Release Notes¶

pyfakefs Release Notes¶

The released versions correspond to PyPI releases. pyfakefs versions follow Semantic Versioning.

Version 6.2.0 (2026-04-12)¶

Changes the MRO for file wrappers.

Changes¶

fake file wrappers now derive from io.TextIOBase or io.BufferedIOBase, so that isinstance-checks for these classes succeed (see #1307 and #484)

Fixes¶

route some pseudo-devices to the system instead of patching them; this ensures that os.urandom and related functions work correctly with PyPy (see #1300)
fake file seek method did not return the location in the file (see #1304)
make sure case sensitivity is correctly set for fake posix paths in hash(), Path.match and Path.full_match (see #1308)

Infrastructure¶

use newest pytest for testing in CI

Version 6.1.6 (2026-03-18)¶

Follow-up bugfix release for 6.1.5.

Fixes¶

os.path.realpath did not correctly handle some absolute paths under Windows (previous fix was incomplete, see #1296)

Version 6.1.5 (2026-03-15)¶

Minor bugfix release.

Fixes¶

os.path.realpath did not resolve symlinks under Windows (see #1296)

Version 6.1.4 (2026-03-04)¶

Fixes incompatibility with VCCode unittest runner.

Fixes¶

expanduser now correctly handles paths besides home and different separators (see #1289)
avoid faking filesystem in VSCode unittest runner (see #1285)

Version 6.1.3 (2026-03-01)¶

Minor bugfix release.

Fixes¶

handle expanduser() and home() correctly in cross OS usage (see #1289)

Version 6.1.2 (2026-02-22)¶

Fixes a regression caused by the introduced weakrefs.

Fixes¶

do not use weakrefs for filesystem objects in fake modules (see #1284)

Version 6.1.1 (2026-02-09)¶

Fixes a packaging issue in latest version.

Fixes¶

fixed packaging issue: tests had not been added to sdist (see #1278)

Version 6.1.0 (2026-02-06)¶

Changes back-link references to weak references.

Changes¶

added more support for PyPy 3
Caution: many back-link references have been replaced by weak references; this may have unwanted consequences (crashes) for some untested workflows

Infrastructure¶

added PyPy 3.11 to CI, added PyPy builds for all OSes
use only pyproject.toml for dependencies, moved tox configuration into pyproject.toml

Fixes¶

fixed a problem accessing size from a FakeFileWrapper object (see #1276)
fixed a problem with readable raising an error on a file object. (see #1265)
avoid memory accumulation in consecutive tests by using weak references (see #1267)

Version 6.0.0 (2025-12-21)¶

Removes some deprecated functionality, removes support for Python < 3.10.

Breaking Changes¶

removed support for Python versions < 3.10; patch releases based on pyfakefs 5.10 supporting older versions may be made on demand
removed support for patching legacy modules scandir and pathlib2
changed the default for FakeFilesystem.shuffle_listdir_results to True to reflect the real filesystem behavior

Changes¶

added some support for Python 3.15a3

Fixes¶

fixes a problem with Path type hints using the pipe symbol in wrapped functions inside an fs dependent fixture (see #1242)
fixes problem with new coverage in Python 3.14 using the fake filesystem (see #1245)

Documentation¶

added project information to documentation pages

Infrastructure¶

added CI tests for Python 3.15

Version 5.10.2 (2025-11-04)¶

Fixes a problem with pathlib.glob in Python 3.14.

Fixes¶

fixed pathlib.glob() for Python 3.14 (see #1239)

Version 5.10.1 (2025-10-27)¶

Fixes a regression introduced in version 5.9.0.

Fixes¶

fixed a deadlock in shutil.copytree if copying using an shutil function as copy_function argument (see #1235)

Version 5.10.0 (2025-10-11)¶

Adds official support for Python 3.14. Last minor version before the 6.0 release.

Changes¶

the errno codes set in OSError have changed for some specific error conditions in Windows 11/Windows Server 2025; pyfakefs now matches this behavior instead of the previous behavior under Windows 10
added official support for Python 3.14

Enhancements¶

added support for os.readinto in Python 3.14
added support for pathlib.copy and pathlib.copy_into in Python 3.14

Fixes¶

fixes patching of Debian-specific tempfile in Python 3.13 (see #1214)

Version 5.9.3 (2025-08-28)¶

Fixes a utility method.

