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Decorator, Duck types, Enum, Exceptions
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‎README.md

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@@ -640,9 +640,9 @@ import zoneinfo, dateutil.tz
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### Decode
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```python
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<str> = <D/T/DT>.isoformat(sep='T') # Also `timespec='auto/hours/minutes/seconds/…'`.
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<str> = <D/T/DT>.isoformat(sep='T') # Also `timespec='auto/hours/minutes/seconds…'`.
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<str> = <D/T/DT>.strftime('<format>') # Custom string representation of the object.
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<int> = <D/DT>.toordinal() # Days since NYE 1, ignoring time and timezone.
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<int> = <D/DT>.toordinal() # Days since NYE 1. Ignores DT's time and zone.
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<float> = <DTn>.timestamp() # Seconds since the Epoch, from local naive DT.
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<float> = <DTa>.timestamp() # Seconds since the Epoch, from aware datetime.
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```
@@ -794,7 +794,7 @@ from functools import reduce
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### Walrus Operator
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```python
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>>> [i for a in '0123' if (i := int(a)) > 0] # Assigns to variable mid-sentence.
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>>> [i for ch in '0123' if (i := int(ch)) > 0] # Assigns to variable mid-sentence.
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[1, 2, 3]
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```
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@@ -885,8 +885,7 @@ def get_counter():
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Decorator
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---------
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* **A decorator takes a function, adds some functionality and returns it.**
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* **It can be any [callable](#callable), but is usually implemented as a function that returns a [closure](#closure).**
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**A decorator takes a function, adds some functionality and returns it. It can be any [callable](#callable), but is usually implemented as a function that returns a [closure](#closure).**
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```python
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@decorator_name
@@ -1094,7 +1093,7 @@ Duck Types
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**A duck type is an implicit type that prescribes a set of special methods. Any object that has those methods defined is considered a member of that duck type.**
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### Comparable
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* **If eq() method is not overridden, it returns `'id(self) == id(other)'`, which is the same as `'self is other'`. That means all user-defined objects compare not equal by default, because id() returns object's unique identification number (its memory address).**
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* **If eq() method is not overridden, it returns `'id(self) == id(other)'`, which is the same as `'self is other'`. That means all user-defined objects compare not equal by default (because id() returns object's memory address that is unique during its lifetime).**
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* **Only the left side object has eq() method called, unless it returns NotImplemented, in which case the right object is consulted. False is returned if both return NotImplemented.**
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* **Ne() automatically works on any object that has eq() defined.**
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@@ -1199,8 +1198,8 @@ class Counter:
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### Context Manager
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* **With statements only work on objects that have enter() and exit() special methods.**
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* **Enter() should lock the resources and optionally return an object.**
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* **Exit() should release the resources (for example close a file).**
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* **Enter() should lock the resources and optionally return an object (file, lock, etc.).**
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* **Exit() should release the resources (for example close a file, release a lock, etc.).**
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* **Any exception that happens inside the with block is passed to the exit() method.**
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* **The exit() method can suppress the exception by returning a true value.**
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```python
@@ -1332,8 +1331,8 @@ from enum import Enum, auto
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```python
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class <enum_name>(Enum):
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<member_name> = auto() # Increment of the last numeric value or 1.
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<member_name> = <value> # Values don't have to be hashable.
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<member_name> = <el_1>, <el_2> # Values can be collections (this is a tuple).
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<member_name> = <value> # Values don't have to be hashable or unique.
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<member_name> = <el_1>, <el_2> # Values can be collections, like this tuple.
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```
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* **Methods receive the member they were called on as the 'self' argument.**
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* **Accessing a member named after a reserved keyword causes SyntaxError.**
@@ -1342,20 +1341,20 @@ class <enum_name>(Enum):
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<member> = <enum>.<member_name> # Returns a member. Raises AttributeError.
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<member> = <enum>['<member_name>'] # Returns a member. Raises KeyError.
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<member> = <enum>(<value>) # Returns a member. Raises ValueError.
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<str> = <member>.name # Returns member's name.
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<obj> = <member>.value # Returns member's value.
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<str> = <member>.name # Returns the member's name.
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<obj> = <member>.value # Returns the member's value.
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```
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```python
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<list> = list(<enum>) # Returns enum's members.
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<list> = [a.name for a in <enum>] # Returns enum's member names.
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<list> = [a.value for a in <enum>] # Returns enum's member values.
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<list> = list(<enum>) # Returns a list of enum's members.
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<list> = <enum>._member_names_ # Returns a list of member names.
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<list> = [m.value for m in <enum>] # Returns a list of member values.
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```
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```python
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<enum> = type(<member>) # Returns member's enum.
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<iter> = itertools.cycle(<enum>) # Returns endless iterator of members.
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<member> = random.choice(list(<enum>)) # Returns a random member.
