Why wouldn't this code work?

Question

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?

Answer 1 · 2015-02-01T11:25:41Z

February 1, 2015 11:25am

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])

Welcome to the Treehouse Community

Looking to learn something new?

Akshat Jain

Akshat Jain

Why wouldn't this code work?

1 Answer

William Li

William Li

Akshat Jain

Akshat Jain