Changes¶

a warning is now issued if trying to create a nested fake filesystem with custom arguments (custom arguments are ignored in this case, as the existing fake filesystem is used)

Fixes¶

fixed fake_filesystem.add_package_metadata that had never worked correctly (see #1205)

Infrastructure¶

updated the package build-system minimum version to setuptools v61.2 and higher

Version 5.9.2 (2025-07-30)¶

Fixes interaction with pytest.

Fixes¶

fixed an interaction problem of fs with other pytest fixtures (see #1200)

Infrastructure¶

fixed some warnings in tests (see #1190)

Version 5.9.1 (2025-06-23)¶

Fixes regression in packaging in version 5.9.0.

Fixes¶

fixed handling of added strict argument in Python 3.9.23
make sure test files are packaged (see #1186)

Version 5.9.0 (2025-06-21)¶

Adds support for an API change in latest Python patch releases.

Changes¶

the message from an OSError raised in the fake filesystem has no longer the postfix “in the fake filesystem” (see #1159)
changed implementation of FakeShutilModule to prepare it for usage without the patcher (see #1171)

Enhancements¶

added convenience function add_package_metadata to add the metadata of a given package to the fake filesystem (see #1155)

Fixes¶

fixed handling of dynamic imports from code in the fake filesystem in Python > 3.11 (see #1121)
fixed workaround for recursion with pytest under Windows to ignore capitalization of pytest executable (see #1096)
added missing mode property to fake file wrapper (see #1162)
fixed instantiation of a standalone FakePathlibModule for Python >= 3.11 (see #1169)
added support for new value “ALLOW_MISSING” of strict argument in os.path.realpath (introduced in latest patch version of Python >= 3.10, see #1180)

Infrastructure¶

adapt test for increased default buffer size in Python 3.14a6
replace session-scoped with module-scoped fixture in test, run pytest over all tests in docker containers (see #1151)
remove setup.py and setup.cfg in favor of pyproject.toml

Version 5.8.0 (2025-03-11)¶

Adds preliminary support for Python 3.14.

Changes¶

added some preliminary support for Python 3.14
change behavior of FakeFilesystem.get_object() to ignore permissions as it has been before version 5.4.0 (see #1122)

Fixes¶

fixed a problem with flushing if writing over the buffer end (see #1120)
fixed a regression that could break tests under Posix in Python 3.12 (see #1126)
fixed behavior for os.access for symlinks under Windows
fixed permission problem on querying file properties (see #1122)
fixed patching in pytest setup phase for module and session-scoped fs fixtures (see #1126)

Documentation¶

use a theme for documentation supporting dark mode

Version 5.7.4 (2025-01-14)¶

Minor bugfix release.

Fixes¶

fixed a problem with module and session scoped fixtures in Python 3.13 (see #1101)
fixed handling of cwd if set to a pathlib.Path (see #1108)
fixed documentation for cleanup handlers, added convenience handler reload_cleanup_handler (see #1105)

Version 5.7.3 (2024-12-15)¶

Fixes a regression in version 5.7.3.

Fixes¶

fixed a regression in version 5.7.2 that tempfile was not patched after pause/resume (POSIX only, see #1098)
added workaround for a recursion occurring if using pytest under Windows and Python >= 3.12 (see #1096)

Infrastructure¶

run pytest-specific tests for all supported Python versions
pytest is only supported for versions >= 6.2.5, earlier version do not work in Python >= 3.10 due to a pytest issue - adapted tests and documentation

Version 5.7.2 (2024-12-01)¶

Fixes some problems with patching.

Fixes¶

added some support for loading fake modules in AUTO patch mode using importlib.import_module (see #1079)
added some support to avoid patching debugger related modules (see #1083)

Performance¶

avoid reloading tempfile in Posix systems

Infrastructure¶

use trusted publisher for release (see https://docs.pypi.org/trusted-publishers/)

Version 5.7.1 (2024-08-13)¶

Fixes a regression in version 5.7.0 that broke patching fcntl.

Fixes¶

fixes a regression that caused unfaked fcntl calls to fail (see #1074)

Version 5.7.0 (2024-08-10)¶

Adds official Python 3.13 support, improves OS emulation behavior.

