set and dict iteration

[88888 Dihedral]

Paul Rubin於 2012年8月17日星期五UTC+8上午9時01分39秒寫道：
> 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.

If there is only one iterator of a frozen dictionary,
then nothing is saved.

But if there are manny iterators based on the same frozen dictionary, 
this approach saves a lot.