New submission from Daniel Pope <[email protected]>:
The anext_awaitable object returned by anext(..., default) does not support
.send()/.throw(). It only supports __next__().
So we can pass messages from the suspending coroutine to the event loop but not
from the event loop to the suspending coroutine.
trio and curio rely on both directions working. (I don't know about asyncio.)
For example, this trio code fails:
import trio
async def produce():
for v in range(3):
await trio.sleep(1)
yield v
async def consume():
p = produce()
while True:
print(await anext(p, 'finished'))
trio.run(consume)
raising AttributeError: 'anext_awaitable' object has no attribute 'send'.
I realise that any awaitable that wants to await another awaitable must return
not an iterator from __await__() but something that implements the full PEP-342
generator protocol. Should PEP-492 section on __await__()[1] say something
about that?
[1] https://www.python.org/dev/peps/pep-0492/#await-expression
----------
components: Library (Lib)
messages: 399982
nosy: lordmauve
priority: normal
severity: normal
status: open
title: anext_awaitable is not a collections.abc.Generator
type: behavior
versions: Python 3.10, Python 3.11
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Python tracker <[email protected]>
<https://bugs.python.org/issue44963>
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