[Python-Dev] PEP 544: Protocols - second round (original) (raw)

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.

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