs.python.org/3/c-api/long.html
+
+> در پیاده سازی فعلی یک آرایه از اشیاء عددی صحیح برای تمام اعداد صحیح بین `-5` تا `256` نگهداری میشود. وقتی شما یک عدد صحیح در این بازه به مقداردهی میکنید، فقط یک ارجاع به آن عدد که از قبل در حافظه ذخیره شده است دریافت میکنید. پس تغییر مقدار عدد 1 باید ممکن باشد. که در این مورد من به رفتار پایتون شک دارم تعریفنشده است. :-)
+
+```py
+>>> id(256)
+10922528
+>>> a = 256
+>>> b = 256
+>>> id(a)
+10922528
+>>> id(b)
+10922528
+>>> id(257)
+140084850247312
+>>> x = 257
+>>> y = 257
+>>> id(x)
+140084850247440
+>>> id(y)
+140084850247344
+```
+
+در اینجا مفسر وقتی عبارت `y = 257` رو اجرا میکنه، به اندازه کافی زیرکانه عمل نمیکنه که تشخیص بده که ما یک عدد صحیح با مقدار `257` در حافظه ذخیره کردهایم، پس به ساختن یک شیء جدید در حافظه ادامه میده.
+
+یک بهینه سازی مشابه شامل حال مقادیر **غیرقابل تغییر** دیگه مانند تاپلهای خالی هم میشه. از اونجایی که لیستها قابل تغییرند، عبارت `[] is []` مقدار `False` رو برمیگردونه و عبارت `() is ()` مقدار `True` رو برمیگردونه. به همین دلیله که قطعه کد دوم چنین رفتاری داره. بریم سراغ سومی.
+
+**متغیرهای `a` و `b` وقتی در یک خط با مقادیر یکسانی مقداردهی میشن، هردو به یک شیء در حافظه اشاره میکنن**
+
+**خروجی**
+
+```py
+>>> a, b = 257, 257
+>>> id(a)
+140640774013296
+>>> id(b)
+140640774013296
+>>> a = 257
+>>> b = 257
+>>> id(a)
+140640774013392
+>>> id(b)
+140640774013488
+```
+
+- وقتی a و b در یک خط با `257` مقداردهی میشن، مفسر پایتون یک شیء برای یکی از متغیرها در حافظه میسازه و متغیر دوم رو در حافظه به اون ارجاع میده. اگه این کار رو تو دو خط جدا از هم انجام بدید، درواقع مفسر پایتون از وجود مقدار `257` به عنوان یک شیء، "خبر نداره".
+
+- این یک بهینه سازی توسط کامپایلر هست و مخصوصا در محیط تعاملی به کار برده میشه. وقتی شما دو خط رو در یک مفسر زنده وارد میکنید، اونها به صورت جداگانه کامپایل میشن، به همین دلیل بهینه سازی به صورت جداگانه برای هرکدوم اعمال میشه. اگر بخواهید این مثال رو در یک فایل `.py` امتحان کنید، رفتار متفاوتی میبینید زیرا فایل به صورت کلی و یکجا کامپایل میشه. این بهینه سازی محدود به اعداد صحیح نیست و برای انواع دادههای غیرقابل تغییر دیگه مانند رشتهها (مثال "رشتهها میتوانند دردسرساز شوند" رو ببینید) و اعداد اعشاری هم اعمال میشه.
+
+ ```py
+ >>> a, b = 257.0, 257.0
+ >>> a is b
+ True
+ ```
+
+- چرا این برای پایتون ۳.۷ کار نکرد؟ دلیل انتزاعیش اینه که چنین بهینهسازیهای کامپایلری وابسته به پیادهسازی هستن (یعنی بسته به نسخه، و نوع سیستمعامل و چیزهای دیگه تغییر میکنن). من هنوز پیگیرم که بدونم که کدوم تغییر تو پیادهسازی باعث همچین مشکلاتی میشه، میتونید برای خبرهای بیشتر این [موضوع](https://github.com/satwikkansal/wtfpython/issues/100) رو نگاه کنید.
+
+---
+
+### ◀ کلیدهای هش
+
+
+
+1\.
+
+```py
+some_dict = {}
+some_dict[5.5] = "JavaScript"
+some_dict[5.0] = "Ruby"
+some_dict[5] = "Python"
+```
+
+**خروجی:**
+
+```py
+>>> some_dict[5.5]
+"JavaScript"
+>>> some_dict[5.0] # رشته ("Python")، رشته ("Ruby") رو از بین برد؟
+"Python"
+>>> some_dict[5]
+"Python"
+
+>>> complex_five = 5 + 0j
+>>> type(complex_five)
+complex
+>>> some_dict[complex_five]
+"Python"
+```
+
+خب، چرا Python همه جارو گرفت؟
+
+#### 💡 توضیح
+
+- تو دیکشنریهای پایتون چیزی که کلیدها رو یگانه میکنه مقدار کلیدهاست، نه شناسه اونها. پس با اینکه `5`، `5.0` و `5 + 0j` شیءهای متمایزی از نوعهای متفاوتی هستند ولی از اون جایی که مقدارشون با هم برابره، نمیتونن داخل یه `dict` به عنوان کلید جدا از هم باشن (حتی به عنوان مقادیر داخل یه `set` نمیتونن باشن). وقتی بخواید داخل یه دیکشنری جستوجو کنید، به محض اینکه یکی از این دادهها رو وارد کنید، مقدار نگاشتهشده به کلیدی که مقدار برابر با اون داده داره ولی نوعش متفاوته، با موفقیت برگردونده میشه (به جای اینکه به ارور `KeyError` بردخورد کنید.).
+
+ ```py
+ >>> 5 == 5.0 == 5 + 0j
+ True
+ >>> 5 is not 5.0 is not 5 + 0j
+ True
+ >>> some_dict = {}
+ >>> some_dict[5.0] = "Ruby"
+ >>> 5.0 in some_dict
+ True
+ >>> (5 in some_dict) and (5 + 0j in some_dict)
+ True
+ ```
+
+- همچنین این قانون برای مقداردهی توی دیکشنری هم اعمال میشه. وقتی شما عبارت `some_dict[5] = "Python"` رو اجرا میکنید، پایتون دنبال کلیدی با مقدار یکسان میگرده که اینجا ما داریم `5.0 -> "Ruby"` و مقدار نگاشتهشده به این کلید در دیکشنری رو با مقدار جدید جایگزین میکنه و کلید رو همونجوری که هست باقی میذاره.
+
+ ```py
+ >>> some_dict
+ {5.0: 'Ruby'}
+ >>> some_dict[5] = "Python"
+ >>> some_dict
+ {5.0: 'Python'}
+ ```
+
+- خب پس چطوری میتونیم مقدار خود کلید رو به `5` تغییر بدیم (جای `5.0`)؟ راستش ما نمیتونیم این کار رو درجا انجام بدیم، ولی میتونیم اول اون کلید رو پاک کنیم (`del some_dict[5.0]`) و بعد کلیدی که میخوایم رو قرار بدیم (`some_dict[5]`) تا بتونیم عدد صحیح `5` رو به جای عدد اعشاری `5.0` به عنوان کلید داخل دیکشنری داشته باشیم. درکل خیلی کم پیش میاد که بخوایم چنین کاری کنیم.
