On Monday, September 3, 2012 3:28:28 PM UTC-5, Dave Angel wrote: > On 09/03/2012 04:04 PM, Aaron Brady wrote: > > > On Monday, September 3, 2012 2:30:24 PM UTC-5, Ian wrote: > > >> On Sun, Sep 2, 2012 at 11:43 AM, Aaron Brady <castiro...@gmail.com> wrote: > > >> > > >>> We could use a Python long object for the version index to prevent > >>> overflow. Combined with P. Rubin's idea to count the number of open > >>> iterators, most use cases still wouldn't exceed a single word comparison; > >>> we could reset the counter when there weren't any. > > >> > > >> > > >> We could use a Python long; I just don't think the extra overhead is > > >> > > >> justified in a data structure that is already highly optimized for > > >> > > >> speed. Incrementing and testing a C int is *much* faster than doing > > >> > > >> the same with a Python long. > > > I think the technique would require two python longs and a bool in the set, > > and a python long in the iterator. > > > > > > One long counts the number of existing (open) iterators. Another counts > > the version. The bool keeps track of whether an iterator has been created > > since the last modification, in which case the next modification requires > > incrementing the version and resetting the flag. > > > > I think you're over-engineering the problem. it's a bug if an iterator > > is used after some change is made to the set it's iterating over. We > > don't need to catch every possible instance of the bug, that's what > > testing is for. The point is to "probably" detect it, and for that, all > > we need is a counter in the set and a counter in the open iterator. > > Whenever changing the set, increment its count. And whenever iterating, > > check the two counters. if they don't agree, throw an exception, and > > destroy the iterator. i suppose that could be done with a flag, but it > > could just as easily be done by zeroing the pointer to the set. > > > > I'd figure a byte or two would be good enough for the counts, but a C > > uint would be somewhat faster, and wouldn't wrap as quickly. > > > > -- > > > > DaveA
Hi D. Angel, The serial index constantly reminds me of upper limits. I have the same problem with PHP arrays, though it's not a problem with the language itself. The linked list doesn't have a counter, it invalidates iterators when a modification is made, therefore it's the "correct" structure in my interpretation. But it does seem more precarious comparatively, IMHO. Both strategies solve the problem I posed originally, they both involve trade-offs, and it's too late to include either in 3.3.0. -- http://mail.python.org/mailman/listinfo/python-list
