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Python Python Collections (Retired) Lists Redux Pop

Posted by Venkiteswaran Subramanian
Venkiteswaran Subramanian
7,643 Points

Only odd indexed items in the list getting deleted while trying to clear the entire list using remove method

I am trying to clear all the items in a list using remove() function using the below code. But, only the odd numbered items are getting removed from the list

code:

def clear_items(): for item in shopping_list: shopping_list.remove(item)

Thomas Kirk
Thomas Kirk
5,246 Points
Thomas Kirk
Thomas Kirk
5,246 Points

As I understand it, your for loop is removing an item from each index point.

It removes the item at shopping_list[0], then the item at shopping_list[1],...

The problem with this is, as items are removed, the index of the remaining items change. When [0] is removed, [1] becomes [0], and [2] becomes [1] etc, so items are skipped in the loop.

4 Answers

Kenneth Love
STAFF
Kenneth Love
Treehouse Guest Teacher
Kenneth Love
Kenneth Love
Treehouse Guest Teacher

Don't modify the length of a list while you're working through it. If you need to zero out the list for some reason, either set it to a new, blank list:

my_list = []

Or use the .clear() method.

my_list.clear()
Geroge Harris
Geroge Harris
1,279 Points
Geroge Harris
Geroge Harris
1,279 Points

tried below and it worked (put a while loop before the for iteration)

def clear_items(list_to_clear): while len(list_to_clear)>0: for item in list_to_clear: list_to_clear.remove(item)

clear_items(shopping_list)

you could also just use shopping_list =0 if you don't have to use remove.

Venkiteswaran Subramanian
Venkiteswaran Subramanian
7,643 Points
Venkiteswaran Subramanian
Venkiteswaran Subramanian
7,643 Points

Thanks everyone! Answers were really helpful.

David Sudermann
PLUS
David Sudermann
Courses Plus Student 3,228 Points
David Sudermann
David Sudermann
Courses Plus Student 3,228 Points

It's an old question, but since I ran into the very same problem, here my solution:

def clear_items(a_list):
  for item in a_list[:]:
    a_list.remove(item)

This way the list that is being iterated over is not changing and skipping issues are prevented.

For clearing purposes setting the list to an empty list, like Kenneth suggested, is more efficient. I used it to remove non-integer items:

def remove_nonint(a_list):
  for item in a_list[:]:
    if type(item) != int:
      a_list.remove(item)