How to remove even numbers from a list in Python? [duplicate]

Question

I'm trying to remove even numbers from a list. My final output is [4,8] but it is supposed to be empty.

list = [2, 4, 6, 8, 10]
for i in list:
    divid = i %2
    if divid == 0 :
        list.remove(i)
print(list)

Answer 1

You are modifying the list as you iterate over it. Imagine a pointer moving along the list. For the first iteration, the index is 0 (and i is 2). You remove the first value and return to the start of the loop.

The index is incremented (to 1) and i is now the second value in the list (now 6) which is also removed. Notice that 4 is now 'behind' the index of the iterator and will never be reached. Continuing along the list you will remove every second value leaving [4, 8].

A couple of pointers. To loop over a list like this you can use for i in list[:]: which copies the list before iterating over it. Also avoid naming variables things like list which override builtin types. You'll cause bugs later in your code.

Answer 2

As others have pointed out, you should not modify a list and iterate over it at the same time. The simplest solution is to create a new list with the required modifications:

lst = [2, 4, 6, 8, 10]
new_lst = [i for i in lst if i % 2 != 0]

The above uses a list comprehension to create a new list with only the odd elements - which is the same as removing the even elements from the original list.