GH-133789: Fix unpickling of pathlib objects pickled in Python 3.13 (#133831)

In Python 3.13 (but not 3.12 or 3.14), pathlib classes are defined in
`pathlib._local` rather than `pathlib`. In hindsight this was a mistake,
but it was difficult to predict how the abstract/local split would pan out.

In this patch we re-introduce `pathlib._local` as a stub module that
re-exports the classes from `pathlib`. This allows path objects pickled in
3.13 to be unpicked in 3.14+

Lib/pathlib/_local.py

@@ -0,0 +1,12 @@
+"""
+This module exists so that pathlib objects pickled under Python 3.13 can be
+unpickled in 3.14+.
+"""
+
+from pathlib import *
+
+__all__ = [
+    "UnsupportedOperation",
+    "PurePath", "PurePosixPath", "PureWindowsPath",
+    "Path", "PosixPath", "WindowsPath",
+]

Lib/test/test_pathlib/test_pathlib.py

@@ -293,6 +293,12 @@ def test_pickling_common(self):
                     self.assertEqual(hash(pp), hash(p))
                     self.assertEqual(str(pp), str(p))
 
+    def test_unpicking_3_13(self):
+        data = (b"\x80\x04\x95'\x00\x00\x00\x00\x00\x00\x00\x8c\x0e"
+                b"pathlib._local\x94\x8c\rPurePosixPath\x94\x93\x94)R\x94.")
+        p = pickle.loads(data)
+        self.assertIsInstance(p, pathlib.PurePosixPath)
+
     def test_repr_common(self):
         for pathstr in ('a', 'a/b', 'a/b/c', '/', '/a/b', '/a/b/c'):
             with self.subTest(pathstr=pathstr):

Misc/NEWS.d/next/Library/2025-05-10-15-10-54.gh-issue-133789.I-ZlUX.rst

@@ -0,0 +1 @@
+Fix unpickling of :mod:`pathlib` objects that were pickled in Python 3.13.