Is this behavior of list iteration guaranteed by documentation
anywhere? A quick search didn't yield any results for me.

If not, I suggest either:

a) it gets documented so developers can rely on it, or
b) the lack of guarantee is documented so that we can reserve a change
of behavior later.

Paul


On Sun, 2021-10-10 at 13:17 +1300, Greg Ewing wrote:
> 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).
> 

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