[Python-ideas] Introduce typing.SupportsFsPath

Ivan Levkivskyi levkivskyi at gmail.com
Thu Oct 11 16:47:46 EDT 2018

On Tue, 9 Oct 2018 at 15:17, Eric Fahlgren <ericfahlgren at gmail.com> wrote:

> On Tue, Oct 9, 2018 at 3:16 AM Ivan Levkivskyi <levkivskyi at gmail.com>
> wrote:
>> class PathLike(Protocol[AnyStr]):
> I had been working on this same problem intermittently for several months,
> so thanks, but...
>     error: Invariant type variable 'AnyStr' used in protocol where
> covariant one is expected
> is called out on the class  by mypy 0.630 (Python 3.6.6).  Do I just need
> to wait for 0.640?  Or should I define a new TypeVar for AnyStr_co and use
> that?

Hm, it looks like mypy overreacts here. I think it should be safe to use a
constrained type variable if there are no constraints that are subtypes of
other constraints (which is the case for AnyStr on Python 3, where bytes is
not a subtype of str). Could you please open an issue about this on mypy
tracker? In the meantime, you can just silence the error with a `# type:

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