Remove not int elements in list

Question

Hi I have this task in python and I should remove all not int elements, the result of the code down below is [2, 3, 1, [1, 2, 3]] and I have no idea why in the result the list is not moved away. Only tested suggestions please, I mean working ones.

# Great! Now use .remove() and/or del to remove the string, 
# the boolean, and the list from inside of messy_list. 
# When you're done, messy_list should have only integers in it
messy_list = ["a", 2, 3, 1, False, [1, 2, 3]]
for ele in messy_list:  
   print('the type of {} is  {} '.format(ele,type(ele)))
   if type(ele) is not int:
     messy_list.remove(ele)
     print(messy_list)

You're modifying the list while iterating over it. That behaviour is undefined. In particular, in this case, it seems that it removes `False`, therefore moving the list into `False`'s old position, and then finds that the next index is out of bounds for the list. You should create a new list, or really, use a list comprehension. — Mees de Vries, Apr 30 '18 at 15:33
@MeesdeVries The behaviour is defined and consistent, it's just not intuitive so not recommended — Chris_Rands, Apr 30 '18 at 15:40

Austin · Answer 1 · 2018-04-30T15:49:29.120

3

Try this one:

>>> messy_list = ["a", 2, 3, 1, False, [1, 2, 3]]
>>> [elem for elem in messy_list if type(elem) == int]
[2, 3, 1]

edited Apr 30 '18 at 15:49

answered Apr 30 '18 at 15:41

Austin

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3

`type(1)` is just `int` – Chris_Rands Apr 30 '18 at 15:44
@Chris_Rands isn't that OP wants? Title says - Remove not int elements from list – Austin Apr 30 '18 at 15:45
I think `if type(elem) is int` might be better in this case – TwistedSim Apr 30 '18 at 15:47
2

Yes but why would you call `type(1)` every time, when you know the type is `int`? just use `type(elem) == int` – Chris_Rands Apr 30 '18 at 15:48

score 2 · Answer 2 · answered Apr 30 '18 at 15:47

The issue is not related to the presence of a list inside your messy_list, but rather to the fact you are modifying the list while iterating over it.

For example, with messy_list = ["a", 2, 3, 1, False, "a"] you would get [2, 3, 1, "a"] as a result.

On the other hand: [elem for elem in messy_list if type(elem) == int] returns [2, 3, 1], which is what you want.

Remove not int elements in list

2 Answers2