fix: FixFuture attached to different loop error on read_database_uri

[nameexhaustion]

• Reverts feat(python): Drop nest-asyncio in favor of custom logic #20793
• ref read_database since 1.21 with async oracledb throwing "got Future <Future pending> attached to a different loop" #21263
  • I don't have a local repro but this should fix

[ritchie46]

Hmm.. we also use this logic in polars_cloud. What does nest-async-io different? In polars_cloud I want to do this without dependencies.

[codecov]

Codecov Report

Attention: Patch coverage is 65.82278% with 54 lines in your changes missing coverage. Please review.

Project coverage is 80.53%. Comparing base (36c49ed) to head (91ac2e2).
Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
py-polars/polars/_utils/nest_asyncio.py	64.70%	41 Missing and 13 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21641      +/-   ##
==========================================
- Coverage   80.54%   80.53%   -0.01%     
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  Files        1603     1604       +1     
  Lines      231266   231395     +129     
  Branches     2650     2678      +28     
==========================================
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[nameexhaustion]

Hmm.. we also use this logic in polars_cloud. What does nest-async-io different? In polars_cloud I want to do this without dependencies.

nest-asyncio maintains the original loop when executing a nested task. The one we currently have doesn't -

# 1.20
_run_async 1.20.0 asyncio.get_running_loop() is original_loop = True
OK
# 1.21
_run_async 1.21.0 asyncio.get_running_loop() is original_loop = False
ERR: Task <Task pending name='Task-3' coro=<test() running at /Users/nxs/git/polars/.env/y.py:17> cb=[_run_until_complete_cb() at /Users/nxs/.pyenv/versions/3.12.2/lib/python3.12/asyncio/base_events.py:181]> got Future <Task pending name='Task-2' coro=<sleep() running at /Users/nxs/.pyenv/versions/3.12.2/lib/python3.12/asyncio/tasks.py:653>> attached to a different loop

Script -

import polars as pl
import asyncio
from polars.io.database._utils import _run_async


async def main():
    loop = asyncio.get_running_loop()
    task = loop.create_task(asyncio.sleep(0))
    _run_async(test(loop, task))


async def test(original_loop, task):
    print(
        f"_run_async {pl.__version__} {asyncio.get_running_loop() is original_loop = }"
    )
    try:
        await task
    except Exception as e:
        print(f"ERR: {str(e)}")
    else:
        print("OK")


if __name__ == "__main__":
    asyncio.run(main())

The underlying async driver is probably also creating objects that reference the original loop before we enter the nested context.