File system path annotations

[Roel Schroeven]

Op 19/06/2023 om 10:43 schreef Peter Slížik via Python-list:
> Hello,
>
> what is the preferred way of annotating file system paths?
>
> This StackOverflow answer <https://stackoverflow.com/a/58541858/1062139>
> (and a few others) recommend using the
>
> str | os.PathLike
>
> union.
>
> However, byte arrays can be used as paths too, and including them
> would make the annotation quite long.
You don't have to type out the whole thing every time. Define it somewhere:

PathLike = str | bytes | os.PathLike

and then you can use PathLike everywhere.
> I also believe that str confirms to the PathLike definition. Please,
> correct me if I'm wrong.
I don't think so: os.PathLike instances must have a __fspath__() method, 
which str and bytes don't have.
> And finally - using paths in Python programs is so common, that one
> would expect to have a special type (or type alias) in typing. Am I
> missing something?
I agree there should be something like that. This StackOverflow answer 
(https://stackoverflow.com/a/68027757/59122) talks about something like 
that: _typeshed.AnyPath. It is used in the standard library, but 
apparently it doesn't exist at runtime and you need a trick to make it 
work. I would expect something better to exist, but as far as I can find 
out there isn't.

PEP 519 has a little section on the topic 
(https://peps.python.org/pep-0519/#provide-specific-type-hinting-support):

 > Provide specific type hinting support
 >
 > There was some consideration to providing a generic typing.PathLike 
class which would allow for e.g. typing.PathLike[str] to specify a type 
hint for a path object which returned a string representation.
 > While potentially beneficial, the usefulness was deemed too small to 
bother adding the type hint class.
 >
 > This also removed any desire to have a class in the typing module 
which represented the union of all acceptable path-representing types as 
that can be represented with typing.Union[str, bytes,
 > os.PathLike] easily enough and the hope is users will slowly 
gravitate to path objects only.

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