Add PathLike to typing

[ilevkivskyi]

While thinking about protocols, it came to my mind that we could add PathLike to typing, also we could make it a (runtime) protocol class. As I understand PEP 519, it could be typed like this:

S = TypeVar('S', bound=Union[str, bytes])
class PathLike(Generic[S], extra=os.PathLike): # or Protocol[S] in future
    def __fspath__(self) -> S:
        ...

So that there will be three allowed types: PathLike[str], PathLike[bytes], and PathLike[Union[str, bytes]]. Or we actually don't need PathLike[Union[str, bytes]]? In this case we could just use AnyStr instead of S.

CC @brettcannon

[JelleZijlstra]

FYI, PEP 519 explicitly rejects adding typing.PathLike (https://www.python.org/dev/peps/pep-0519/#provide-specific-type-hinting-support). But maybe the situation will change once we have protocols in the language.

I've also been thinking about this recently. In addition to PathLike, it would be nice to have a generic alias like typing.FSPath[AnyStr] so you don't have to write something like Union[AnyStr, PathLike[AnyStr]].

[brettcannon]

There's already https://docs.python.org/3/library/os.html#os.PathLike so it's part way there already.

And if/when protocols come into Python then there will be a discussion as to whether we should back-fill the stdlib with protocols and I suspect PathLike would be one of them.

[gvanrossum]

Hm, `os.PathLike` just landed in typeshed (see python/typeshed#991 and python/typeshed@41561f1 ). What else is there to do?

…

On Tue, Mar 21, 2017 at 10:16 AM, Brett Cannon ***@***.***> wrote: There's already https://docs.python.org/3/library/os.html#os.PathLike so it's part way there already. And if/when protocols come into Python then there will be a discussion as to whether we should back-fill the stdlib with protocols and I suspect PathLike would be one of them. — You are receiving this because you are subscribed to this thread. Reply to this email directly, view it on GitHub <#402 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/ACwrMroR5zdukbTuOognCdn57wt5nuLzks5roAX4gaJpZM4MjLiM> .

-- --Guido van Rossum (python.org/~guido)

[ilevkivskyi]

What else is there to do?

Two things:

• We could make it an actual generic, so that one can write path: PathLike[str]
• In the (not so distant) future, we could make it a protocol class.

[gvanrossum]

We could make it an actual generic, so that one can write path: PathLike[str]

Hm... So for a PathLike[str] the __fspath__() method returns str, and so on. This made me look more carefully at the code that I moved around, and I now realize that it returns AnyStr without taking any arguments using that type variable (nor is the class generic). That seems odd, and also it appears mypy arbitrarily picks str as the actual return type.

I think I know a fix and I'll send it to you.

[srittau]

It seems os.PathLike now works as suggested here.

[izzues]

So, what is the correct way to do it now?

[Gobot1234]

os.PathLike[str] or os.PathLike[bytes] as described in the original proposal