Re: [pygame] Iterate over list and delete

[Ian Mallett <ian@xxxxxxxxxxxxxx>]

On Sun, May 20, 2018 at 8:35 PM, Daniel Foerster <pydsigner@xxxxxxxxx> wrote:

The third, and probably most convenient based on where you seem to be at in the curriculum, is to do something like Ian suggested. I think there's a simpler way to do it with similar performance though I've not benched to find out; I don't think autoresizing should be too much of a concern, especially early in a class like this.

index = 0

# Could also use a for loop to avoid repeatedly len()ing:

## for _discarded in range(len(my_list)):

while index < len(my_list):
    if need_to_delete(my_list[index]):
        del my_list[index]
        # We don't need to update the index after deleting because now the next
        # item is sitting in the current slot
    else:
        index += 1

​The `list` type is an array, so the `del` operation is implicitly copying the remaining elements of the list forward. This will be O(n^2) operations over the whole algorithm. My example copies each element at most once, so there are only O(n) operations total. This version may be more clear, though.

Ian​