[Python-Dev] PEP 544: Protocols - second round

[Jelle Zijlstra]

2017-05-25 7:19 GMT-07:00 Nick Coghlan <ncoghlan at gmail.com>:

> On 25 May 2017 at 21:26, Antoine Pitrou <solipsis at pitrou.net> wrote:
> > On Wed, 24 May 2017 23:31:47 +0200
> > Ivan Levkivskyi <levkivskyi at gmail.com> wrote:
> >
> >> Hi all,
> >>
> >> After collecting suggestions in the previous discussion on python-dev
> >> https://mail.python.org/pipermail/python-dev/2017-
> March/thread.html#147629
> >> and playing with implementation, here is an updated version of PEP 544.
> >>
> >> --
> >> Ivan
> >>
> >>
> >> A link for those who don't like reading long e-mails:
> >> https://www.python.org/dev/peps/pep-0544/
> >>
> >> =========================
> >>
> >> PEP: 544
> >> Title: Protocols
> >
> > Can you give this PEP a more explicit title? "Protocols" sound like
> > network protocols to me.
>
> Especially given the existing use of the term in an asyncio context:
> https://www.python.org/dev/peps/pep-3156/#transports-and-protocols
>
> Given the abstract, I'd suggest "Structural Subtyping" as a suitable
> title for the PEP.
>
> That said, I think it's fine to use "protocol" throughout the rest of
> the PEP as is currently the case - object protocols and network
> protocols are clearly different things, it's just the bare word
> "Protocols" appearing as a PEP title in the PEP index with no other
> context that's potentially confusing.
>
> I'm +1 on the general idea of the PEP, and only have one question
> regarding the specifics. Given:
>
>     import typing
>
>     class MyContainer:
>         def __len__(self) -> int:
>             ...
>         def close(self) -> None:
>             ...
>
> Would that be enough for a static typechecker to consider MyContainer
> a structural subtype of both typing.Sized and SupportsClose from the
> PEP, even though neither is imported explicitly into the module? I'm
> assuming the answer is "Yes", but I didn't see it explicitly stated
> anywhere.
>
> Yes, that should be the case. Specifically, if you pass a MyContainer
object to a function whose argument is annotated as typing.Sized or
SupportsClose, a type checker should accept that call.


> Cheers,
> Nick.
>
>
>
> --
> Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia
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