On Wed, Oct 19, 2016 at 1:33 PM, Yury Selivanov <yselivanov...@gmail.com> wrote: > On 2016-10-19 3:33 PM, Nathaniel Smith wrote: > >>>>>>> lst = [1,2,3,4] >>>>>>> >>>>>it = iter(lst) >>>>>>> >>>>>for i in it: >>>> >>>> >>... if i == 2: break >>>> >> >>>>>>> >>>>>>> >>>>>for i in it: >>>> >>>> >>... print(i) >>>> >>3 >>>> >>4 >>>>>>> >>>>>>> >>>>> >>>> >>>> >> >>>> >>With the proposed behaviour, if I understand it, "it" would be closed >>>> >>after the first loop, so resuming "it" for the second loop wouldn't >>>> >>work. Am I right in that? I know there's a proposed itertools function >>>> >>to bring back the old behaviour, but it's still a compatibility break. >>>> >>And code like this, that partially consumes an iterator, is not >>>> >>uncommon. >>> >>> > >>> >Right -- did you reach the "transition plan" section? (I know it's >>> >wayyy down there.) The proposal is to hide this behind a __future__ at >>> >first + a mechanism during the transition period to catch code that >>> >depends on the old behavior and issue deprecation warnings. But it is >>> >a compatibility break, yes. >> >> I should also say, regarding your specific example, I guess it's an >> open question whether we would want list_iterator.__iterclose__ to >> actually do anything. It could flip the iterator to a state where it >> always raises StopIteration, or RuntimeError, or it could just be a >> no-op that allows iteration to continue normally afterwards. > > > Making 'for' loop to behave differently for built-in containers (i.e. make > __iterclose__ a no-op for them) will only make this whole thing even more > confusing. > > It has to be consistent: if you partially iterate over *anything* without > wrapping it with `preserve()`, it should always close the iterator.
You're probably right. My gut is leaning the same way, I'm just hesitant to commit because I haven't thought about it for long. But I do stand by the claim that this is probably not *that* important either way :-). -n -- Nathaniel J. Smith -- https://vorpus.org _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
