gh-128289: Add eager_tasks parameter to asyncio.run() and asyncio.Runner

[asvetlov]

• Issue: Add eager_tasks parameter to asyncio Runner and run() #128289

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📚 Documentation preview 📚: https://cpython-previews--128293.org.readthedocs.build/

[asvetlov]

@gvanrossum does the PR fit your vision?
Does eager_task argument sound good or there is better naming?

[asvetlov]

A failed hypothesis test for glob is definitely not related to the PR, it is broken in the main branch already.

[graingert]

This will also need some way to set this in IsolatedAsyncioTestCase

[asvetlov]

This will also need some way to set this in IsolatedAsyncioTestCase

Good idea. A classvar attribute with special name maybe, something like EAGER_TASKS = True.

I would update async test case when this PR will land.

[graingert]

Possibly we could stick to just using loop_factory for this and asyncio.Task can issue the deprecation warning if eager isn't set to True in the constructor. (We could use eager = True, False or None to decide the warning)

[asvetlov]

Possibly we could stick to just using loop_factory for this and asyncio.Task can issue the deprecation warning if eager isn't set to True in the constructor. (We could use eager = True, False or None to decide the warning)

Sorry, I don't follow how loop_factory is related to lazy/eager task creation.

Could you please elaborate?

[graingert]

Currently for 3.13 to enable eager tasks the approach is to do:

def loop_factory():
    loop = asyncio.EventLoop()
    loop.set_task_factory(asyncio.eager_task_factory)
    return loop

asyncio.run(amain(), loop_factory=loop_factory)

So this should still work and not trigger a deprecation warning

[asvetlov]

I consider loop.set_task_factory() as low-level function.
If a user overrides eager_tasks by set_task_factory() it is totally legal behavior, a user is free to do it on its own.

[graingert]

We could provide an eager loop factory and deprecate calling asyncio.Task(eager_start=None)

Code would look like asyncio.run(amain(), loop_factory=asyncio.eager_loop_factory)

[asvetlov]

I've got you finally, I hope.
Yes, it is a viable solution too.
Anyway, we should reach some conclusion in the discuss group first before any of PR will get a chance to be merged.