Changes¶

officially support Python 3.13

Enhancements¶

the additional_skip_names parameter now works with more modules (see #1023)
added support for os.fchmod, allow file descriptor argument for os.chmod only for POSIX for Python < 3.13

Performance¶

avoid reloading glob in Python 3.13

Fixes¶

removing files while iterating over scandir results is now possible (see #1051)
fake pathlib.PosixPath and pathlib.WindowsPath now behave more like in the real filesystem (see #1053)
PurePosixPath reported Windows reserved names as reserved in Python >= 3.12 (see #1067)
PurePosixPath.joinpath() incorrectly handled paths with drives under Windows in Python >= 3.12 (see #1070)

Version 5.6.0 (2024-07-12)¶

Adds preliminary Python 3.13 support.

Enhancements¶

added preliminary support for Python 3.13 (tested with beta2) (see #1017)
added apply_umask argument to FakeFilesystem.create_dir to allow ignoring the umask (see #1038)

Fixes¶

use real open calls for remaining pathlib functions so that it works nice with skippedmodules (see #1012)

Infrastructure¶

Add pyupgrade as a pre-commit hook.

Version 5.5.0 (2024-05-12)¶

Deprecates the usage of pathlib2 and scandir.

Changes¶

The usage of the pathlib2 and scandir modules in pyfakefs is now deprecated. They will now cause deprecation warnings if still used. Support for patching these modules will be removed in pyfakefs 6.0.
PureWindowsPath and PurePosixPath now use filesystem-independent path separators, and their path-parsing behaviors are now consistent regardless of runtime platform and/or faked filesystem customization (see #1006).

Fixes¶

fixed handling of Windows pathlib paths under POSIX and vice verse (see #1006)
correctly use real open calls in pathlib for skipped modules (see #1012)

Version 5.4.1 (2024-04-11)¶

Fixes a regression.

Fixes¶

fixed a regression from version 5.4.0 that incorrectly handled files opened twice via file descriptor (see #997)

Version 5.4.0 (2024-04-07)¶

Improves permission handling.

Changes¶

the handling of file permissions under Posix should now mostly match the behavior of the real filesystem, which may change the behavior of some tests
removed the argument module_cleanup_mode, that was introduced as a temporary workaround in the previous version - related problems shall be handled using a cleanup handler

Enhancements¶

added support for O_NOFOLLOW and O_DIRECTORY flags in os.open (see #972 and #974)
added support for fake os.dup, os.dup2 and os.lseek (see #970)

Fixes¶

fixed a specific problem on reloading a pandas-related module (see #947), added possibility for unload hooks for specific modules
use this also to reload django views (see #932)
fixed EncodingWarning for Python >= 3.11 (see #957)
consider directory ownership while adding or removing directory entries (see #959)
fixed handling of directory enumeration and search permissions under Posix systems (see #960)
fixed creation of the temp directory in the fake file system after a filesystem reset (see #965)
fixed handling of dirfd in os.symlink (see #968)
add missing follow_symlink argument to os.link (see #973)
fixed handling of missing attribute in os.getxattr (see #971)
fixed permission problem with shutil.rmtree if emulating Windows under POSIX (see #979)
fixed handling of errors on opening files via file descriptor (see #967)
fixed handling of umask - it is now applied by default
fixed behavior of os.makedirs (see #987)

Infrastructure¶

replace undefined by own minimal implementation to avoid importing it (see #981)

Version 5.3.5 (2024-01-30)¶

Fixes a regression.

Fixes¶

Fixed a regression due to the changed behavior of the dynamic patcher cleanup (see #939). The change is now by default only made if the django module is loaded, and the behavior can be changed using the new argument module_cleanup_mode.

Packaging¶

included tox.ini and a few more files into the source distribution (see #937)

Version 5.3.4 (2024-01-19)¶

Bugfix release.

Fixes¶

fixed handling of unhashable modules which cannot be cached (see #923)
reload modules loaded by the dynamic patcher instead of removing them - sometimes they may not be reloaded automatically (see #932)
added back argument use_dynamic_patch as a fallback for similar problems

Version 5.3.2 (2023-11-30)¶

Bugfix release.

Fixes¶

fixed a problem with patching _io under Python 3.12 (see #910)
fixed a problem with accessing the temp path if emulating Linux under Windows (see #912)
fixed result of os.walk with a path-like top directory (see #915)
properly fixed the problem that filesystem patching was still active in the pytest logreport phase (see #904), the previous fix was incomplete

Version 5.3.1 (2023-11-15)¶

Mostly a bugfix release.

