On Mon, Jan 17, 2022 at 7:02 AM Jelle Zijlstra <jelle.zijls...@gmail.com> wrote:
> > > El lun, 17 ene 2022 a las 6:25, Petr Viktorin (<encu...@gmail.com>) > escribió: > >> On Wed, Nov 17, 2021 at 8:31 AM Pradeep Kumar Srinivasan >> <gohan...@gmail.com> wrote: >> > >> > This PEP [1] introduces a simple and intuitive way to annotate methods >> and classmethods that return an instance of their class. Such methods and >> classmethods occur quite frequently, but the existing way to annotate them >> correctly is quite arcane and error-prone. The PEP introduces a special >> type `Self` to represent the type of the `self` parameter, similar to the >> `this` type in TypeScript and the `Self` type in Rust. We have >> implementations for mypy and pyright. The PEP does not affect CPython >> directly except for the addition of one special form (Self) to typing.py >> [2]. >> > >> > Since we have reached consensus on the PEP in typing-sig [3], we wanted >> to get your comments and suggestions before submitting to the Steering >> Council. >> > >> > Thanks, >> > Pradeep Kumar Srinivasan >> > James Hilton-Balfe >> > >> > [1]: https://www.python.org/dev/peps/pep-0673/ >> > [2]: Adding `Self` to typing_extensions.py: >> https://github.com/python/typing/pull/933 >> > [3]: See the comments from typing-sig members on the Google doc: >> https://docs.google.com/document/d/1ujuSMXDmSIOJpiZyV7mvBEC8P-y55AgSzXcvhrZciuI/edit?usp=sharing >> >> Hello, and thanks for the PEP! >> Sorry I'm late, but I have two curious questions about the PEP. >> I don't think they should hold back accepting the PEP, but I'm >> interested in the answers. >> >> The PEP uses `reveal_type`, a function that's appeared in a few PEPs >> already, but was never described. Is it a standard function in typing >> tools, something specific to mypy, or pseudocode? >> > > It's a function that doesn't exist at runtime, but when a type checker > sees a call, it emits the inferred type of the argument. It originated with > mypy but I believe has been adopted by all type checkers. > > There's been some talk of adding it to the `typing` module, but that > hasn't happened so far. I opened https://bugs.python.org/issue46414 to > suggest adding it. > Yes, it is a pseudo function that has been adopted afaik by all type checkers, e.g., Mypy, Pyre, Pyright. It's useful for debugging type errors by using `reveal_type(<expr>)` and running the type checker. I honestly didn't even realize that it wasn't specified in PEP 484 until you asked. Do you suggest adding an explanation in the PEP or is it reasonably self-explanatory? I see a few other PEPs using it. > >> >> The PEP says "we reject Self in metaclasses." >> "Metaclass" can mean "subclass of `type`", or it can refer to how a >> value is used -- for example, you can write `class >> Foo(metaclass=print): ...`. >> In the PEP's example, is MyMetaclass rejected because: >> - it's used as a metaclass in a class statement, or >> - it's a subclass of `type` (so it's rejected even if unused), or >> - it becomes a class of a class? >> Or is the exact interpretation best left to the type checker? >> > The PEP rejects `Self` used in `MyMetaclass` because the class is a subclass of `type`. So, there would be a type error even if `MyMetaclass` were unused. In general, the `# Rejected` comment indicates the position at which the type checker would emit a type error, as per the convention in other typing PEPs. So, in the PEP's metaclass example, we suggest that type errors be emitted at the uses of `Self` in the return annotations of `__new__` and `__mul__`. (The exact error and position is left up to the type checker.) Thanks for the questions! _______________________________________________ >> Python-Dev mailing list -- python-dev@python.org >> To unsubscribe send an email to python-dev-le...@python.org >> https://mail.python.org/mailman3/lists/python-dev.python.org/ >> Message archived at >> https://mail.python.org/archives/list/python-dev@python.org/message/DVOQK3U6MOYXPRXF5OVLVLJBPEJRUIM5/ >> Code of Conduct: http://python.org/psf/codeofconduct/ >> > -- S Pradeep Kumar
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