set and dict iteration

[Paul Rubin]

Ian Kelly <ian.g.kelly at gmail.com> writes:
> With regard to key insertion and deletion while iterating over a dict
> or set, though, there is just no good reason to be doing that
> (especially as the result is very implementation-specific), and I
> wouldn't mind a more complete low-level check against it as long as
> it's not too expensive (which is not clearly the case with the current
> suggestion at all).

One possible approach is to freeze the dictionary against modification
while any iterator is open on it.  You could keep a count of active
iterators in the dict structure, adjusting it whenever an iterator is
created or closed/destroyed.