Changes¶

changed behavior of add_real_directory to be able to map a real directory to an existing directory in the fake filesystem (see #901)

Fixes¶

fixed the problem that filesystem patching was still active in the pytest logreport phase (see #904)
restored compatibility with PyTorch 2.0 and above, as well as with other classes that have custom setattr methods (see #905)

Version 5.3.0 (2023-10-11)¶

Adds official support for Python 3.12.

Changes¶

added official support for Python 3.12

Fixes¶

removed a leftover debug print statement (see #869)
make sure tests work without HOME environment set (see #870)
automount drive or UNC path under Windows if needed for pathlib.Path.mkdir() (see #890)
adapted patching io.open and io.open_code to work with Python 3.12 (see #836 and #892)

Version 5.2.4 (2023-08-18)¶

Fixes a rare problem on pytest shutdown.

Fixes¶

Clear the patched module cache on session shutdown (pytest only) (see #866). Added a class method Patcher.clear_fs_cache for clearing the patched module cache.

Version 5.2.3 (2023-07-10)¶

Adds compatibility with PyPy 3.10 and Python 3.12.

Fixes¶

Re-create temp directory if it had been created before on resetting file system (see #814).
Excluded pytest pathlib modules from patching to avoid mixup of patched/unpatched code (see #814).
Adapted to changes in Python 3.12 beta1 (only working partially, see #830 and #831).
Adapted to changes in shutil in Python 3.12 beta2 (see #814).
Fixed support for newer PyPi versions (see #859).

Documentation¶

Added a note regarding the incompatibility of the built-in sqlite3 module with pyfakefs (see #850)

Infrastructure¶

Added pytype check for non-test modules in CI (see #599).
Added tests for different pypy3 versions.
Added codespell hook to pre-commit

Version 5.2.2 (2023-04-13)¶

Fixes a regression in 5.2.0

Changes¶

Made the user and group IDs accessible via dedicated get_uid and get_gid functions (for symmetry to set_uid / set_gid)

Fixes¶

The test fixture is now included in the source distribution and installed with the package.
Some public constants in fake_filesystem that had been moved to helpers are made accessible from there again (see #809).
Add missing fake implementations for os.getuid and os.getgid (Posix only)
Make sure a /tmp path exists under linux (TMPDIR may point elsewhere) (see #810)

Version 5.2.1 (2023-04-11)¶

Support for latest Python 3.12 version.

Changes¶

Adapted fake pathlib to changes in Python 3.12a7 (last alpha version)

Fixes¶

Properties defining the capabilities of some os functions like os.supports_follow_symlinks are now properly faked to contain the fake functions if the real functions are faked (see #799)

Version 5.2.0 (2023-03-31)¶

Supports current Python 3.12 version (alpha 6). We plan to make patch releases in case of breaking changes in alpha or beta versions.

Changes¶

Fake module classes previously defined in fake_filesystem have now moved to their own modules: fake_os.FakeOsModule, fake_path.FakePathModule, fake_io.FakeIoModule and fake_open.FakeFileOpen. Additionally, all fake file classes have been moved to fake_file. While most of the changes shall be upwards compatible, we cannot exclude that we missed some problems.
Under macOS, at test start a symlink /tmp to the actual temporary directory is now created in the fake filesystem.
Patching of parsers for pandas >= 1.2 is removed since pandas now uses Python fs functions internally even when the engine selected is “c”.

Features¶

added possibility to set a path inaccessible under Windows by using chown() with the force_unix_mode flag (see #720)
added support for current Python 3.12 version (alpha 6)
added support for os.path.splitroot (new in Python 3.12)

Version 5.1.0 (2023-01-12)¶

New version before Debian freeze

Features¶

added class level setup method setUpClassPyfakefs for unittest and class-scoped fixture fs_class for pytest (see #752)
added experimental support for Python 3.12: added fake APIs for Windows junction support. These are not implemented and always return False.

Infrastructure¶

replaced end-of-life CentOS with RedHat UBI9 docker image
added tests for pytest 7.2.0
added black to pre-commit checks, which caused some changes to the coding style (max line length is now 88, always use double quotes)
added Python 3.12 to the test suite.
migrated to setuptools declarative syntax.
fixed docker tests when running on branches containing forward slashes

Version 5.0.0 (2022-10-09)¶

New version after the transfer to pytest-dev.