+
+- پایتون چطوری توی دیکشنری که کلید `5.0` رو داره، کلید `5` رو پیدا کرد؟ پایتون این کار رو توی زمان ثابتی توسط توابع هش انجام میده بدون اینکه مجبور باشه همه کلیدها رو بررسی کنه. وقتی پایتون دنبال کلیدی مثل `foo` داخل یه `dict` میگرده، اول مقدار `hash(foo)` رو محاسبه میکنه (که توی زمان ثابتی انجام میشه). از اونجایی که توی پایتون برای مقایسه برابری مقدار دو شیء لازمه که هش یکسانی هم داشته باشند ([مستندات](https://docs.python.org/3/reference/datamodel.html#object.__hash__)). `5`، `5.0` و `5 + 0j` مقدار هش یکسانی دارند.
+
+ ```py
+ >>> 5 == 5.0 == 5 + 0j
+ True
+ >>> hash(5) == hash(5.0) == hash(5 + 0j)
+ True
+ ```
+
+ **توجه:** برعکس این قضیه لزوما درست نیست. شیءهای میتونن هش های یکسانی داشته باشند ولی مقادیر نابرابری داشته باشند. (این باعث به وجود اومدن پدیدهای معروف [تصادف هش]() میشه)، در این صورت توابع هش عملکرد خودشون رو کندتر از حالت عادی انجام میدهند.
+
+---
+
+### ◀ در عمق وجود همه ما یکسان هستیم
+
+
+
+```py
+class WTF:
+ pass
+```
+
+**خروجی:**
+
+```py
+>>> WTF() == WTF() # دو نمونه متفاوت از یک کلاس نمیتونند برابر هم باشند
+False
+>>> WTF() is WTF() # شناسهها هم متفاوتند
+False
+>>> hash(WTF()) == hash(WTF()) # هشها هم _باید_ متفاوت باشند
+True
+>>> id(WTF()) == id(WTF())
+True
+```
+
+#### 💡 توضیح:
+
+- وقتی `id` صدا زده شد، پایتون یک شیء با کلاس `WTF` ساخت و اون رو به تابع `id` داد. تابع `id` شناسه این شیء رو میگیره (درواقع آدرس اون شیء در حافظه دستگاه) و شیء رو حذف میکنه.
+- وقتی این کار رو دو بار متوالی انجام بدیم، پایتون آدرس یکسانی رو به شیء دوم اختصاص میده. از اونجایی که (در CPython) تابع `id` از آدرس شیءها توی حافظه به عنوان شناسه برای اونها استفاده میکنه، پس شناسه این دو شیء یکسانه.
+- پس، شناسه یک شیء تا زمانی که اون شیء وجود داره، منحصربهفرده. بعد از اینکه اون شیء حذف میشه یا قبل از اینکه اون شیء به وجود بیاد، چیز دیگهای میتونه اون شناسه رو داشته باشه.
+- ولی چرا با عملگر `is` مقدار `False` رو دریافت کردیم؟ بیاید با یه قطعهکد ببینیم دلیلش رو.
+
+ ```py
+ class WTF(object):
+ def __init__(self): print("I")
+ def __del__(self): print("D")
+ ```
+
+ **خروجی:**
+
+ ```py
+ >>> WTF() is WTF()
+ I
+ I
+ D
+ D
+ False
+ >>> id(WTF()) == id(WTF())
+ I
+ D
+ I
+ D
+ True
+ ```
+
+ همونطور که مشاهده میکنید، ترتیب حذف شدن شیءها باعث تفاوت میشه.
+
+---
+
+### ◀ بینظمی در خود نظم \*
+
+
+
+```py
+from collections import OrderedDict
+
+dictionary = dict()
+dictionary[1] = 'a'; dictionary[2] = 'b';
+
+ordered_dict = OrderedDict()
+ordered_dict[1] = 'a'; ordered_dict[2] = 'b';
+
+another_ordered_dict = OrderedDict()
+another_ordered_dict[2] = 'b'; another_ordered_dict[1] = 'a';
+
+class DictWithHash(dict):
+ """
+ یک dict که تابع جادویی __hash__ هم توش پیاده شده.
+ """
+ __hash__ = lambda self: 0
+
+class OrderedDictWithHash(OrderedDict):
+ """
+ یک OrderedDict که تابع جادویی __hash__ هم توش پیاده شده.
+ """
+ __hash__ = lambda self: 0
+```
+
+**خروجی**
+
+```py
+>>> dictionary == ordered_dict # اگر مقدار اولی با دومی برابره
+True
+>>> dictionary == another_ordered_dict # و مقدار اولی با سومی برابره
+True
+>>> ordered_dict == another_ordered_dict # پس چرا مقدار دومی با سومی برابر نیست؟
+False
+
+# ما همهمون میدونیم که یک مجموعه فقط شامل عناصر منحصربهفرد و غیرتکراریه.
+# بیاید یک مجموعه از این دیکشنریها بسازیم ببینیم چه اتفاقی میافته...
+
+>>> len({dictionary, ordered_dict, another_ordered_dict})
+Traceback (most recent call last):
+ File "", line 1, in
+TypeError: unhashable type: 'dict'
+
+# منطقیه چون dict ها __hash__ توشون پیادهسازی نشده. پس بیاید از
+# کلاسهایی که خودمون درست کردیم استفاده کنیم.
+>>> dictionary = DictWithHash()
+>>> dictionary[1] = 'a'; dictionary[2] = 'b';
+>>> ordered_dict = OrderedDictWithHash()
+>>> ordered_dict[1] = 'a'; ordered_dict[2] = 'b';
+>>> another_ordered_dict = OrderedDictWithHash()
+>>> another_ordered_dict[2] = 'b'; another_ordered_dict[1] = 'a';
+>>> len({dictionary, ordered_dict, another_ordered_dict})
+1
+>>> len({ordered_dict, another_ordered_dict, dictionary}) # ترتیب رو عوض میکنیم
+2
+```
+
+چی شد؟
+
+#### 💡 توضیح:
+
+- دلیل اینکه این مقایسه بین متغیرهای `dictionary`، `ordered_dict` و `another_ordered_dict` به درستی اجرا نمیشه به خاطر نحوه پیادهسازی تابع `__eq__` در کلاس `OrderedDict` هست. طبق [مستندات](https://docs.python.org/3/library/collections.html#ordereddict-objects)
+ > مقایسه برابری بین شیءهایی از نوع OrderedDict به ترتیب اعضای آنها هم بستگی دارد و به صورت `list(od1.items())==list(od2.items())` پیاده سازی شده است. مقایسه برابری بین شیءهای `OrderedDict` و شیءهای قابل نگاشت دیگر به ترتیب اعضای آنها بستگی ندارد و مقایسه همانند دیکشنریهای عادی انجام میشود.
+- این رفتار باعث میشه که بتونیم `OrderedDict` ها رو هرجایی که یک دیکشنری عادی کاربرد داره، جایگزین کنیم و استفاده کنیم.
