On Sun, Aug 29, 2021 at 2:01 PM Serhiy Storchaka <storch...@gmail.com> wrote:
> 29.08.21 23:16, Brett Cannon пише: > > If you look at > > > https://github.com/python/cpython/blob/b11a951f16f0603d98de24fee5c023df83ea552c/Python/ceval.c#L2409-L2451 > > < > https://github.com/python/cpython/blob/b11a951f16f0603d98de24fee5c023df83ea552c/Python/ceval.c#L2409-L2451 > > > > you will see that `async for` requires that the iterator returned from > > `__aiter__` define `__anext__`. But if you look at aiter() which uses > > PyObject_GetAiter() from > > > https://github.com/python/cpython/blob/f0a6fde8827d5d4f7a1c741ab1a8b206b66ffd57/Objects/abstract.c#L2741-L2759 > > < > https://github.com/python/cpython/blob/f0a6fde8827d5d4f7a1c741ab1a8b206b66ffd57/Objects/abstract.c#L2741-L2759 > > > > and PyAiter_Check() from > > > https://github.com/python/cpython/blob/f0a6fde8827d5d4f7a1c741ab1a8b206b66ffd57/Objects/abstract.c#L2769-L2778 > > < > https://github.com/python/cpython/blob/f0a6fde8827d5d4f7a1c741ab1a8b206b66ffd57/Objects/abstract.c#L2769-L2778 > > > > you will notice that aiter() requires `__anext__` *and* `__aiter__` on > > the async iterator that gets returned from __aiter__. > > > > Now the docs for aiter() at > > https://docs.python.org/3.10/library/functions.html#aiter > > <https://docs.python.org/3.10/library/functions.html#aiter> points out > > that the async iterator is expected to define both methods as does the > > glossary definition for "asynchronous iterator" > > (https://docs.python.org/3.8/glossary.html#term-asynchronous-iterator > > <https://docs.python.org/3.8/glossary.html#term-asynchronous-iterator>). > > > > So my question is whether the discrepancy between what `async for` > > expects and what `aiter()` expects on purpose? > > https://bugs.python.org/issue31861 <https://bugs.python.org/issue31861> > > was the issue for creating aiter() and I didn't notice a discussion of > > this difference. The key reason I'm asking is this does cause a > > deviation compared to the relationship between `for` and `iter()` (which > > does not require `__iter__` to be defined on the iterator, although > > collections.abc.Iterator does). It also makes the glossary definition > > being linked from > > > https://docs.python.org/3.10/reference/compound_stmts.html#the-async-for-statement > > < > https://docs.python.org/3.10/reference/compound_stmts.html#the-async-for-statement > > > > incorrect. > > PyIter_Check() only checks existence of __next__, not __iter__ (perhaps > for performance reasons). > Or maybe no one thought to require __iter__ for iterators? > > I just ported changes from PyPy in SQLite tests > (https://github.com/python/cpython/pull/28021) because a test class with > __next__ but without __iter__ passed tests on CPython but failed on PyPy. > I'm going to wait to hear from anyone who may have been involved with implementing aiter() and `async for` before proposing various ways to align them with iter() and `for`.
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