Changes¶

the old-style API deprecated since version 3.4 has now been removed
the method copyRealFile deprecated since version 3.2 has been removed - use add_real_file instead

Infrastructure¶

transferred the repository to the pytest-dev organization
renamed the master branch to main
added automatic PyPI release workflow
move documentation from GitHub Pages to Read the Docs

New Features¶

added some support for st_blocks in stat result (see #722)

Fixes¶

fixed handling of O_TMPFILE in os.open (caused handling of O_DIRECTORY as O_TMPFILE) (see #723)
fixed handling of read permissions (see #719)

Version 4.7.0 (2022-09-18)¶

Changed handling of nested fixtures and bug fixes.

Changes¶

fs fixtures cannot be nested; any nested fs fixture (for example inside an fs_session or fs_module fixture) will just reference the outer fixture (the behavior had been unexpected before)

Fixes¶

reverted a performance optimization introduced in version 3.3.0 that caused hanging tests with installed torch (see #693)
do not use the built-in opener in pathlib as it may cause problems (see #697)
add support for path-like objects in shutil.disk_usage (see #699)
do not advertise support for Python 3.6 in setup.py (see #707)
return the expected type from fcntl.ioctl and fcntl.fcntl calls if arg is of type byte; the call itself does nothing as before
do not skip filesystem modules by name to allow using own modules with the same name (see #707)
add missing support for os.renames (see #714)

Version 4.6.3 (2022-07-20)¶

Another patch release that fixes a regression in version 4.6.

Changes¶

automatically reset filesystem on changing is_windows_fs or is_macos (see #692) - ensures better upwards compatibility in most cases

:warning: Make sure you write to the filesystem after you change is_windows_fs or is_macos, otherwise the changes will be lost.

Fixes¶

fixed regression: os.path.exists returned True for any root drive path under Windows

Version 4.6.2 (2022-07-14)¶

Patch release that fixes an error in the previous patch.

Fixes¶

fixed support for opener introduced in previous patch release (see #689)

Version 4.6.1 (2022-07-13)¶

Fixes incompatibility with Python 3.11 beta 4.

Note: Python 3.11 is only supported in the current beta 4 version, problems with later beta or rc versions are still possible. We will try to fix such problems in short order should they appear.

Fixes¶

added support for opener argument in open, which is used in tempfile in Python 3.11 since beta 4 (see #686)

Infrastructure¶

make sure tests run without pyfakefs installed as a package (see #687)

Version 4.6.0 (2022-07-12)¶

Adds support for Python 3.11, removes support for Python 3.6, changes root path behavior under Windows.

Changes¶

Python 3.6 has reached its end of life on 2021/12/23 and is no longer officially supported by pyfakefs
- os.stat_float_times has been removed in Python 3.7 and is therefore no longer supported
under Windows, the root path is now effectively C:\ instead of \; a path starting with \ points to the current drive as in the real file system (see #673)
fake pathlib.Path.owner() and pathlib.Path.group() now behave like the real methods - they look up the real user/group name for the user/group id that is associated with the fake file (see #678)

New Features¶

added some support for the upcoming Python version 3.11 (see #677)
added convenience fixtures for module- and session based fs fixtures (fs_module and fs_session)

Fixes¶

fixed an incompatibility of tmpdir (and probably other fixtures) with the module-scoped version of fs; had been introduced in pyfakefs 4.5.5 by the fix for #666 (see #684)

Version 4.5.6 (2022-03-17)¶

Fixes a regression which broke tests with older pytest versions (< 3.9).

Changes¶

minimum supported pytest version is now 3.0 (older versions do not work properly with current Python versions)

Fixes¶

only skip _pytest.pathlib in pytest versions where it is actually present (see #669)

Infrastructure¶

add tests with different pytest versions, starting with 3.0

Version 4.5.5 (2022-02-14)¶

Bugfix release, needed for compatibility with pytest 7.0.

Fixes¶

correctly handle file system space for files opened in write mode (see #660)
correctly handle reading/writing pipes via file (see #661)
disallow encoding argument on binary open() (see #664)
fixed compatibility issue with pytest 7.0.0 (see #666)

Version 4.5.4 (2022-01-12)¶

Minor bugfix release.

Fixes¶

added missing mocked functions for fake pipe (see #650)
fixed some bytes warnings (see #651)

Version 4.5.3 (2021-11-08)¶

Reverts a change in the previous release that could cause a regression.

