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Python Python Collections (2016, retired 2019) Lists Removing items from a list

Posted by thomas2017
thomas2017
1,342 Points

Python Collections: Removing Items from a List Challenge Task 2

messy_list = ["a", 2, 3, 1, False, [1, 2, 3]]

# Your code goes below here
messy_list.insert(0, messy_list.pop(3))

for x in messy_list.copy():
    if isinstance(x, (bool, str, list)):
        messy_list.remove(x)

Hello, can someone please tell me why this isn't working. In another post on the forum about this page that states that I shouldn't mess with the list directly as it cause the order of the index to get mess up. So I did it with a copy of the list but that didn't seem to fix it.

3 Answers

Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

List objects don't have a "copy" method. Perhaps you're thinking of dictionaries.

But you can make a copy using a slice with no parameters. If you do that instead, your code should pass the challenge:

for x in messy_list[:]:
Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

Odd, I did find "copy" listed in the documentation. But when I tried it in my Python, I got "AttributeError: 'list' object has no attribute 'copy'". Maybe I just have a old version and this is something new.

thomas2017
thomas2017
1,342 Points
thomas2017
thomas2017
1,342 Points

I'm not sure if if it does or not.

I just saw someone else post the answer.

https://teamtreehouse.com/community/python-collections-removing-items-from-a-list-challenge-task-2-2

-Answered by Chris Freeman "Using your third code attempt, It can pass the challenge if you make a copy of messy_list for the for loop. This way, the deletions do not alter the indexes of the copy."

messy_list = ["a", 2, 3, 1, False, [1, 2, 3]]

# Your code goes below here
messy_list.insert(0, messy_list.pop(3))
for item in messy_list.copy():  # <-- iterate over a copy of messy_list
    if type(item) != int:
        print(item)
        del messy_list[messy_list.index(item)]
Steven Parker
Steven Parker
231,269 Points
Steven Parker
Steven Parker
231,269 Points

That code also seems to be trying to use a "copy" method on a list. I would not expect that to work, either.

But I added a suggestion to my original answer.

Bob Pickles
Bob Pickles
1,363 Points
Bob Pickles
Bob Pickles
1,363 Points

I didn't think about copying it. I'm gonna to back and try it. I ended up doing it with a list comprehension (although it doesn't use remove, it just creates a new list with only the ints)

Adding here for completeness: messy_list = [x for x in messy_list if type(x) is int

Also, from what I understand (and i'd like an actual python dev to chime in on this). According to the pep8 standard, you should use is not instead of != against singletons like "None" (which i assume in this case int is)