+- خب، حالا چرا تغییر ترتیب روی طول مجموعهای که از دیکشنریها ساختیم، تاثیر گذاشت؟ جوابش همین رفتار مقایسهای غیرانتقالی بین این شیءهاست. از اونجایی که `set` ها مجموعهای از عناصر غیرتکراری و بدون نظم هستند، ترتیبی که عناصر تو این مجموعهها درج میشن نباید مهم باشه. ولی در این مورد، مهم هست. بیاید کمی تجزیه و تحلیلش کنیم.
+
+ ```py
+ >>> some_set = set()
+ >>> some_set.add(dictionary) # این شیءها از قطعهکدهای بالا هستند.
+ >>> ordered_dict in some_set
+ True
+ >>> some_set.add(ordered_dict)
+ >>> len(some_set)
+ 1
+ >>> another_ordered_dict in some_set
+ True
+ >>> some_set.add(another_ordered_dict)
+ >>> len(some_set)
+ 1
+
+ >>> another_set = set()
+ >>> another_set.add(ordered_dict)
+ >>> another_ordered_dict in another_set
+ False
+ >>> another_set.add(another_ordered_dict)
+ >>> len(another_set)
+ 2
+ >>> dictionary in another_set
+ True
+ >>> another_set.add(another_ordered_dict)
+ >>> len(another_set)
+ 2
+ ```
+
+ پس بیثباتی تو این رفتار به خاطر اینه که مقدار `another_ordered_dict in another_set` برابر با `False` هست چون `ordered_dict` از قبل داخل `another_set` هست و همونطور که قبلا مشاهده کردید، مقدار `ordered_dict == another_ordered_dict` برابر با `False` هست.
+
+---
+
+### ◀ تلاش کن... \*
+
+
+
+```py
+def some_func():
+ try:
+ return 'from_try'
+ finally:
+ return 'from_finally'
+
+def another_func():
+ for _ in range(3):
+ try:
+ continue
+ finally:
+ print("Finally!")
+
+def one_more_func():
+ try:
+ for i in range(3):
+ try:
+ 1 / i
+ except ZeroDivisionError:
+ # بذارید اینجا ارور بدیم و بیرون حلقه بهش
+ # رسیدگی کنیم
+ raise ZeroDivisionError("A trivial divide by zero error")
+ finally:
+ print("Iteration", i)
+ break
+ except ZeroDivisionError as e:
+ print("Zero division error occurred", e)
+```
+
+**خروجی:**
+
+```py
+>>> some_func()
+'from_finally'
+
+>>> another_func()
+Finally!
+Finally!
+Finally!
+
+>>> 1 / 0
+Traceback (most recent call last):
+ File "", line 1, in
+ZeroDivisionError: division by zero
+
+>>> one_more_func()
+Iteration 0
+
+```
+
+#### 💡 توضیح:
+
+- وقتی یک عبارت `return`، `break` یا `continue` داخل بخش `try` از یک عبارت "try...finally" اجرا میشه، بخش `fianlly` هم هنگام خارج شدن اجرا میشه.
+- مقدار بازگشتی یک تابع از طریق آخرین عبارت `return` که داخل تابع اجرا میشه، مشخص میشه. از اونجایی که بخش `finally` همیشه اجرا میشه، عبارت `return` که داخل بخش `finally` هست آخرین عبارتیه که اجرا میشه.
+- نکته اینجاست که اگه بخش داخل بخش `finally` یک عبارت `return` یا `break` اجرا بشه، `exception` موقتی که ذخیره شده، رها میشه.
+
+---
+
+### ◀ برای چی؟
+
+
+
+```py
+some_string = "wtf"
+some_dict = {}
+for i, some_dict[i] in enumerate(some_string):
+ i = 10
+```
+
+**خروجی:**
+
+```py
+>>> some_dict # یک دیکشنری مرتبشده نمایان میشه.
+{0: 'w', 1: 't', 2: 'f'}
+```
+
+#### 💡 توضیح:
+
+- یک حلقه `for` در [گرامر پایتون](https://docs.python.org/3/reference/grammar.html) این طور تعریف میشه:
+
+ ```bash
+ for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite]
+ ```
+
+ به طوری که `exprlist` یک هدف برای مقداردهیه. این یعنی، معادل عبارت `{exprlist} = {next_value}` **برای هر شیء داخل `testlist` اجرا میشود**.
+ یک مثال جالب برای نشون دادن این تعریف:
+
+ ```py
+ for i in range(4):
+ print(i)
+ i = 10
+ ```
+
+ **خروجی:**
+
+ ```bash
+ 0
+ 1
+ 2
+ 3
+ ```
+
+ آیا انتظار داشتید که حلقه فقط یک بار اجرا بشه؟
+
+ **💡 توضیح:**
+
+ - عبارت مقداردهی `i = 10` به خاطر نحوه کار کردن حلقهها، هیچوقت باعث تغییر در تکرار حلقه نمیشه. قبل از شروع هر تکرار، مقدار بعدی که توسط شیء قابل تکرار (که در اینجا `range(4)` است) ارائه میشه، از بسته خارج میشه و به متغیرهای لیست هدف (که در اینجا `i` است) مقداردهی میشه.
+
+- تابع `enumerate(some_string)`، یک متغیر `i` (که یک شمارنده افزایشی است) و یک حرف از حروف رشته `some_string` رو در هر تکرار برمیگردونه. و بعدش برای کلید `i` (تازه مقداردهیشده) در دیکشنری `some_dict`، مقدار اون حرف رو تنظیم میکنه. بازشده این حلقه میتونه مانند مثال زیر ساده بشه:
+
+ ```py
+ >>> i, some_dict[i] = (0, 'w')
+ >>> i, some_dict[i] = (1, 't')
+ >>> i, some_dict[i] = (2, 'f')
+ >>> some_dict
+ ```
+
+---
+
+### ◀ اختلاف زمانی در محاسبه
+
+
+
+1\.
+
+```py
+array = [1, 8, 15]
+# یک عبارت تولیدکننده عادی
+gen = (x for x in array if array.count(x) > 0)
+array = [2, 8, 22]
+```
+
+**خروجی:**
+
+```py
+>>> print(list(gen)) # پس بقیه مقدارها کجا رفتن؟
+[8]
+```
+
+2\.
+
+```py
+array_1 = [1,2,3,4]
+gen_1 = (x for x in array_1)
+array_1 = [1,2,3,4,5]
+
+array_2 = [1,2,3,4]
+gen_2 = (x for x in array_2)
+array_2[:] = [1,2,3,4,5]
+```
+
+**خروجی:**
+
+```py
+>>> print(list(gen_1))
+[1, 2, 3, 4]
+
+>>> print(list(gen_2))
+[1, 2, 3, 4, 5]
+```
+
+3\.
+
+```py
+array_3 = [1, 2, 3]
+array_4 = [10, 20, 30]
+gen = (i + j for i in array_3 for j in array_4)
+
+array_3 = [4, 5, 6]
+array_4 = [400, 500, 600]
+```
+
+**خروجی:**
+
+```py
+>>> print(list(gen))
+[401, 501, 601, 402, 502, 602, 403, 503, 603]
+```
+
+#### 💡 توضیح
+
+- در یک عبارت [تولیدکننده](https://wiki.python.org/moin/Generators)، عبارت بند `in` در هنگام تعریف محاسبه میشه ولی عبارت شرطی در زمان اجرا محاسبه میشه.