Changes¶

os.listdir, os.scandir and pathlib.Path.listdir now return the directory list in a random order only if explicitly configured in the file system (use fs.shuffle_listdir_results = True with fs being the file system). In a future version, the default may be changed to better reflect the real filesystem behavior (see #647)

Version 4.5.2 (2021-11-07)¶

This is a bugfix release.

Changes¶

os.listdir, os.scandir and pathlib.Path.listdir now return the directory list in a random order (see #638)
the fcntl module under Unix is now mocked, e.g. all functions have no effect (this may be changed in the future if needed, see #645)

Fixes¶

fixed handling of alternative path separator in os.path.split, os.path.splitdrive and glob.glob (see #632)
fixed handling of failed rename due to permission error (see #643)

Version 4.5.1 (2021-08-29)¶

This is a bugfix release.

Fixes¶

added handling of path-like where missing
improved handling of str/bytes paths
suppress all warnings while inspecting loaded modules (see #614)
do not import pandas and related modules if it is not patched (see #627)
handle pathlib.Path.owner() and pathlib.Path.group by returning the current user/group name (see #629)
fixed handling of use_known_patches=False (could cause an exception)
removed Python 3.5 from metadata to disable installation for that version (see #615)

Infrastructure¶

added test dependency check (see #608)
skip tests failing with ASCII locale (see #623)

Version 4.5.0 (2021-06-04)¶

Adds some support for Python 3.10 and basic type checking.

Note: This version has been yanked from PyPI as it erroneously allowed installation under Python 3.5.

New Features¶

added support for some Python 3.10 features:
- new method pathlib.Path.hardlink_to
- new newline argument in pathlib.Path.write_text
- new follow_symlinks argument in pathlib.Path.stat and pathlib.Path.chmod
- new ‘strict’ argument in os.path.realpath

Changes¶

Python 3.5 has reached its end of life in September 2020 and is no longer supported
pathlib2 is still supported, but considered to have the same functionality as pathlib and is no longer tested separately; the previous behavior broke newer pathlib features if pathlib2 was installed (see #592)

Fixes¶

correctly handle byte paths in os.path.exists (see #595)
Update fake_pathlib to support changes coming in Python 3.10 (see
correctly handle UNC paths in os.path.split and in directory path evaluation (see #606)

Infrastructure¶

added mypy checks in CI (see #599)

Version 4.4.0 (2021-02-24)¶

Adds better support for Python 3.8 / 3.9.

New Features¶

added support for pathlib.Path.link_to (new in Python 3.8) (see #580)
added support for pathlib.Path.readlink (new in Python 3.9) (see #584)
added FakeFilesystem.create_link convenience method which creates intermittent directories (see #580)

Fixes¶

fixed handling of pipe descriptors in the fake filesystem (see #581)
added non-functional argument effective_ids to os.access (see #585)
correctly handle os.file for unreadable files (see #588)

Infrastructure¶

added automatic documentation build and check-in

Version 4.3.3 (2020-12-20)¶

Another bugfix release.

Fixes¶

Reverted one Windows-specific optimization that can break tests under some conditions (see #573)
Setting os did not reset os.sep and related variables, fixed null device name, added os.pathsep and missing os.path variables (see #572)

Version 4.3.2 (2020-11-26)¶

This is a bugfix release that fixes a regression introduced in version 4.2.0.

Fixes¶

open calls had not been patched for modules with a name ending with “io” (see #569)

Version 4.3.1 (2020-11-23)¶

This is an update to the performance release, with more setup caching and the possibility to disable it.

Changes¶

Added caching of patched modules to avoid lookup overhead
Added use_cache option and clear_cache method to be able to deal with unwanted side effects of the newly introduced caching

Infrastructure¶

Moved CI builds to GitHub Actions for performance reasons

This is mostly a performance release. The performance of the pyfakefs setup has been decreasing sufficiently, especially with the 4.x releases. This release corrects that by making the most expansive feature optional, and by adding some other performance improvements. This shall decrease the setup time by about a factor of 20, and it shall now be comparable to the performance of the 3.4 release.

