New submission from Sam Frances <s...@samfrances.uk>:
The documentation for `asyncio.run()` states:
"This function runs the passed coroutine, taking care of managing the asyncio
event loop and finalizing asynchronous generators."
However, the following example seems to indicate that async generators are not
being cleared up correctly.
```
import asyncio
async def count():
try:
i = 0
while True:
yield i
i += 1
finally:
print("count() cleanup")
async def double(source):
try:
async for n in source:
yield n * 2
finally:
print("double() cleanup")
async def anext(aiter):
return await aiter.__anext__()
async def main():
async for i in double(count()):
if i > 10:
return
print(i)
asyncio.run(main())
```
The result is:
```
$ python example.py
0
2
4
6
8
10
unhandled exception during asyncio.run() shutdown
task: <Task finished name='Task-2' coro=<<async_generator_athrow without
__name__>()> exception=RuntimeError("can't send non-None value to a
just-started coroutine")>
RuntimeError: can't send non-None value to a just-started coroutine
count() cleanup
```
The above error is from Python 3.8.0b1+, but the exact same error occurs in
Python 3.7.
I'm not sure if this is a bug or if I am misunderstanding the intended
behaviour of `asyncio.run()`, but the behaviour was certainly surprising to me.
----------
components: asyncio
messages: 346943
nosy: asvetlov, samfrances, yselivanov
priority: normal
severity: normal
status: open
title: asyncio.run() error related to finalizing async generators
type: behavior
versions: Python 3.7, Python 3.8
_______________________________________
Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue37455>
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