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‎if.md

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@@ -73,6 +73,19 @@ but it's not possible to create custom keywords. That's why keywords are
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usually used for "magic" things that would be difficult to do with just
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functions.
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Also note that if statements check the condition once only, so if you
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set it to false later the if statement won't notice it.
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```py
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>>> its_raining = True
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>>> if its_raining:
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... its_raining = False
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... print("It's not raining, but this runs anyway.")
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...
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It's not raining, but this runs anyway.
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>>>
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```
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## Storing code in files
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At this point it's easier to put your code into a file and use it
@@ -167,7 +180,20 @@ else:
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print("It's not raining.")
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```
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By combining that with the input function we can make a program that
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The else part simply runs when the if statement doesn't run. It doesn't
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check the condition again.
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```py
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>>> its_raining = True
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>>> if its_raining:
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... its_raining = False
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... else:
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... print("It's not raining, but this still doesn't run.")
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...
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>>>
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```
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By combining `else` with the input function we can make a program that
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asks for a password and checks if it's correct.
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```py

‎loops.md

Lines changed: 37 additions & 7 deletions
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@@ -84,6 +84,19 @@ Running the program may look like this:
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Or is it? (y=yes, n=no) n
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It's not raining anymore.
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The while loop doesn't check the condition all the time, it only checks
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it in the beginning.
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```py
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>>> its_raining = True
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>>> while its_raining:
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... its_raining = False
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... print("It's not raining, but the while loop doesn't know it yet.")
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...
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It's not raining, but the while loop doesn't know it yet.
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>>>
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```
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We can also interrupt a loop even if the condition is still true using
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the `break` keyword. In this case, we'll set condition to True and rely
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on nothing but `break` to end the loop.
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Is it raining? (y=yes, n=no) n
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It's not raining anymore.
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Unlike setting the condition to False, breaking the loop ends it
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immediately.
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```py
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>>> while True:
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... break
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... print("This is never printed.")
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...
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>>>
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```
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## Until loops
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Python doesn't have until loops. If you need an until loop, use
@@ -154,7 +178,7 @@ We could also create an index variable, and use a while loop:
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```py
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>>> stuff = ['hello', 'hi', 'how are you doing', 'im fine', 'how about you']
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>>> length_of_stuff = len(stuff) # len(x) is the length of x, 5 in this case
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>>> length_of_stuff = len(stuff) # len(stuff) is 5
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>>> index = 0
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>>> while index < length_of_stuff:
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... print(stuff[index])
@@ -168,8 +192,9 @@ how about you
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>>>
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```
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But there's `len()` and an index variable we need to increment. That's
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a lot of stuff to worry about for just printing each item.
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But there's `len()` and an index variable we need to increment and a
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while loop and many other things to worry about. That's a lot of work
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just for printing each item.
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This is when for loops come in:
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@@ -202,8 +227,12 @@ how about you
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>>>
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```
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There's only one big limitation with for looping over lists. You
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shouldn't modify the list in the for loop. If you do, the results can
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Right now the while loop version might seem easier to understand for
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you, but later you'll realize that for loops are much easier to work
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with than while loops and index variables, especially in large projects.
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There's only one big limitation with for looping over lists. We
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shouldn't modify the list in the for loop. If we do, the results can
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be surprising:
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```py
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>>>
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```
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Instead, you can create a copy of stuff and loop over it.
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Instead, we can create a copy of stuff and loop over it.
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```py
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>>> stuff = ['hello', 'hi', 'how are you doing', 'im fine', 'how about you']
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>>>
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```
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Or if you want to clear a list, just use the `.clear()` list method:
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Or if we just want to clear a list, we can use the `clear`
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[list method](https://docs.python.org/3/tutorial/datastructures.html#more-on-lists):
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```py
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>>> stuff = ['hello', 'hi', 'how are you doing', 'im fine', 'how about you']

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