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pathlib ABCs: add protocols for supporting types #127456
Description
Activity
Penny for your thoughts on this @encukou :)
If you want to avoid adding a dependency on the typing module at runtime, you can use a similar technique to what we do with the protocol-like ABCs in
collections.abc,contextlibandos:- Use ABCs for the runtime implementation
- But add them to this allowlist in
typingso that the typing module treats them the same way it does protocol classes:Lines 1940 to 1948 in 328187c
- And in typeshed, pretend that they're protocols so that type checkers treat them identically to "actual" protocols
Reacted by Barney GaleThanks Alex - that will be useful when/if when make
PathBaseand friends public, but for now I might makepathlib._typesan "orphan" module that's imported by nothing else. This also lets me add type annotations for free. It's a bit similar towsgiref.types. Do you think I'm missing a pitfall with that approach?Oh, if that's the plan then that should be fine, yup!
Feature or enhancement
For typing and documentation purposes, it would be useful to define three protocols in pathlib:
Parser: likeos.path, but including only pure functionality that's essential forPurePathBaseDirEntry: likeos.DirEntry, but without some non-portable methods (likeinode())StatResult: likeos.stat_result, but without the tuple-like interface, and dropping non-essential attributesThese could be defined in a private module like
pathlib._types. For performance reasons that module shouldn't be imported by any other pathlib module.If/when we make
PathBasepublic, we'll also make these protocols public.See also: https://discuss.python.org/t/make-pathlib-extensible/3428/196
Linked PRs
Parser.sep#127725