[Python-ideas] Re: Invalidate list iterators after size changes?

On 9/10/21 11:24 am, Tyler Hou via Python-ideas wrote:

Right now, the following code is valid in Python 3.9 (and infinitely loops):

``` lst = [1, 2, 3] for i in lst: lst.append(i) ```

1. If the size of a list, set, or dict changes, invalidate all existing iterators to that containers.

This would break Plex. I use a loop like that as part of the NFA-to-DFA conversion to calculate the epsilon-closure of a state (although obviously there are conditions on adding things to the list that ensure it terminates). -- Greg