Feature or enhancement

Proposal:

The asyncio policy system is deprecated in python 3.14 (#127949). As implemented, this includes the asyncio.set_event_loop() function. However, in 2022, it was decided that set_event_loop and get_event_loop (just the thread-local storage, not the broader policy system) were serving a useful and separate purpose and should be kept around. I relied on this decision in Tornado to adapt to various changes while staying on interfaces that I thought would be safe from deprecation.

I would like to briefly bring this up for reconsideration since this is a reversal of a decision from just a few years ago and it appears to have been lumped in with the rest of the policy system without consideration on its own.

If the decision to deprecate this function stands, I'll be able to adapt in Tornado, but it will be inconvenient: I think I'll have to use asyncio.Runner which was introduced in 3.11, while I'm still supporting 3.9 and 3.10 for another couple of years.

Background

Here's the history as I remember it. In Python 3.10, the policy system was deprecated and slated for removal in 3.12. When the 3.12 alphas were released with the policy methods removed, we found that there were code paths that relied on the deprecated methods without emitting suitable warnings, leading to surprise breakages. This caused everything to be reset (in 3.10.9 and 3.11.1, which is why those specific versions are cited in the docs). Deprecation notices were removed, but the understanding at the time was that this was just resetting the clock and policies would still be going away, just a few years later.

Separately, there was a debate about the set_event_loop function, although I can't find the right thread now. (#83710 (comment) and #98440 (comment) are related, but I can't find where the actual conclusion was reached). I think Jupyter was another project where set_event_loop turned out to be important?

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-130322: drop deprecation of asyncio.set_event_loop #132349