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Python

Posted by john larson
john larson
16,594 Points

How would I pass a False Boolean when doing pop on a list

It keeps stopping at the False. I tried pass, continue, I even tried if item == False: False = True. 

lst = [1,2,3, False, 4,5,6]
for l in lst:
    if l == False:  
        # pass or continue did not work
    else:
        item = lst.pop()
        print(item)
john larson
john larson
16,594 Points

Hi Alex, I just wanted to pop the whole list (skipping over false) and print it. I came across something like this, there's supposed to be a way to do it but I can't find anything on it and the stuff I tried doesn't work.

3 Answers

Steven Parker
Steven Parker
243,318 Points
Steven Parker
Steven Parker
243,318 Points

You are depleting your list as you loop through it.

You are using the list itself to control the loop:

for l in lst:

But, while looping, you are removing items from the list:

        item = lst.pop()

So when you reduce the size of the list to the number of times the loop has already run, it will stop.

If I understand what you're intending, you probably need to control your loop another way, perhaps using the initial length of the list. Then, you should pop your item first and examine it directly. Something like this:

for i in range(len(lst)):
    item = lst.pop()
    if item == False:  
        continue
    else:
        print(item)

Isn't that what you were after?

john larson
john larson
16,594 Points

Thanks Steve.

Alexander Davison
Alexander Davison
65,469 Points
Alexander Davison
Alexander Davison
65,469 Points

If you are attempting to remove the False value from the list, you can use the built-in remove function.

Example:

my_list = ["a", 3, 5, 9, 2, False, [1, 2, 3, False]]
my_list.remove(False)
print(my_list)

This will output:

["a", 3, 5, 9, 2, [1, 2, 3, False]]

I hope this helps. ~Alex

Alexander Davison
Alexander Davison
65,469 Points
Alexander Davison
Alexander Davison
65,469 Points

To remove all items but one value (not element), you can do this:

my_list = ["a", 3, 5, 9, 2, False, [1, 2, 3, False], False]

for item in my_list:
    if item != False:
        my_list.remove(item)

I hope this helps. ~Alex

john larson
john larson
16,594 Points

Thanks Alex, that gives me some ideas. There was this challenge on codewars about moving all the 0's to the end of the list. There was a False in the list. I finally figured out that False stops the iteration if pop() is used on the list.

Steven Parker
Steven Parker
243,318 Points
Steven Parker
Steven Parker
243,318 Points

It's not the popped value that stops the iteration, it's the depletion of the list. This example also suffers from list depletion. It looks like it should finish with my_list containing "[False, False]".

But what my_list actually contains at the end is: "[3, 9, False, False]" because for each element that is removed, another one escapes notice in the iteration.