On Thu, Sep 2, 2021 at 7:43 PM Yury Selivanov <yselivanov...@gmail.com> wrote:
> Comments inlined: > > On Thu, Sep 2, 2021 at 6:23 PM Guido van Rossum <gu...@python.org> wrote: > >> First of all, we should ping Yury, who implemented `async for` about 6 >> years ago (see PEP 492), and Joshua Bronson, who implemented aiter() and >> anext() about 5 months ago (see https://bugs.python.org/issue31861). >> I've CC'ed them here. >> > > Looks like PyAiter_Check was added along with the aiter/anext builtins. I > agree it's unnecessary to check for __aiter__ in it, so I let's just fix it. > > > >> >> My own view: >> >> A. iter() doesn't check that the thing returned implements __next__, >> because it's not needed -- iterators having an __iter__ methor is a >> convention, not a requirement. >> > > Yeah. > > >> You shouldn't implement __iter__ returning something that doesn't >> implement __iter__ itself, because then "for x in iter(a)" would fail even >> though "for x in a" works. But you get an error, and anyone who implements >> something like that (or uses it) deserves what they get. People know about >> this convention and the ABC enforces it, so in practice it will be very >> rare that someone gets bitten by this. >> >> B. aiter() shouldn't need to check either, for exactly the same reason. I >> *suspect* (but do not know) that the extra check for the presence of >> __iter__ is simply an attempt by the implementer to enforce the convention. >> There is no *need* other than ensuring that "async for x in aiter(a)" works >> when "async for x in a" works. >> > > I agree. > [SNIP] > Bottom line: let's fix PyAiter_Check to only look for __anext__. It's a > new function so we can still fix it to reflect PyIter_Check and not worry > about anything. > I don't know if Pablo wants such a change in 3.10 since we are at rc2 at this point, so this might have to wait for 3.11 (although there's no deprecation here since it's a loosening of requirements so it could go in straight away).
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