deleting select items from a list

[Yoriz]

Modifying a list (or other container) while iterating over it

for laser in lasers:
    ...
    if rm:
        lasers.remove(laser)

This will cause an IndexError when you iterate over the loop as you have just removed an index from the list that you are looping over. A catch 22. You need to loop the list in order to remove, but you cannot remove from the list as you loop. This can be easily fixed by looping a copy of the list and removing from the actual list. All you have to do to loop a copy is add [:].

for laser in lasers[:]:
    ...
    if rm:
        lasers.remove(laser)

The [:] is a shallow copy. The is identical to using the copy module for copy.copy(). If you have nested structures you may want a deep copy. This you are going to need to use copy.deepcopy() See more info here