Do not use weakrefs for fs objects in fake modules

- led to crashes of tests with manually created modules
- weakrefs should only be used for backlinks

Author: mrbean-bremen

CHANGES.md

@@ -2,6 +2,11 @@
 The released versions correspond to PyPI releases.
 `pyfakefs` versions follow [Semantic Versioning](https://semver.org/).
 
+## Unreleased
+
+### Fixes
+* do not use weakrefs for filesystem objects in fake modules
+  (see [#1284](https://github.com/pytest-dev/pyfakefs/issues/1284))
 
 ## [Version 6.1.1](https://pypi.python.org/pypi/pyfakefs/6.1.1) (2026-02-09)
 Fixes a packaging issue in latest version.

pyfakefs/fake_filesystem_shutil.py

@@ -34,7 +34,6 @@
 import os
 import shutil
 import sys
-import weakref
 from threading import RLock
 from collections.abc import Callable
 from typing import TYPE_CHECKING
@@ -70,24 +69,16 @@ def dir():
         """
         return ("disk_usage",)
 
-    def __init__(self, filesystem):
+    def __init__(self, filesystem: FakeFilesystem):
         """Construct fake shutil module using the fake filesystem.
 
         Args:
           filesystem:  FakeFilesystem used to provide file system information
         """
-        self._filesystem: weakref.ReferenceType[FakeFilesystem] = weakref.ref(
-            filesystem
-        )
+        self.filesystem = filesystem
         self.shutil_module = shutil
         self._patch_level = 0
 
-    @property
-    def filesystem(self) -> FakeFilesystem:
-        fs = self._filesystem()
-        assert fs is not None
-        return fs
-
     def _start_patching_global_vars(self):
         self._patch_level += 1
         if self._patch_level > 1:

pyfakefs/fake_io.py

@@ -21,7 +21,6 @@
 import _io  # pytype: disable=import-error
 import io
 import sys
-import weakref
 from enum import Enum
 from typing import (
     Any,
@@ -71,18 +70,10 @@ def __init__(self, filesystem: FakeFilesystem):
         Args:
             filesystem: FakeFilesystem used to provide file system information.
         """
-        self._filesystem: weakref.ReferenceType[FakeFilesystem] = weakref.ref(
-            filesystem
-        )
+        self.filesystem = filesystem
         self.skip_names: list[str] = []
         self._io_module = io
 
-    @property
-    def filesystem(self) -> FakeFilesystem:
-        fs = self._filesystem()
-        assert fs is not None
-        return fs
-
     def open(
         self,
         file: AnyStr | int,
@@ -98,10 +89,8 @@ def open(
         """Redirect the call to FakeFileOpen.
         See FakeFileOpen.call() for description.
         """
-        fs = self.filesystem
-        assert fs is not None
         return fake_open(
-            fs,
+            self.filesystem,
             self.skip_names,
             file,
             mode,
@@ -170,9 +159,7 @@ def __init__(self, filesystem: FakeFilesystem):
                 filesystem: FakeFilesystem used to provide file system
                     information (currently not used).
             """
-            self.filesystem: weakref.ReferenceType[FakeFilesystem] = weakref.ref(
-                filesystem
-            )
+            self.filesystem = filesystem
             self._fcntl_module = fcntl
 
         def fcntl(self, fd: int, cmd: int, arg: int = 0) -> int | bytes:
@@ -193,7 +180,7 @@ def lockf(
 
         def __getattribute__(self, name):
             """Prevents patching of skipped modules."""
-            fs: FakeFilesystem = object.__getattribute__(self, "filesystem")()
+            fs: FakeFilesystem = object.__getattribute__(self, "filesystem")
             if fs.has_patcher:
                 fnctl_module = object.__getattribute__(self, "_fcntl_module")
                 if is_called_from_skipped_module(

pyfakefs/fake_open.py

@@ -20,7 +20,6 @@
 import io
 import os
 import sys
-import weakref
 from collections.abc import Callable
 from stat import (
     S_ISDIR,
@@ -129,18 +128,10 @@ def __init__(
           filesystem:  FakeFilesystem used to provide file system information
           delete_on_close:  optional boolean, deletes file on close()
         """
-        self._filesystem: weakref.ReferenceType[FakeFilesystem] = weakref.ref(
-            filesystem
-        )
+        self.filesystem = filesystem
         self._delete_on_close = delete_on_close
         self.raw_io = raw_io
 
-    @property
-    def filesystem(self) -> FakeFilesystem:
-        fs = self._filesystem()
-        assert fs is not None
-        return fs
-
     def __call__(self, *args: Any, **kwargs: Any) -> AnyFileWrapper:
         """Redirects calls to file() or open() to appropriate method."""
         return self.call(*args, **kwargs)

pyfakefs/fake_os.py

@@ -24,7 +24,6 @@
 import os
 import sys
 import uuid
-import weakref
 from contextlib import contextmanager
 from stat import (
     S_IFREG,
@@ -154,22 +153,14 @@ def __init__(self, filesystem: FakeFilesystem):
         Args:
             filesystem: FakeFilesystem used to provide file system information
         """
-        self._filesystem: weakref.ReferenceType[FakeFilesystem] = weakref.ref(
-            filesystem
-        )
+        self.filesystem = filesystem
         self.os_module: Any = os
         self.path = FakePathModule(filesystem, self)
         self._supports_follow_symlinks: set | None = None
         self._supports_dir_fd: set | None = None
         self._supports_effective_ids: set | None = None
         self._supports_fd: set | None = None
 
-    @property
-    def filesystem(self) -> FakeFilesystem:
-        fs = self._filesystem()
-        assert fs is not None
-        return fs
-
     @property
     def devnull(self) -> str:
         return self.path.devnull

pyfakefs/fake_path.py

@@ -21,7 +21,6 @@
 import inspect
 import os
 import sys
-import weakref
 from stat import (
     S_IFDIR,
     S_IFMT,
@@ -113,19 +112,11 @@ def __init__(self, filesystem: FakeFilesystem, os_module: FakeOsModule):
         Args:
             filesystem: FakeFilesystem used to provide file system information
         """
-        self._filesystem: weakref.ReferenceType[FakeFilesystem] = weakref.ref(
-            filesystem
-        )
+        self.filesystem = filesystem
         self._os_path = self._OS_PATH_COPY
         self._os_path.os = self.os = os_module  # type: ignore[attr-defined]
         self.reset(filesystem)
 
-    @property
-    def filesystem(self) -> FakeFilesystem:
-        fs = self._filesystem()
-        assert fs is not None
-        return fs
-
     @classmethod
     def reset(cls, filesystem: FakeFilesystem) -> None:
         cls.sep = filesystem.path_separator
@@ -540,17 +531,9 @@ def __init__(self, filesystem: FakeFilesystem):
             """
             import nt  # type:ignore[import]
 
-            self._filesystem: weakref.ReferenceType[FakeFilesystem] = weakref.ref(
-                filesystem
-            )
+            self.filesystem = filesystem
             self.nt_module: Any = nt
 
-        @property
-        def filesystem(self) -> FakeFilesystem:
-            fs = self._filesystem()
-            assert fs is not None
-            return fs
-
         def getcwd(self) -> str:
             """Return current working directory."""
             return to_string(self.filesystem.cwd)