+- پس قبل از زمان اجرا، `array` دوباره با لیست `[2, 8, 22]` مقداردهی میشه و از آنجایی که در مقدار جدید `array`، بین `1`، `8` و `15`، فقط تعداد `8` بزرگتر از `0` است، تولیدکننده فقط مقدار `8` رو برمیگردونه
+- تفاوت در مقدار `gen_1` و `gen_2` در بخش دوم به خاطر نحوه مقداردهی دوباره `array_1` و `array_2` است.
+- در مورد اول، متغیر `array_1` به شیء جدید `[1,2,3,4,5]` وصله و از اون جایی که عبارت بند `in` در هنگام تعریف محاسبه میشه، `array_1` داخل تولیدکننده هنوز به شیء قدیمی `[1,2,3,4]` (که هنوز حذف نشده)
+- در مورد دوم، مقداردهی برشی به `array_2` باعث بهروز شدن شیء قدیمی این متغیر از `[1,2,3,4]` به `[1,2,3,4,5]` میشه و هر دو متغیر `gen_2` و `array_2` به یک شیء اشاره میکنند که حالا بهروز شده.
+- خیلیخب، حالا طبق منطقی که تا الان گفتیم، نباید مقدار `list(gen)` در قطعهکد سوم، `[11, 21, 31, 12, 22, 32, 13, 23, 33]` باشه؟ (چون `array_3` و `array_4` قراره درست مثل `array_1` رفتار کنن). دلیل این که چرا (فقط) مقادیر `array_4` بهروز شدن، توی [PEP-289](https://www.python.org/dev/peps/pep-0289/#the-details) توضیح داده شده.
+
+ > فقط بیرونیترین عبارت حلقه `for` بلافاصله محاسبه میشه و باقی عبارتها به تعویق انداخته میشن تا زمانی که تولیدکننده اجرا بشه.
+
+---
+
+### ◀ هر گردی، گردو نیست
+
+
+
+```py
+>>> 'something' is not None
+True
+>>> 'something' is (not None)
+False
+```
+
+#### 💡 توضیح
+
+- عملگر `is not` یک عملگر باینری واحده و رفتارش متفاوت تر از استفاده `is` و `not` به صورت جداگانهست.
+- عملگر `is not` مقدار `False` رو برمیگردونه اگر متغیرها در هردو سمت این عملگر به شیء یکسانی اشاره کنند و درغیر این صورت، مقدار `True` برمیگردونه
+- در مثال بالا، عبارت `(not None)` برابره با مقدار `True` از اونجایی که مقدار `None` در زمینه boolean به `False` تبدیل میشه. پس کل عبارت معادل عبارت `'something' is True` میشه.
+
+---
+
+### ◀ یک بازی دوز که توش X همون اول برنده میشه!
+
+
+
+```py
+
+# بیاید یک سطر تشکیل بدیم
+
+row = [""] * 3 #row i['', '', '']
+
+# حالا بیاید تخته بازی رو ایجاد کنیم
+
+board = [row] * 3
+
+```
+
+**خروجی:**
+
+```py
+>>> board
+[['', '', ''], ['', '', ''], ['', '', '']]
+>>> board[0]
+['', '', '']
+>>> board[0][0]
+''
+>>> board[0][0] = "X"
+>>> board
+[['X', '', ''], ['X', '', ''], ['X', '', '']]
+```
+
+ما که سهتا `"X"` نذاشتیم. گذاشتیم مگه؟
+
+#### 💡 توضیح:
+
+وقتی متغیر `row` رو تشکیل میدیم، تصویر زیر نشون میده که چه اتفاقی در حافظه دستگاه میافته.
+
+
+
+
+
+
+
+
+
+و وقتی متغیر `board` رو با ضرب کردن متغیر `row` تشکیل میدیم، تصویر زیر به صورت کلی نشون میده که چه اتفاقی در حافظه میافته (هر کدوم از عناصر `board[0]`، `board[1]` و `board[2]` در حافظه به لیست یکسانی به نشانی `row` اشاره میکنند).
+
+
Изучение и понимание Python с помощью удивительных примеров поведения.
Переводы: [English Original](https://github.com/satwikkansal/wtfpython) [Chinese 中文](https://github.com/robertparley/wtfpython-cn) | [Vietnamese Tiếng Việt](https://github.com/vuduclyunitn/wtfptyhon-vi) | [Spanish Español](https://web.archive.org/web/20220511161045/https://github.com/JoseDeFreitas/wtfpython-es) | [Korean 한국어](https://github.com/buttercrab/wtfpython-ko) | [Russian Русский](https://github.com/satwikkansal/wtfpython/tree/master/translations/ru-russian) | [German Deutsch](https://github.com/BenSt099/wtfpython) | [Add translation](https://github.com/satwikkansal/wtfpython/issues/new?title=Add%20translation%20for%20[LANGUAGE]&body=Expected%20time%20to%20finish:%20[X]%20weeks.%20I%27ll%20start%20working%20on%20it%20from%20[Y].)
-Альтернативные способы: [Интерактивный сайт](https://wtfpython-interactive.vercel.app) | [Интерактивный Jupiter notebook](https://colab.research.google.com/github/satwikkansal/wtfpython/blob/master/irrelevant/wtf.ipynb) | [CLI](https://pypi.python.org/pypi/wtfpython)
+Альтернативные способы: [Интерактивный сайт](https://wtfpython-interactive.vercel.app) | [Интерактивный Jupiter notebook](https://colab.research.google.com/github/satwikkansal/wtfpython/blob/master/irrelevant/wtf.ipynb)
Python, будучи прекрасно спроектированным высокоуровневым языком программирования, предоставляет множество возможностей для удобства программиста. Но иногда поведение Python кода могут показаться запутывающим на первый взгляд.
@@ -209,13 +215,6 @@ PS: Если вы уже читали **wtfpython** раньше, с измен
- Если ответ отрицательный (что совершенно нормально), сделать глубокий вдох и прочитать объяснение (а если пример все еще непонятен, и создайте [issue](https://github.com/satwikkansal/wtfpython/issues/new)).
- Если "да", ощутите мощь своих познаний в Python и переходите к следующему примеру.
-PS: Вы также можете читать WTFPython в командной строке, используя [pypi package](https://pypi.python.org/pypi/wtfpython),
-
-```sh
-pip install wtfpython -U
-wtfpython
-```
-
# 👀 Примеры
## Раздел: Напряги мозги!
@@ -408,7 +407,13 @@ False
- Все строки длиной 0 или 1 символа интернируются.
- Строки интернируются во время компиляции (`'wtf'` будет интернирована, но `''.join(['w'', 't', 'f'])` - нет)
- Строки, не состоящие из букв ASCII, цифр или знаков подчеркивания, не интернируются. В примере выше `'wtf!'` не интернируется из-за `!`. Реализацию этого правила в CPython можно найти [здесь](https://github.com/python/cpython/blob/3.6/Objects/codeobject.c#L19)
- 
+
+
+
+
+
+
+
- Когда переменные `a` и `b` принимают значение `"wtf!"` в одной строке, интерпретатор Python создает новый объект, а затем одновременно ссылается на вторую переменную. Если это выполняется в отдельных строках, он не "знает", что уже существует `"wtf!"` как объект (потому что `"wtf!"` не является неявно интернированным в соответствии с фактами, упомянутыми выше). Это оптимизация во время компиляции, не применяется к версиям CPython 3.7.x (более подробное обсуждение смотрите [здесь](https://github.com/satwikkansal/wtfpython/issues/100)).
