Fix instantiation of standalone FakePathlibModule

- needs a patched os in Python >= 3.11

Author: mrbean-bremen

CHANGES.md

@@ -27,7 +27,9 @@ The released versions correspond to PyPI releases.
   (see [#1121](../../issues/1121))
 * fixed workaround for recursion with pytest under Windows to ignore capitalization
   of pytest executable (see [#1096](../../issues/1096))
-* added missing `mode` property to fake file wrapper (see [#1162](../../issues/1096))
+* added missing `mode` property to fake file wrapper (see [#1162](../../issues/1162))
+* fixed instantiation of a standalone `FakePathlibModule` for Python >= 3.11
+  (see [#1169](../../issues/1169))
 
 ### Infrastructure
 * adapt test for increased default buffer size in Python 3.14a6

pyfakefs/fake_filesystem_unittest.py

@@ -775,17 +775,26 @@ def _init_fake_module_classes(self) -> None:
         # it by adding an attribute in fixtures/module_with_attributes.py
         # and a test in fake_filesystem_unittest_test.py, class
         # TestAttributesWithFakeModuleNames.
+
+        # we instantiate the fake pathlib library with `from_patcher` set
+        # to avoid faking pathlib.os (already faked by the patcher)
+        def fake_pathlib_module(fs: FakeFilesystem):
+            return fake_pathlib.FakePathlibModule(fs, from_patcher=True)
+
+        def fake_path_module(fs: FakeFilesystem):
+            return fake_pathlib.FakePathlibPathModule(fs, from_patcher=True)
+
         self._fake_module_classes = {
             "os": fake_os.FakeOsModule,
             "shutil": fake_filesystem_shutil.FakeShutilModule,
             "io": fake_io.FakeIoModule,
-            "pathlib": fake_pathlib.FakePathlibModule,
+            "pathlib": fake_pathlib_module,
         }
         if sys.version_info >= (3, 13):
             # for Python 3.13, we need both pathlib (path with __init__.py) and
             # pathlib._local (has the actual implementation);
             # depending on how pathlib is imported, either may be used
-            self._fake_module_classes["pathlib._local"] = fake_pathlib.FakePathlibModule
+            self._fake_module_classes["pathlib._local"] = fake_pathlib_module
         if IS_PYPY or sys.version_info >= (3, 12):
             # in PyPy and later cpython versions, the module is referenced as _io
             self._fake_module_classes["_io"] = fake_io.FakeIoModule2
@@ -813,7 +822,7 @@ def _init_fake_module_classes(self) -> None:
             self._unfaked_module_classes["pathlib2"] = fake_pathlib.RealPathlibModule
         if scandir:
             self._fake_module_classes["scandir"] = fake_legacy_modules.FakeScanDirModule
-        self._fake_module_classes["Path"] = fake_pathlib.FakePathlibPathModule
+        self._fake_module_classes["Path"] = fake_path_module
         self._unfaked_module_classes["Path"] = fake_pathlib.RealPathlibPathModule
 
     def _init_fake_module_functions(self) -> None:

pyfakefs/fake_pathlib.py

@@ -42,6 +42,7 @@
 import warnings
 from pathlib import PurePath
 from typing import Callable, List, Optional
+from unittest import mock
 from urllib.parse import quote_from_bytes as urlquote_from_bytes
 
 from pyfakefs import fake_scandir
@@ -554,6 +555,7 @@ def gethomedir(self, username):
 
         def compile_pattern(self, pattern):
             return re.compile(fnmatch.translate(pattern)).fullmatch
+
 else:  # Python >= 3.12
 
     class FakePosixPathModule(FakePathModule):
@@ -862,21 +864,45 @@ def _warn_is_reserved_deprecated():
 class FakePathlibModule:
     """Uses FakeFilesystem to provide a fake pathlib module replacement.
 
-    You need a fake_filesystem to use this::
+    Automatically created if using `fake_filesystem_unittest.TestCase`,
+    `fs` fixture, or the `patchfs` decorator.
+
+    For creating it separately, a `fake_filesystem` instance is needed::
 
         filesystem = fake_filesystem.FakeFilesystem()
         fake_pathlib_module = fake_pathlib.FakePathlibModule(filesystem)
     """
 
-    def __init__(self, filesystem):
+    def __init__(self, filesystem, from_patcher=False):
         """
         Initializes the module with the given filesystem.
 
         Args:
             filesystem: FakeFilesystem used to provide file system information
+            from_patcher: If `False` (the default), `pathlib.os` will be manually
+                patched using `FakeOsModule`. This allows to instantiate the class
+                manually for a test.
+                Will be set to `True` if instantiated from `Patcher`.
         """
         init_module(filesystem)
         self._pathlib_module = pathlib
+        self._os = None
+        self._os_patcher = None
+        if not from_patcher:
+            self.patch_os_module()
+
+    def patch_os_module(self):
+        if sys.version_info >= (3, 11) and not isinstance(os, FakeOsModule):
+            self._os = FakeOsModule(FakePath.filesystem)
+            pathlib_os = (
+                "pathlib._local.os" if sys.version_info[:2] == (3, 13) else "pathlib.os"
+            )
+            self._os_patcher = mock.patch(pathlib_os, self._os)
+            self._os_patcher.start()
+
+    def __del__(self):
+        if self._os_patcher is not None:
+            self._os_patcher.stop()
 
     class PurePosixPath(PurePath):
         """A subclass of PurePath, that represents non-Windows filesystem
@@ -990,9 +1016,9 @@ class FakePathlibPathModule:
 
     fake_pathlib = None
 
-    def __init__(self, filesystem=None):
+    def __init__(self, filesystem=None, from_patcher=False):
         if self.fake_pathlib is None:
-            self.__class__.fake_pathlib = FakePathlibModule(filesystem)
+            self.__class__.fake_pathlib = FakePathlibModule(filesystem, from_patcher)
 
     @property
     def skip_names(self):

pyfakefs/tests/fake_filesystem_test.py

@@ -2614,6 +2614,7 @@ def test_add_existing_real_paths_read_write(self):
 
     @unittest.skipIf(pytest is None, "pytest is not installed")
     @unittest.skipIf(sys.version_info < (3, 8), "importlib.metadata not available")
+    @unittest.skipIf("pathlib2" in sys.modules, "pathlib2 may break this test")
     def test_add_package_metadata(self):
         parent_path = pathlib.Path(pytest.__file__).parent.parent
         pytest_dist_path = parent_path / f"pytest-{pytest.__version__}.dist-info"

pyfakefs/tests/fake_pathlib_test.py

@@ -31,7 +31,8 @@
 from unittest.mock import patch
 
 from pyfakefs import fake_pathlib, fake_filesystem, fake_filesystem_unittest, fake_os
-from pyfakefs.fake_filesystem import OSType
+from pyfakefs.fake_filesystem import OSType, FakeFilesystem
+from pyfakefs.fake_pathlib import FakePathlibModule
 from pyfakefs.helpers import IS_PYPY, is_root
 from pyfakefs.tests.skipped_pathlib import (
     check_exists_pathlib,
@@ -1646,5 +1647,13 @@ def test_exists(self):
         self.assertTrue(check_exists_pathlib())
 
 
+class InstantiatedPathlibTest(unittest.TestCase):
+    def test_instantiated_pathlib(self):
+        fake_fs = FakeFilesystem()
+        fake_pathlib_module = FakePathlibModule(fake_fs)
+        top_level_dirs = list(fake_pathlib_module.Path("/").iterdir())
+        self.assertEqual(0, len(top_level_dirs))
+
+
 if __name__ == "__main__":
     unittest.main(verbosity=2)