[issue37455] asyncio.run() error related to finalizing async generators

[Karthikeyan Singaravelan]

Change by Karthikeyan Singaravelan :


--
resolution:  -> duplicate
stage:  -> resolved
status: open -> closed
superseder:  -> AsyncGenerator breaks when not iterated fully with 
RuntimeError("can't send non-None value to a just-started coroutine")

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue37455] asyncio.run() error related to finalizing async generators

[Andrew Svetlov]

Andrew Svetlov  added the comment:

Yes, please close as a duplicate.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue37455] asyncio.run() error related to finalizing async generators

[Karthikeyan Singaravelan]

Karthikeyan Singaravelan  added the comment:

I think this would be fixed by issue38013. Andrew I feel these are the same 
issues here and can be closed.

--
nosy: +xtreak

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue37455] asyncio.run() error related to finalizing async generators

[Sam Frances]

Sam Frances  added the comment:

One final note: changing the `main()` function from the example to add a 
zero-sleep seems to fix it, but this seems like a rather ad-hoc solution.

```
async def main():
async for i in double(count()):
if i > 10:
break
print(i)
await asyncio.sleep(0)
```

result:

```
$ python example.py 
0
2
4
6
8
10
double() cleanup
count() cleanup
```

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue37455] asyncio.run() error related to finalizing async generators

[Sam Frances]

Sam Frances  added the comment:

Apologies for the stray unused function in the example. It should have read:

```
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 main():
async for i in double(count()):
if i > 10:
return
print(i)

asyncio.run(main())
```

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue37455] asyncio.run() error related to finalizing async generators

[Sam Frances]

New submission from Sam Frances :

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: ()> 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 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com