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<enum> = type(<member>) # Returns an enum. Also <memb>.__class__.
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<iter> = itertools.cycle(<enum>) # Returns an endless iterator of members.
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<member> = random.choice(list(<enum>)) # Randomly selects one of the members.
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```
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### Inline
@@ -1397,8 +1396,8 @@ finally:
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```
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* **Code inside the `'else'` block will only be executed if `'try'` block had no exceptions.**
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* **Code inside the `'finally'` block will always be executed (unless a signal is received).**
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* **All variables that are initialized in executed blocks are also visible in all subsequent blocks, as well as outside the try statement (only function block delimits scope).**
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* **To catch signals use `'signal.signal(signal_number, <func>)'`.**
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* **All variables that are initialized in executed blocks are also visible in all subsequent blocks, as well as outside the try statement (only a function block delimits scope).**
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* **To catch signals use `'signal.signal(signal_number, handler_function)'`.**
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### Catching Exceptions
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```python
@@ -1407,10 +1406,10 @@ except <exception> as <name>: ...
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except (<exception>, [...]): ...
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except (<exception>, [...]) as <name>: ...
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```
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* **Also catches subclasses of the exception.**
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* **Use `'traceback.print_exc()'` to print the full error message to stderr.**
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* **Use `'print(<name>)'` to print just the cause of the exception (its arguments).**
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* **Use `'logging.exception(<str>)'` to log the passed message, followed by the full error message of the caught exception. For details see [Logging](#logging).**
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* **Also catches subclasses, e.g. `'IndexError'` is caught by `'except LookupError:'`.**
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* **Use `'traceback.print_exc()'` to print the full error message to standard error stream.**
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* **Use `'print(<name>)'` to print just the cause of the exception (i.e. its arguments).**
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* **Use `'logging.exception(<str>)'` to log the passed message, followed by the full error message of the caught exception. For details about setting up the logger see [Logging](#logging).**
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* **Use `'sys.exc_info()'` to get exception type, object, and traceback of caught exception.**
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### Raising Exceptions
@@ -1433,33 +1432,33 @@ arguments = <name>.args
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exc_type = <name>.__class__
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filename = <name>.__traceback__.tb_frame.f_code.co_filename
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func_name = <name>.__traceback__.tb_frame.f_code.co_name
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line = linecache.getline(filename, <name>.__traceback__.tb_lineno)
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line_str = linecache.getline(filename, <name>.__traceback__.tb_lineno)
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trace_str = ''.join(traceback.format_tb(<name>.__traceback__))
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error_msg = ''.join(traceback.format_exception(type(<name>), <name>, <name>.__traceback__))
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```
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### Built-in Exceptions
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```text
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BaseException
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+-- SystemExit # Raised by the sys.exit() function.
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+-- KeyboardInterrupt # Raised when the user hits the interrupt key (ctrl-c).
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+-- SystemExit # Raised by the sys.exit() function (see #Exit for details).
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+-- KeyboardInterrupt # Raised when the user hits the interrupt key (control-c).
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+-- Exception # User-defined exceptions should be derived from this class.
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+-- ArithmeticError # Base class for arithmetic errors such as ZeroDivisionError.
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+-- AssertionError # Raised by `assert <exp>` if expression returns false value.
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+-- AttributeError # Raised when object doesn't have requested attribute/method.
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+-- EOFError # Raised by input() when it hits an end-of-file condition.
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+-- LookupError # Base class for errors when a collection can't find an item.
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| +-- IndexError # Raised when a sequence index is out of range.
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| +-- IndexError # Raised when index of a sequence (list/str) is out of range.
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| +-- KeyError # Raised when a dictionary key or set element is missing.
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+-- MemoryError # Out of memory. May be too late to start deleting variables.
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+-- NameError # Raised when nonexistent name (variable/func/class) is used.
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| +-- UnboundLocalError # Raised when local name is used before it's being defined.
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+-- OSError # Errors such as FileExistsError/TimeoutError (see #Open).
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| +-- ConnectionError # Errors such as BrokenPipeError/ConnectionAbortedError.
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+-- OSError # Errors such as FileExistsError, TimeoutError (see #Open).
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| +-- ConnectionError # Errors such as BrokenPipeError and ConnectionAbortedError.
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+-- RuntimeError # Raised by errors that don't fall into other categories.
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| +-- NotImplementedEr… # Can be raised by abstract methods or by unfinished code.
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| +-- RecursionError # Raised if max recursion depth is exceeded (3k by default).
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+-- StopIteration # Raised when an empty iterator is passed to next().
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+-- StopIteration # Raised when exhausted (empty) iterator is passed to next().
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+-- TypeError # When an argument of the wrong type is passed to function.
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+-- ValueError # When argument has the right type but inappropriate value.
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```

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