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

Jelle Zijlstra jelle.zijlstra at gmail.com
Thu May 25 10:30:38 EDT 2017

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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