- Единица компиляции в интерактивной среде IPython состоит из одного оператора, тогда как в случае модулей она состоит из всего модуля. `a, b = "wtf!", "wtf!"` - это одно утверждение, тогда как `a = "wtf!"; b = "wtf!"` - это два утверждения в одной строке. Это объясняет, почему тождества различны в `a = "wtf!"; b = "wtf!"`, но одинаковы при вызове в модуле.
- Резкое изменение в выводе четвертого фрагмента связано с [peephole optimization](https://en.wikipedia.org/wiki/Peephole_optimization) техникой, известной как складывание констант (англ. Constant folding). Это означает, что выражение `'a'*20` заменяется на `'aaaaaaaaaaaaaaaaaaaa'` во время компиляции, чтобы сэкономить несколько тактов во время выполнения. Складывание констант происходит только для строк длиной менее 21. (Почему? Представьте себе размер файла `.pyc`, созданного в результате выполнения выражения `'a'*10**10`). [Вот](https://github.com/python/cpython/blob/3.6/Python/peephole.c#L288) исходный текст реализации для этого.
@@ -554,7 +559,7 @@ False
Интерпретатор не понимает, что до выполнения выражения `y = 257` целое число со значением `257` уже создано, и поэтому он продолжает создавать другой объект в памяти.
-Подобная оптимизация применима и к другим **изменяемым** объектам, таким как пустые кортежи. Поскольку списки являются изменяемыми, поэтому `[] is []` вернет `False`, а `() is ()` вернет `True`. Это объясняет наш второй фрагмент. Перейдем к третьему,
+Подобная оптимизация применима и к другим **неизменяемым** объектам, таким как пустые кортежи. Поскольку списки являются изменяемыми, поэтому `[] is []` вернет `False`, а `() is ()` вернет `True`. Это объясняет наш второй фрагмент. Перейдем к третьему,
**И `a`, и `b` ссылаются на один и тот же объект при инициализации одним и тем же значением в одной и той же строке**.
@@ -1038,11 +1043,23 @@ board = [row] * 3
Когда мы инициализируем переменную `row`, эта визуализация объясняет, что происходит в памяти
-
+
+
+
+
+
+
+
А когда переменная `board` инициализируется путем умножения `row`, вот что происходит в памяти (каждый из элементов `board[0]`, `board[1]` и `board[2]` является ссылкой на тот же список, на который ссылается `row`)
-
+
+
+
+
+
+
+
Мы можем избежать этого сценария, не используя переменную `row` для генерации `board`. (Подробнее в [issue](https://github.com/satwikkansal/wtfpython/issues/68)).
diff --git a/wtfpython-pypi/content.md b/wtfpython-pypi/content.md
deleted file mode 100644
index 0d246693..00000000
--- a/wtfpython-pypi/content.md
+++ /dev/null
@@ -1,2386 +0,0 @@
-
-
What the f*ck Python! 🐍
-
An interesting collection of surprising snippets and lesser-known Python features.
+ 
+ 
+ 
+ ![\"\"](\"/images/logo.png\"){kind=logo}
![\"wtfpython](\"https://raw.githubusercontent.com/satwikkansal/wtfpython/refs/heads/master/images/logo.svg\"){kind=logo}
\n",
"![\"Shows](\"https://raw.githubusercontent.com/satwikkansal/wtfpython/refs/heads/master/images/string-intern/string_interning.svg\")
\n",
"+ When `a` and `b` are set to `\"wtf!\"` in the same line, the Python interpreter creates a new object, then references the second variable at the same time. If you do it on separate lines, it doesn't \"know\" that there's already `\"wtf!\"` as an object (because `\"wtf!\"` is not implicitly interned as per the facts mentioned above). It's a compile-time optimization. This optimization doesn't apply to 3.7.x versions of CPython (check this [issue](https://github.com/satwikkansal/wtfpython/issues/100) for more discussion).\n",
"+ A compile unit in an interactive environment like IPython consists of a single statement, whereas it consists of the entire module in case of modules. `a, b = \"wtf!\", \"wtf!\"` is single statement, whereas `a = \"wtf!\"; b = \"wtf!\"` are two statements in a single line. This explains why the identities are different in `a = \"wtf!\"; b = \"wtf!\"`, and also explain why they are same when invoked in `some_file.py`\n",
"+ The abrupt change in the output of the fourth snippet is due to a [peephole optimization](https://en.wikipedia.org/wiki/Peephole_optimization) technique known as Constant folding. This means the expression `'a'*20` is replaced by `'aaaaaaaaaaaaaaaaaaaa'` during compilation to save a few clock cycles during runtime. Constant folding only occurs for strings having a length of less than 21. (Why? Imagine the size of `.pyc` file generated as a result of the expression `'a'*10**10`). [Here's](https://github.com/python/cpython/blob/3.6/Python/peephole.c#L288) the implementation source for the same.\n",
@@ -2947,11 +2938,11 @@
"\n",
"When we initialize `row` variable, this visualization explains what happens in the memory\n",
"\n",
- "\n",
+ "![\"Shows](\"https://raw.githubusercontent.com/satwikkansal/wtfpython/refs/heads/master/images/tic-tac-toe/after_row_initialized.svg\")
\n",
"\n",
"And when the `board` is initialized by multiplying the `row`, this is what happens inside the memory (each of the elements `board[0]`, `board[1]` and `board[2]` is a reference to the same list referred by `row`)\n",
"\n",
- "\n",
+ "![\"Shows](\"https://raw.githubusercontent.com/satwikkansal/wtfpython/refs/heads/master/images/tic-tac-toe/after_board_initialized.svg\")
\n",
"\n",
"We can avoid this scenario here by not using `row` variable to generate `board`. (Asked in [this](https://github.com/satwikkansal/wtfpython/issues/68) issue).\n",
"\n"
@@ -13475,4 +13466,4 @@
"metadata": {},
"nbformat": 4,
"nbformat_minor": 2
-}
\ No newline at end of file
+}
diff --git a/noxfile.py b/noxfile.py
new file mode 100644
index 00000000..f693b854
--- /dev/null
+++ b/noxfile.py
@@ -0,0 +1,13 @@
+from typing import TYPE_CHECKING
+
+import nox
+
+
+if TYPE_CHECKING:
+ from nox.sessions import Session
+
+python_versions = ["3.9", "3.10", "3.11", "3.12", "3.13"]
+
+@nox.session(python=python_versions, reuse_venv=True)
+def tests(session: "Session") -> None:
+ _ = session.run("python", "snippets/2_tricky_strings.py")
diff --git a/poetry.lock b/poetry.lock
new file mode 100644
index 00000000..47b34986
--- /dev/null
+++ b/poetry.lock
@@ -0,0 +1,155 @@
+# This file is automatically @generated by Poetry 1.8.3 and should not be changed by hand.