Changes¶

The patchfs decorator now expects a positional argument instead of the keyword arguments fs. This avoids confusion with the pytest fs fixture and conforms to the behavior of mock.patch. You may have to adapt the argument order if you use the patchfs and mock.patch decorators together (see #566)
Default arguments that are file system functions are now not patched by default to avoid a large performance impact. An additional parameter patch_default_args has been added that switches this behavior on (see #567).

Performance¶

Added performance improvements in the test setup, including caching the unpatched modules

Version 4.2.1 (2020-11-02)¶

This is a bugfix release that fixes a regression issue.

Fixes¶

remove dependency of pyfakefs on pytest (regression, see #565)

Version 4.2.0 (2020-11-01)¶

New Features¶

add support for the buffering parameter in open (see #549)
add possibility to patch io.open_code using the new argument patch_open_code (since Python 3.8) (see #554)
add possibility to set file system OS via FakeFilesystem.os

Fixes¶

fix check for link in os.walk (see #559)
fix handling of real files in combination with home if simulating Posix under Windows (see #558)
do not call fake open if called from skipped module (see #552)
do not call fake pathlib.Path if called from skipped module (see #553)
fixed handling of additional_skip_names with several module components
allow to open existing pipe file descriptor (see #493)
do not truncate file on failed flush (see #548)
suppress deprecation warnings while collecting modules (see #542)
add support for os.truncate and os.ftruncate (see #545)

Infrastructure¶

fixed another problem with CI test scripts not always propagating errors
make sure pytest will work without pyfakefs installed (see #550)

Version 4.1.0 (2020-07-12)¶

New Features¶

Added some support for pandas (read_csv, read_excel and more), and for django file locks to work with the fake filesystem (see #531)

Fixes¶

os.expanduser now works with a bytes path
Do not override global warnings setting in Deprecator (see #526)
Make sure filesystem modules in pathlib are patched (see #527)
Make sure that alternative path separators are correctly handled under Windows (see #530)

Infrastructure¶

Make sure all temporary files from real fs tests are removed

Version 4.0.2 (2020-03-04)¶

This as a patch release that only builds for Python 3. Note that versions 4.0.0 and 4.0.1 will be removed from PyPI to disable installing them under Python 2.

Fixes¶

Do not build for Python 2 (see #524)

Version 4.0.1 (2020-03-03)¶

This as a bug fix release for a regression bug.

Note: This version has been yanked from PyPI as it erroneously allowed installation under Python 2. This has been fixed in version 4.0.2.

Fixes¶

Avoid exception if using flask-restx (see #523)

Version 4.0.0 (2020-03-03)¶

pyfakefs 4.0.0 drops support for Python 2.7. If you still need Python 2.7, you can continue to use pyfakefs 3.7.x.

Note: This version has been yanked from PyPI as it erroneously allowed installation under Python 2. This has been fixed in version 4.0.2.

Changes¶

Removed Python 2.7 and 3.4 support (see #492)

New Features¶

Added support for handling keyword-only arguments in some os functions
Added possibility to pass additional parameters to fs pytest fixture
Added automatic patching of default arguments that are file system functions
Added convenience decorator patchfs to patch single functions using the fake filesystem

Fixes¶

Added missing st_ino in makedir (see #515)
Fixed handling of relative paths in lresolve / os.lstat (see #516)
Fixed handling of byte string paths (see #517)
Fixed os.walk if path ends with path separator (see #512)
Fixed handling of empty path in os.makedirs (see #510)
Fixed handling of os.TMPFILE flag under Linux (see #509 and #511)
Adapted fake pathlib to changes in Python 3.7.6/3.8.1 (see #508)
Fixed behavior of os.makedirs in write-protected directory (see #507)

Version 3.7.2 (2020-03-02)¶

This version backports some fixes from main.

Fixes¶

Fixed handling of relative paths in lresolve / os.lstat (see #516)
Fixed os.walk if path ends with path separator (see #512)
Fixed handling of empty path in os.makedirs (see #510)
Fixed handling of os.TMPFILE flag under Linux (see #509 and #511)
Fixed behavior of os.makedirs in write-protected directory (see #507)

Version 3.7.1 (2020-02-14)¶

This version adds support for Python 3.7.6 and 3.8.1.

Fixes¶

Adapted fake pathlib to changes in Python 3.7.6/3.8.1 (see #508) (backported from main)

Version 3.7 (2019-11-23)¶

This version adds support for Python 3.8.

Note: This is the last pyfakefs version that will support Python 2.7 and Python 3.4 (possible bug fix releases notwithstanding).

