all deprecation warnings are disabled for the whole process while new unix asyncio subprocesses are created

[graingert]

on python3.10 the following prints:

python3.10 demo.py 
/home/graingert/projects/cpython/demo.py:40: DeprecationWarning: demo warning
  warnings.warn("demo warning", DeprecationWarning)
/home/graingert/projects/cpython/demo.py:48: DeprecationWarning: demo warning2
  warnings.warn("demo warning2", DeprecationWarning)

but on python main it prints:

./python demo.py      
/home/graingert/projects/cpython/demo.py:40: DeprecationWarning: demo warning
  warnings.warn("demo warning", DeprecationWarning)

import sys
import threading
import asyncio
import concurrent.futures
import warnings


async def acreate_process_then_sleep(started_event, stop_event):
    event = asyncio.Event()

    async def create_process():
        loop = asyncio.get_running_loop()
        loop.call_soon(event.set)
        proc = await asyncio.create_subprocess_exec(
            sys.executable,
            "-c",
            "print('hello')",
            stdin=None,
            stdout=asyncio.subprocess.PIPE,
            stderr=asyncio.subprocess.STDOUT,
        )
        await proc.communicate()

    async def sleep():
        await event.wait()
        started_event.set()
        stop_event.wait()

    await asyncio.gather(create_process(), sleep())


def create_process_then_sleep(*args, **kwargs):
    asyncio.run(acreate_process_then_sleep(*args, **kwargs))


def main():
    with concurrent.futures.ThreadPoolExecutor() as tpe:
        stop_event = threading.Event()
        started_event = threading.Event()
        warnings.warn("demo warning", DeprecationWarning)
        fut = tpe.submit(
            create_process_then_sleep,
            started_event=started_event,
            stop_event=stop_event,
        )
        try:
            started_event.wait()
            warnings.warn("demo warning2", DeprecationWarning)
        finally:
            stop_event.set()
            fut.result()


if __name__ == "__main__":
    sys.exit(main())

Originally posted by @graingert in https://github.com/python/cpython/pull/98215#discussion_r996426251

[graingert]

cc @kumaraditya303

[graingert]

see also https://github.com/python/cpython/issues/91505, https://github.com/python/cpython/issues/81785 and https://github.com/python/cpython/issues/50896

[kumaraditya303]

Okay, I'll be AFK for some time so feel free to create a PR. I doubt that any one will hit this in practise though.

[gvanrossum]

Ah, I guess I was right about that context manager. :-)

[kumaraditya303]

https://github.com/python/cpython/pull/98333 fixes this, I had underestimated warnings module :-)

[gvanrossum]

We're still looking for a perfect solution (see discussion in PR), so keeping this issue open.

[kumaraditya303]

I'm closing this as done with good enough, there are plenty of places in stdlib where this happens and in those places some real work in done rather than just a function call. No point in spending more time on this.