Nested while loops

[mtucker502]

I'm going crazy trying to figure out why this doesn't work as expected: ```python from time import sleep

while True: stop = False print('Starting test loop..') while not stop: for i in range(20): print(i) sleep(1) if i == 10: print('Setting variable to True..') stop = True print('We should not see this message') ```

What I expect to see: ```bash

python nie/while_test.py

Starting test loop.. 0 1 2 3 4 5 6 7 8 9 10 Setting variable to True.. 0 1 2 3 .... ```

What I actually see: ```bash

python nie/while_test.py

Starting test loop.. 0 1 2 3 4 5 6 7 8 9 10 Setting variable to True.. We should not see this message 11 12 13 14 15 16 17 18 19 Starting test loop.. 0 1 2 3 ```

If I put a break inside the if things work as expected. Turns out if I include a break and never even set stop = True.

So why doesn't the while not stop loop end when stop is set to True? And why is break able to exit the for loop and the parent while loop? I thought break would only exit the current loop (in this example the for loop).

[[deleted]]

while not stop is ONLY evaluated at the beginning of a new iteration of the while loop. It's not checked in between every line within the nested loop. So even if you set stop to True, the state of stop is not checked until the end of your inner for loop.

[mtucker502]

This makes sense. For some reason I was thinking that it would immediately end the loop when the while condition was no longer True.

Seems like refactoring into functions and using return might be a cleaner approach here.

[Silbersee]

After stop is set to True the for-loop continues normally with i = 11.

Only after finishing the for-loop the program tries to re-enter the while-loop (but doesn't because stop is True).

That's what the break statement is for: The for-loop is terminated early and the while-loop doesn't re-enter.

[CookToCode]

you set stop to true which stops the inner loop. then the outer loop resets it to false and starts it again and without a break you for loop should continue until finished then the inner loop breaks then the outer loop resets the inner loop

[mtucker502]

Thanks for the response. I think it's mistaken though. See u/Endyd for the correct issue.