Indeed — we essentially lie to mypy about the method resolution order for list, dict, etc (mypy thinks that list directly inherits from collections.abc.MutableSequence — see the typeshed stub here: https://github.com/python/typeshed/blob/32bc2161a107db20c2ebc85aad31c29730db3e38/stdlib/builtins.pyi#L746), but numeric ABCs are not special-cased by typeshed in the same way as collections ABCs. Fundamentally, mypy has no knowledge about virtual subclassing.
Again, I covered this very comprehensively on StackOverflow ;) https://stackoverflow.com/questions/69334475/how-to-hint-at-number-types-i-e-subclasses-of-number-not-numbers-themselv/69383462#69383462 Best, Alex > On 16 Oct 2021, at 13:54, Steven D'Aprano <st...@pearwood.info> wrote: > > On Sat, Oct 16, 2021 at 09:54:13AM +0100, Alex Waygood wrote: >>>> On 16 Oct 2021, at 06:13, Steven D'Aprano <st...@pearwood.info> wrote: >>> Be careful about believing what you are told. >> Indeed, MyPy will correctly raise errors if you assign {None: []} to a >> variable annotated with dict[str, Number]. However, you'll find that >> MyPy also raises an error if you assign {'foo': 4} to a variable >> annotated with dict[str, Number]: > > Hah, serves me right for not testing it for both positive and negative > cases. > > In my very limited testing now, I see that the problem appears to be > with the Number type. mypy correctly accepts this: > > Data = Dict[str, int] > a: Data = {'spam': 42} > > (no errors), but if you change the annotation to use Number instead of > int, it wrongly flags that as a type error. > > Possibly mypy doesn't know that ints and floats are instances of Number? > > _______________________________________________ > Python-ideas mailing list -- python-ideas@python.org > To unsubscribe send an email to python-ideas-le...@python.org > https://mail.python.org/mailman3/lists/python-ideas.python.org/ > Message archived at > https://mail.python.org/archives/list/python-ideas@python.org/message/FJY3QKAUJOJYTODMZH72X2ZS63GKT6AN/ > Code of Conduct: http://python.org/psf/codeofconduct/ _______________________________________________ Python-ideas mailing list -- python-ideas@python.org To unsubscribe send an email to python-ideas-le...@python.org https://mail.python.org/mailman3/lists/python-ideas.python.org/ Message archived at https://mail.python.org/archives/list/python-ideas@python.org/message/JFS65SMVETZ7W4KARJYJUNP6KA5XOFPL/ Code of Conduct: http://python.org/psf/codeofconduct/