+
+[[package]]
+name = "argcomplete"
+version = "3.5.1"
+description = "Bash tab completion for argparse"
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "argcomplete-3.5.1-py3-none-any.whl", hash = "sha256:1a1d148bdaa3e3b93454900163403df41448a248af01b6e849edc5ac08e6c363"},
+ {file = "argcomplete-3.5.1.tar.gz", hash = "sha256:eb1ee355aa2557bd3d0145de7b06b2a45b0ce461e1e7813f5d066039ab4177b4"},
+]
+
+[package.extras]
+test = ["coverage", "mypy", "pexpect", "ruff", "wheel"]
+
+[[package]]
+name = "colorama"
+version = "0.4.6"
+description = "Cross-platform colored terminal text."
+optional = false
+python-versions = "!=3.0.*,!=3.1.*,!=3.2.*,!=3.3.*,!=3.4.*,!=3.5.*,!=3.6.*,>=2.7"
+files = [
+ {file = "colorama-0.4.6-py2.py3-none-any.whl", hash = "sha256:4f1d9991f5acc0ca119f9d443620b77f9d6b33703e51011c16baf57afb285fc6"},
+ {file = "colorama-0.4.6.tar.gz", hash = "sha256:08695f5cb7ed6e0531a20572697297273c47b8cae5a63ffc6d6ed5c201be6e44"},
+]
+
+[[package]]
+name = "colorlog"
+version = "6.8.2"
+description = "Add colours to the output of Python's logging module."
+optional = false
+python-versions = ">=3.6"
+files = [
+ {file = "colorlog-6.8.2-py3-none-any.whl", hash = "sha256:4dcbb62368e2800cb3c5abd348da7e53f6c362dda502ec27c560b2e58a66bd33"},
+ {file = "colorlog-6.8.2.tar.gz", hash = "sha256:3e3e079a41feb5a1b64f978b5ea4f46040a94f11f0e8bbb8261e3dbbeca64d44"},
+]
+
+[package.dependencies]
+colorama = {version = "*", markers = "sys_platform == \"win32\""}
+
+[package.extras]
+development = ["black", "flake8", "mypy", "pytest", "types-colorama"]
+
+[[package]]
+name = "distlib"
+version = "0.3.9"
+description = "Distribution utilities"
+optional = false
+python-versions = "*"
+files = [
+ {file = "distlib-0.3.9-py2.py3-none-any.whl", hash = "sha256:47f8c22fd27c27e25a65601af709b38e4f0a45ea4fc2e710f65755fa8caaaf87"},
+ {file = "distlib-0.3.9.tar.gz", hash = "sha256:a60f20dea646b8a33f3e7772f74dc0b2d0772d2837ee1342a00645c81edf9403"},
+]
+
+[[package]]
+name = "filelock"
+version = "3.16.1"
+description = "A platform independent file lock."
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "filelock-3.16.1-py3-none-any.whl", hash = "sha256:2082e5703d51fbf98ea75855d9d5527e33d8ff23099bec374a134febee6946b0"},
+ {file = "filelock-3.16.1.tar.gz", hash = "sha256:c249fbfcd5db47e5e2d6d62198e565475ee65e4831e2561c8e313fa7eb961435"},
+]
+
+[package.extras]
+docs = ["furo (>=2024.8.6)", "sphinx (>=8.0.2)", "sphinx-autodoc-typehints (>=2.4.1)"]
+testing = ["covdefaults (>=2.3)", "coverage (>=7.6.1)", "diff-cover (>=9.2)", "pytest (>=8.3.3)", "pytest-asyncio (>=0.24)", "pytest-cov (>=5)", "pytest-mock (>=3.14)", "pytest-timeout (>=2.3.1)", "virtualenv (>=20.26.4)"]
+typing = ["typing-extensions (>=4.12.2)"]
+
+[[package]]
+name = "nox"
+version = "2024.10.9"
+description = "Flexible test automation."
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "nox-2024.10.9-py3-none-any.whl", hash = "sha256:1d36f309a0a2a853e9bccb76bbef6bb118ba92fa92674d15604ca99adeb29eab"},
+ {file = "nox-2024.10.9.tar.gz", hash = "sha256:7aa9dc8d1c27e9f45ab046ffd1c3b2c4f7c91755304769df231308849ebded95"},
+]
+
+[package.dependencies]
+argcomplete = ">=1.9.4,<4"
+colorlog = ">=2.6.1,<7"
+packaging = ">=20.9"
+tomli = {version = ">=1", markers = "python_version < \"3.11\""}
+virtualenv = ">=20.14.1"
+
+[package.extras]
+tox-to-nox = ["jinja2", "tox"]
+uv = ["uv (>=0.1.6)"]
+
+[[package]]
+name = "packaging"
+version = "24.1"
+description = "Core utilities for Python packages"
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "packaging-24.1-py3-none-any.whl", hash = "sha256:5b8f2217dbdbd2f7f384c41c628544e6d52f2d0f53c6d0c3ea61aa5d1d7ff124"},
+ {file = "packaging-24.1.tar.gz", hash = "sha256:026ed72c8ed3fcce5bf8950572258698927fd1dbda10a5e981cdf0ac37f4f002"},
+]
+
+[[package]]
+name = "platformdirs"
+version = "4.3.6"
+description = "A small Python package for determining appropriate platform-specific dirs, e.g. a `user data dir`."
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "platformdirs-4.3.6-py3-none-any.whl", hash = "sha256:73e575e1408ab8103900836b97580d5307456908a03e92031bab39e4554cc3fb"},
+ {file = "platformdirs-4.3.6.tar.gz", hash = "sha256:357fb2acbc885b0419afd3ce3ed34564c13c9b95c89360cd9563f73aa5e2b907"},
+]
+
+[package.extras]
+docs = ["furo (>=2024.8.6)", "proselint (>=0.14)", "sphinx (>=8.0.2)", "sphinx-autodoc-typehints (>=2.4)"]
+test = ["appdirs (==1.4.4)", "covdefaults (>=2.3)", "pytest (>=8.3.2)", "pytest-cov (>=5)", "pytest-mock (>=3.14)"]
+type = ["mypy (>=1.11.2)"]
+
+[[package]]
+name = "tomli"
+version = "2.0.2"
+description = "A lil' TOML parser"
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "tomli-2.0.2-py3-none-any.whl", hash = "sha256:2ebe24485c53d303f690b0ec092806a085f07af5a5aa1464f3931eec36caaa38"},
+ {file = "tomli-2.0.2.tar.gz", hash = "sha256:d46d457a85337051c36524bc5349dd91b1877838e2979ac5ced3e710ed8a60ed"},
+]
+
+[[package]]
+name = "virtualenv"
+version = "20.27.0"
+description = "Virtual Python Environment builder"
+optional = false
+python-versions = ">=3.8"
+files = [
+ {file = "virtualenv-20.27.0-py3-none-any.whl", hash = "sha256:44a72c29cceb0ee08f300b314848c86e57bf8d1f13107a5e671fb9274138d655"},
+ {file = "virtualenv-20.27.0.tar.gz", hash = "sha256:2ca56a68ed615b8fe4326d11a0dca5dfbe8fd68510fb6c6349163bed3c15f2b2"},
+]
+
+[package.dependencies]
+distlib = ">=0.3.7,<1"
+filelock = ">=3.12.2,<4"
+platformdirs = ">=3.9.1,<5"
+
+[package.extras]
+docs = ["furo (>=2023.7.26)", "proselint (>=0.13)", "sphinx (>=7.1.2,!=7.3)", "sphinx-argparse (>=0.4)", "sphinxcontrib-towncrier (>=0.2.1a0)", "towncrier (>=23.6)"]
+test = ["covdefaults (>=2.3)", "coverage (>=7.2.7)", "coverage-enable-subprocess (>=1)", "flaky (>=3.7)", "packaging (>=23.1)", "pytest (>=7.4)", "pytest-env (>=0.8.2)", "pytest-freezer (>=0.4.8)", "pytest-mock (>=3.11.1)", "pytest-randomly (>=3.12)", "pytest-timeout (>=2.1)", "setuptools (>=68)", "time-machine (>=2.10)"]
+
+[metadata]
+lock-version = "2.0"
+python-versions = "^3.9"
+content-hash = "af91619c8e62e649ee538e51a248ef2fc1e4f4495e7748b3b551685aa47b404e"
diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 00000000..a048fafe
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,16 @@
+[tool.poetry]
+name = "wtfpython"
+version = "3.0.0"
+description = "What the f*ck Python!"
