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Python Python Collections (Retired) Lists Redux Manipulating Lists

Posted by Akshat Jain
Akshat Jain
6,810 Points

Why wouldn't this code work?

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

for item in the_list: if type(item) is str or type(item) is bool or type(item) is list: the_list.remove(item)

The last item(the list) still remains. I don't understand, what am I doing wrong?

1 Answer

William Li
PLUS
William Li
Courses Plus Student 26,868 Points
William Li
William Li
Courses Plus Student 26,868 Points

Akshat Jain Hi, You can't just iterate though a list while removing item from it, because it change the length of the list. well, technically Python won't stop you from doing that, but the result won't be what your expected.

In your for loop, when it runs, it will assign each element in the_list to item and execute the loop body for each.

In the first run of for loop, the first item in the_list "a" was assigned to item, but in the loop body, you remove it from the_list; so in the next run of your loop, the 2nd item in the new list [2, 3, 1, False, [1, 2, 3]], which is 3, got assigned to item. You see the problem here? 2 was never checked due to the length change of the the_list. You should be able to see why your end result included unwanted item.

I think for this code challenge, it only ask you to manually remove the item from the list one by one using .remove() and/or del. So I suggest you just hand code it, and don't try anything too fancy.

the_list.remove("a")
the_list.remove(False)
the_list.remove([1,2,3])
Akshat Jain
Akshat Jain
6,810 Points

Thanks! That solved my doubt