On Wed, Dec 22, 2021 at 3:24 PM Nathaniel Smith <njs@pobox.com> wrote:

On Wed, Dec 22, 2021 at 7:13 AM Steven Troxler <steven.troxler@gmail.com> wrote:
>
> Pradeep, Guido and I are leaning toward removing the `async` part of PEP 677.
>
> There are several reasons:
> - If we leave `async` in, then `async (int) -> bool` and `(int) -> Awaitable[bool]` are the same
>    - This violates that there should only be one obvious way to do things
>    - It also might lead to a mismatch between written types and the errors returned by type
>       checkers, leading to unnecessary confusion
> - It looks like < 5% of callable types return Awaitable anyway
> - It has explicitly been brought up in python-dev as unnecessary complexity, and we largely
>   agree with this criticism.

For sync programs, it doesn't matter what we do, because they'll never
write `async` or `Awaitable`. For async programs, having to put
`Awaitable` everywhere adds a lot of visual noise. Most Python
programs are sync, so any async-related syntax is necessarily going to
be rare in absolute terms, but that's not really the relevant audience
to think about.

For modern code, `Awaitable` isn't used at definition point: you just
write `async def foo(a: int) -> bool`. So keeping it in PEP 677 would
make definition syntax and callable type syntax more consistent. I
think it's a big win for usability.

I also don't think it violates "one obvious way" -- emphasis on
"obvious" :-). With PEP 677 as currently written, using `async`
everywhere is the "obvious" way; `Awaitable` becomes a detail that
only type nerds have to think about.

While I agree with the overall philosophy here, the async keyword in annotation context is a syntax addition that could be deferred until after PEP 677 to appear in a later version.

As a side note, Awaitable is available from the typing module where typing users are already importing a pile from, as well as collections.abc.  But they appear to be different things.  Eek. `typing.Awaitable` vs `<class 'collections.abc.Awaitable'>`.

-gps

 

-n

--
Nathaniel J. Smith -- https://vorpus.org
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