Add `pathlib._abc.PathModuleBase` (#113893)

Path modules provide a subset of the `os.path` API, specifically those
functions needed to provide `PurePathBase` functionality. Each
`PurePathBase` subclass references its path module via a `pathmod` class
attribute.

This commit adds a new `PathModuleBase` class, which provides abstract
methods that unconditionally raise `UnsupportedOperation`. An instance of
this class is assigned to `PurePathBase.pathmod`, replacing `posixpath`.
As a result, `PurePathBase` is no longer POSIX-y by default, and
all its methods raise `UnsupportedOperation` courtesy of `pathmod`.

Users who subclass `PurePathBase` or `PathBase` should choose the path
syntax by setting `pathmod` to `posixpath`, `ntpath`, `os.path`, or their
own subclass of `PathModuleBase`, as circumstances demand.

1 files changed, 1 insertions, 0 deletions

diff --git a/Lib/test/test_pathlib/test_pathlib.py b/Lib/test/test_pathlib/test_pathlib.py
index 1b560adfc3b..61d7939ad14 100644
--- a/Lib/test/test_pathlib/test_pathlib.py
+++ b/Lib/test/test_pathlib/test_pathlib.py
@@ -1151,6 +1151,7 @@ class PathTest(test_pathlib_abc.DummyPathTest, PurePathTest):
 
     def test_matches_pathbase_api(self):
         our_names = {name for name in dir(self.cls) if name[0] != '_'}
+        our_names.remove('is_reserved')  # only present in PurePath
         path_names = {name for name in dir(pathlib._abc.PathBase) if name[0] != '_'}
         self.assertEqual(our_names, path_names)
         for attr_name in our_names: