Kwargs, positional-only parameters and ParamSpec in asyncio

Async-SIG
1

Most asyncio scheduling functions don’t allow passing keyword arguments. To do that, use functools.partial()

I’d like to be able to type annotate these scheduling methods like run_in_executor, call_soon with ParamSpec, however because they do not take kwargs it’s not possible:

see: mypy Playground

adding support for kwargs via positional-only parameters allows ParamSpec to work:
mypy Playground however it would be a breaking change when passing executor and func as kwargs and no other args:

>>> await asyncio.get_running_loop().run_in_executor(executor=None, func=sync_fn)

an additional caveat is that this would also have to change how Context is passed to these callbacks, eg: mypy Playground

2

The higher-level asyncio.to_thread is now typed with ParamSpec: add ParamSpec to asyncio.to_thread by graingert · Pull Request #6668 · python/typeshed · GitHub

3

Changing signatures to use positional-only arguments is not an option, it is a breaking change as you mentioned.

Maybe ParamSpec should be extended to accept *args only without **kwargs?
It is a pretty normal use case IMHO, useful not only to asyncio itself.