Is it safe to modify elements inside an enumerate() loop if it is followed by a break?

Question

I've written some python code which loops through a list like below:

for idx, r in enumerate(mylist):
    if condition:
        del mylist[idx]
        break

My question is, whether it is safe to modify this list inside the loop (like in the above example) as long as I have that break statement? Or should I still be modifying the list outside of the loop?

Answer 1

Yes it is safe if this code is not concurrent if other threads are not going to use mylist concurrently. But as long as we have GIL I think it safe to do it. Better way is to wrap it in a function and return a new copy this way it will be side effects free

def create_my_list(mylist):
  mylist = mylist[:] #to create local copy as mylist is passed by reference
  #mylist is a localcopy here
  for idx, r in enumerate(mylist):
      if condition:
        del mylist[idx]
        break
  return mylist