+authors = ["Satwik Kansal 
-+ When `a` and `b` are set to `"wtf!"` in the same line, the Python interpreter creates a new object, then references the second variable at the same time. If you do it on separate lines, it doesn't "know" that there's already `wtf!` as an object (because `"wtf!"` is not implicitly interned as per the facts mentioned above). It's a compiler optimization and specifically applies to the interactive environment.
-+ Constant folding is a technique for [peephole optimization](https://en.wikipedia.org/wiki/Peephole_optimization) in Python. This means the expression `'a'*20` is replaced by `'aaaaaaaaaaaaaaaaaaaa'` during compilation to reduce few clock cycles during runtime. Constant folding only occurs for strings having length less than 20. (Why? Imagine the size of `.pyc` file generated as a result of the expression `'a'*10**10`). [Here's](https://github.com/python/cpython/blob/3.6/Python/peephole.c#L288) the implementation source for the same.
-
-
----
-
-### ▶ Time for some hash brownies!
-
-1\.
-```py
-some_dict = {}
-some_dict[5.5] = "Ruby"
-some_dict[5.0] = "JavaScript"
-some_dict[5] = "Python"
-```
-
-**Output:**
-```py
->>> some_dict[5.5]
-"Ruby"
->>> some_dict[5.0]
-"Python"
->>> some_dict[5]
-"Python"
-```
-
-"Python" destroyed the existence of "JavaScript"?
-
-#### 💡 Explanation
-
-* Python dictionaries check for equality and compare the hash value to determine if two keys are the same.
-* Immutable objects with same value always have the same hash in Python.
- ```py
- >>> 5 == 5.0
- True
- >>> hash(5) == hash(5.0)
- True
- ```
- **Note:** Objects with different values may also have same hash (known as hash collision).
-* When the statement `some_dict[5] = "Python"` is executed, the existing value "JavaScript" is overwritten with "Python" because Python recognizes `5` and `5.0` as the same keys of the dictionary `some_dict`.
-* This StackOverflow [answer](https://stackoverflow.com/a/32211042/4354153) explains beautifully the rationale behind it.
-
----
-
-### ▶ Return return everywhere!
-
-```py
-def some_func():
- try:
- return 'from_try'
- finally:
- return 'from_finally'
-```
-
-**Output:**
-```py
->>> some_func()
-'from_finally'
-```
-
-#### 💡 Explanation:
-
-- When a `return`, `break` or `continue` statement is executed in the `try` suite of a "try…finally" statement, the `finally` clause is also executed ‘on the way out.
-- The return value of a function is determined by the last `return` statement executed. Since the `finally` clause always executes, a `return` statement executed in the `finally` clause will always be the last one executed.
-
----
-
-### ▶ Deep down, we're all the same. *
-
-```py
-class WTF:
- pass
-```
-
-**Output:**
-```py
->>> WTF() == WTF() # two different instances can't be equal
-False
->>> WTF() is WTF() # identities are also different
-False
->>> hash(WTF()) == hash(WTF()) # hashes _should_ be different as well
-True
->>> id(WTF()) == id(WTF())
-True
-```
-
-#### 💡 Explanation:
-
-* When `id` was called, Python created a `WTF` class object and passed it to the `id` function. The `id` function takes its `id` (its memory location), and throws away the object. The object is destroyed.
-* When we do this twice in succession, Python allocates the same memory location to this second object as well. Since (in CPython) `id` uses the memory location as the object id, the id of the two objects is the same.
-* So, object's id is unique only for the lifetime of the object. After the object is destroyed, or before it is created, something else can have the same id.
-* But why did the `is` operator evaluated to `False`? Let's see with this snippet.
- ```py
- class WTF(object):
- def __init__(self): print("I")
- def __del__(self): print("D")
- ```
-
- **Output:**
- ```py
- >>> WTF() is WTF()
- I
- I
- D
- D
- False
- >>> id(WTF()) == id(WTF())
- I
- D
- I
- D
- True
- ```
- As you may observe, the order in which the objects are destroyed is what made all the difference here.
-
----
-
-### ▶ For what?
-
-```py
-some_string = "wtf"
-some_dict = {}
-for i, some_dict[i] in enumerate(some_string):
- pass
-```
-
-**Output:**
-```py
->>> some_dict # An indexed dict is created.
-{0: 'w', 1: 't', 2: 'f'}
-```
-
-#### 💡 Explanation:
-
-* A `for` statement is defined in the [Python grammar](https://docs.python.org/3/reference/grammar.html) as:
- ```
- for_stmt: 'for' exprlist 'in' testlist ':' suite ['else' ':' suite]
- ```
- Where `exprlist` is the assignment target. This means that the equivalent of `{exprlist} = {next_value}` is **executed for each item** in the iterable.
- An interesting example that illustrates this:
- ```py
- for i in range(4):
- print(i)
- i = 10
- ```
-
- **Output:**
- ```
- 0
- 1
- 2
- 3
- ```
-
- Did you expect the loop to run just once?
-
- **💡 Explanation:**
-
- - The assignment statement `i = 10` never affects the iterations of the loop because of the way for loops work in Python. Before the beginning of every iteration, the next item provided by the iterator (`range(4)` this case) is unpacked and assigned the target list variables (`i` in this case).
-
-* The `enumerate(some_string)` function yields a new value `i` (A counter going up) and a character from the `some_string` in each iteration. It then sets the (just assigned) `i` key of the dictionary `some_dict` to that character. The unrolling of the loop can be simplified as:
- ```py
- >>> i, some_dict[i] = (0, 'w')
- >>> i, some_dict[i] = (1, 't')
- >>> i, some_dict[i] = (2, 'f')
- >>> some_dict
- ```
-
----
-
-### ▶ Evaluation time discrepancy
-
-1\.
-```py
-array = [1, 8, 15]
-g = (x for x in array if array.count(x) > 0)
-array = [2, 8, 22]
-```
-
-**Output:**
-```py
->>> print(list(g))
-[8]
-```
-
-2\.
