List index out of range in loop

Question

Im getting an error for list index being out of range. Sorry if this is a stupid question.

def filter_list(l):
  for x in range(0, len(l)):
     if type(l[x]) is str:
       del l[x]
  return l

Though you would get away with it if you looped in the reverse direction `range(len(l) - 1, -1, -1)` — alani, Jul 04 '20 at 06:50

Khoi-Viet Le · Accepted Answer · 2020-07-04T06:56:47.267

0

When you use del to delete the item in the list, the list actually shortens and it seems like that is what is causing the problem.

If you would like to filter lists, you could use list comprehensions like so:

def filter(l):
    return [item for item in l if type(item) is not str]

Usually, when looping over lists, it is good practice not to delete or insert new items.

Hope this helped

edited Jul 04 '20 at 06:56

answered Jul 04 '20 at 06:52

Khoi-Viet Le

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Or just use the builtin `filter` function – rdas Jul 04 '20 at 06:53
It's bad practice to overload built-in function names. – Nick Jul 04 '20 at 06:56

score 0 · Answer 2 · answered Jul 04 '20 at 06:56

You should not definitely change a list while iterating over it. It is very bad practise... it can lead to a whole lot of errors for you. Either you should create a copy of use something else, as list comprehension:

def filter_list(l):
    return [x for x in l if type(x) is not str]

print(filter_list([1, 4, 5, 's', 'demo'])) # Prints [1, 4, 5]

List index out of range in loop

2 Answers2