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

Guido van Rossum guido at python.org
Fri May 26 16:51:50 EDT 2017 
On Thu, May 25, 2017 at 7:19 AM, Nick Coghlan <ncoghlan at gmail.com> wrote:

> Given the abstract, I'd suggest "Structural Subtyping" as a suitable
> title for the PEP.
>

Maybe even "Structural Subtyping (a.k.a. Duck Typing)"



> 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.
>

Agreed.


> 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. Imports don't enter the matter. (Things get tied together at the call
sites.) @Ivan: if there isn't an example that makes this clear we should
add one.

-- 
--Guido van Rossum (python.org/~guido)
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