> Honestly I think it's pretty crazy and out there to have multiple event
loops in the same thread. That feels like an anti-pattern inspired by some
other event loop APIs (in other languages) that encourage this. But asyncio
was not designed for that.

I agree.

OTOH, if you're designing a library for asyncio, you want it to be as foolproof as possible, so many people simply pass an event loop everywhere.  It's especially annoying when you have a huge chunk of code that didn't need the loop, and then when something needs it you have to refactor everything or use "get_event_loop".

In terms of performance, I don't think this is gonna affect anything, it's just a couple of additional thread-local sets in the Loop.run method.

And we can design "get_running_loop" to raise a clear exception if no loop is currently running.