On Tue, Apr 21, 2020 at 11:36 AM Serhiy Storchaka <storch...@gmail.com> wrote:
> 20.04.20 23:33, Andrew Barnert via Python-ideas пише: > > Should this print 1 or 2 or raise StopIteration or be a don’t-care? > > > > Should it matter if you zip(y, x, strict=True) instead? > > It should print 2 in both cases. The only way to determine whether the > iterator ends is to try to get its next value. And this value (1) will > lost, because there is no way to return it or "unput" to the iterator. > There is no reason to consume more values, so StopIteration is irrelevant. > > There is more interesting example: > > x = iter(range(5)) > y = [0] > z = iter(range(5)) > try: > zipped = list(zip(x, y, z, strict=True)) > except ValueError: # assuming that’s the exception you want? > assert zipped == [(0, 0, 0)] > assert next(x) == 2 > print(next(z)) > > Should this print 1 or 2? > > The simple implementation using zip_longest() would print 2, but more > optimal implementation can print 1. > Your first assert is wrong. I think it should print 1 (i.e. raise the exception immediately when the first iterator is too short) but I don't feel too strongly about this, so if people are pushing towards 2, I'm okay with that. If there's agreement to move forward on this suggestion, here's what I volunteer to do: 1. Write tests. 2. Write documentation. I'm gonna need someone else to write the implementation.
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