-
-```py
-array_1 = [1,2,3,4]
-g1 = (x for x in array_1)
-array_1 = [1,2,3,4,5]
-
-array_2 = [1,2,3,4]
-g2 = (x for x in array_2)
-array_2[:] = [1,2,3,4,5]
-```
-
-**Output:**
-```py
->>> print(list(g1))
-[1,2,3,4]
-
->>> print(list(g2))
-[1,2,3,4,5]
-```
-
-#### 💡 Explanation
-
-- In a [generator](https://wiki.python.org/moin/Generators) expression, the `in` clause is evaluated at declaration time, but the conditional clause is evaluated at runtime.
-- So before runtime, `array` is re-assigned to the list `[2, 8, 22]`, and since out of `1`, `8` and `15`, only the count of `8` is greater than `0`, the generator only yields `8`.
-- The differences in the output of `g1` and `g2` in the second part is due the way variables `array_1` and `array_2` are re-assigned values.
-- In the first case, `array_1` is binded to the new object `[1,2,3,4,5]` and since the `in` clause is evaluated at the declaration time it still refers to the old object `[1,2,3,4]` (which is not destroyed).
-- In the second case, the slice assignment to `array_2` updates the same old object `[1,2,3,4]` to `[1,2,3,4,5]`. Hence both the `g2` and `array_2` still have reference to the same object (which has now been updated to `[1,2,3,4,5]`).
-
----
-
-### ▶ `is` is not what it is!
-
-The following is a very famous example present all over the internet.
-
-```py
->>> a = 256
->>> b = 256
->>> a is b
-True
-
->>> a = 257
->>> b = 257
->>> a is b
-False
-
->>> a = 257; b = 257
->>> a is b
-True
-```
-
-#### 💡 Explanation:
-
-**The difference between `is` and `==`**
-
-* `is` operator checks if both the operands refer to the same object (i.e., it checks if the identity of the operands matches or not).
-* `==` operator compares the values of both the operands and checks if they are the same.
-* So `is` is for reference equality and `==` is for value equality. An example to clear things up,
- ```py
- >>> [] == []
- True
- >>> [] is [] # These are two empty lists at two different memory locations.
- False
- ```
-
-**`256` is an existing object but `257` isn't**
-
-When you start up python the numbers from `-5` to `256` will be allocated. These numbers are used a lot, so it makes sense just to have them ready.
-
-Quoting from https://docs.python.org/3/c-api/long.html
-> The current implementation keeps an array of integer objects for all integers between -5 and 256, when you create an int in that range you just get back a reference to the existing object. So it should be possible to change the value of 1. I suspect the behavior of Python, in this case, is undefined. :-)
-
-```py
->>> id(256)
-10922528
->>> a = 256
->>> b = 256
->>> id(a)
-10922528
->>> id(b)
-10922528
->>> id(257)
-140084850247312
->>> x = 257
->>> y = 257
->>> id(x)
-140084850247440
->>> id(y)
-140084850247344
-```
-
-Here the interpreter isn't smart enough while executing `y = 257` to recognize that we've already created an integer of the value `257,` and so it goes on to create another object in the memory.
-
-**Both `a` and `b` refer to the same object when initialized with same value in the same line.**
-
-```py
->>> a, b = 257, 257
->>> id(a)
-140640774013296
->>> id(b)
-140640774013296
->>> a = 257
->>> b = 257
->>> id(a)
-140640774013392
->>> id(b)
-140640774013488
-```
-
-* When a and b are set to `257` in the same line, the Python interpreter creates a new object, then references the second variable at the same time. If you do it on separate lines, it doesn't "know" that there's already `257` as an object.
-* It's a compiler optimization and specifically applies to the interactive environment. When you enter two lines in a live interpreter, they're compiled separately, therefore optimized separately. If you were to try this example in a `.py` file, you would not see the same behavior, because the file is compiled all at once.
-
----
-
-### ▶ A tic-tac-toe where X wins in the first attempt!
-
-```py
-# Let's initialize a row
-row = [""]*3 #row i['', '', '']
-# Let's make a board
-board = [row]*3
-```
-
-**Output:**
-```py
->>> board
-[['', '', ''], ['', '', ''], ['', '', '']]
->>> board[0]
-['', '', '']
->>> board[0][0]
-''
->>> board[0][0] = "X"
->>> board
-[['X', '', ''], ['X', '', ''], ['X', '', '']]
-```
-
-We didn't assign 3 "X"s or did we?
-
-#### 💡 Explanation:
-
-When we initialize `row` variable, this visualization explains what happens in the memory
-
-
-
-And when the `board` is initialized by multiplying the `row`, this is what happens inside the memory (each of the elements `board[0]`, `board[1]` and `board[2]` is a reference to the same list referred by `row`)
-
-
-
-We can avoid this scenario here by not using `row` variable to generate `board`. (Asked in [this](https://github.com/satwikkansal/wtfpython/issues/68) issue).
-
-```py
->>> board = [['']*3 for _ in range(3)]
->>> board[0][0] = "X"
->>> board
-[['X', '', ''], ['', '', ''], ['', '', '']]
-```
-
----
-
-### ▶ The sticky output function
-
-```py
-funcs = []
-results = []
-for x in range(7):
- def some_func():
- return x
- funcs.append(some_func)
- results.append(some_func()) # note the function call here
-
-funcs_results = [func() for func in funcs]
-```
-
-**Output:**
-```py
->>> results
-[0, 1, 2, 3, 4, 5, 6]
->>> funcs_results
-[6, 6, 6, 6, 6, 6, 6]
-```
-Even when the values of `x` were different in every iteration prior to appending `some_func` to `funcs`, all the functions return 6.
-
-//OR
-
-```py
->>> powers_of_x = [lambda x: x**i for i in range(10)]
->>> [f(2) for f in powers_of_x]
-[512, 512, 512, 512, 512, 512, 512, 512, 512, 512]
-```
-
-#### 💡 Explanation
-
-- When defining a function inside a loop that uses the loop variable in its body, the loop function's closure is bound to the variable, not its value. So all of the functions use the latest value assigned to the variable for computation.
-
-- To get the desired behavior you can pass in the loop variable as a named variable to the function. **Why this works?** Because this will define the variable again within the function's scope.
-
- ```py
- funcs = []
- for x in range(7):
- def some_func(x=x):
- return x
- funcs.append(some_func)
- ```
-
- **Output:**
- ```py
- >>> funcs_results = [func() for func in funcs]
- >>> funcs_results
- [0, 1, 2, 3, 4, 5, 6]
- ```
-
----
-
-### ▶ `is not ...` is not `is (not ...)`
-
-```py
->>> 'something' is not None
-True
->>> 'something' is (not None)
-False
-```
-
-#### 💡 Explanation
-
-- `is not` is a single binary operator, and has behavior different than using `is` and `not` separated.
-- `is not` evaluates to `False` if the variables on either side of the operator point to the same object and `True` otherwise.
-
----
-
-### ▶ The surprising comma
-
-**Output:**
-```py
->>> def f(x, y,):
-... print(x, y)
-...
->>> def g(x=4, y=5,):
-... print(x, y)
-...
->>> def h(x, **kwargs,):
- File "