New Features¶

added support for Python 3.8 (see #504)
added preliminary support for Windows-specific os.stat_result attributes tst_file_attributes and st_reparse_tag (see #504)
added support for fake os.sendfile (Posix only, Python 3 only) (see #504)

Fixes¶

support devnull in Windows under Python 3.8 (see #504)
fixed side effect of calling DirEntry.stat() under Windows (changed st_nlink) (see #502)
fixed problem of fake modules still referenced after a test in modules loaded during the test (see #501 and #427)
correctly handle missing read permission for parent directory (see #496)
raise for os.scandir with non-existing directory (see #498)

Infrastructure¶

fixed CI tests scripts to always propagate errors (see #500)

Version 3.6.1 (2019-10-07)¶

Fixes¶

avoid rare side effect during module iteration in test setup (see #338)
make sure real OS tests are not executed by default (see #495)

Version 3.6 (2019-06-30)¶

Changes¶

removed unneeded parameter use_dynamic_patch

New Features¶

support for src_dir_fd and dst_dir_fd arguments in os.rename, os.replace and os.link
added possibility to use modules instead of module names for the additional_skip_names argument (see #482)
added argument allow_root_user to Patcher and UnitTest to allow forcing non-root access (see #474)
added basic support for os.pipe (see #473)
added support for symlinks in add_real_directory
added new public method add_real_symlink

Infrastructure¶

added check for correctly installed Python 3 version in Travis.CI (see #487)

Fixes¶

fixed incorrect argument names for some os functions
fake DirEntry now implements os.PathLike in Python >= 3.6 (see #483)
fixed incorrect argument name for os.makedirs (see #481)
avoid pytest warning under Python 2.7 (see #466)
add next to FakeFileWrapper (see #485)

Version 3.5.8 (2019-06-21)¶

Another bug-fix release that mainly fixes a regression with Python 2 that has been introduced in version 3.5.3.

Fixes¶

regression: patching built-in open under Python 2 broke unit tests (see #469)
fixed writing to file added with add_real_file (see #470)
fixed argument name of FakeIOModule.open (see #471)

Infrastructure¶

more changes to run tests using python setup.py test under Python 2 regardless of pathlib2 presence

Version 3.5.7 (2019-02-08)¶

This is mostly a bug-fix release.

Fixes¶

regression: pathlib did not get patched in the presence of pathlib2 (see #467)
fixed errors if running the PyCharm debugger under Python 2 (see #464)

Infrastructure¶

do not run real file system tests by default (fixes deployment problem, see #465)
make tests run if running python setup.py test under Python 2

Version 3.5.6 (2019-01-13)¶

Changes¶

import external pathlib2 and scandir packages first if present (see #462)

Version 3.5.5 (2018-12-20)¶

Fixes¶

removed shebang from test files to avoid packaging warnings (see #461)

Version 3.5.4 (2018-12-19)¶

New Features¶

added context manager class Pause for pause/resume (see #448)

Fixes¶

fixed AttributeError shown while displaying fs in a failing pytest in Python 2
fixed permission handling for root user
avoid AttributeError triggered by modules without __module__ attribute (see #460)

Version 3.5.3 (2018-11-22)¶

This is a minor release to have a version with passing tests for OpenSUSE packaging.

New Features¶

automatically patch file system methods imported as another name like from os.path import exists as my_exists, including builtin open and io.open

Fixes¶

make tests for access time less strict to account for file systems that do not change it immediately (#453)

Version 3.5.2 (2018-11-11)¶

This is mostly a bug-fix release.

New Features¶

added support for pause/resume of patching the file system modules (#448)
allow to set current group ID, set current user ID and group ID as st_uid and st_gid in new files (#449)

Fixes¶

fixed using modules_to_patch (regression, see #450)
fixed recursion error on unpickling the fake file system (#445)
allow trailing path in add_real_directory (#446)

Version 3.5 (2018-10-22)¶

Changes¶

This version of pyfakefs does not support Python 3.3. Python 3.3 users must keep using pyfakefs 3.4.3, or upgrade to a newer Python version.
The deprecation warnings for the old API are now switched on by default. To switch them off for legacy code, use:
```
from pyfakefs.deprecator import Deprecator

Deprecator.show_warnings = False
```

New Features¶

Improved automatic patching:
- automatically patch methods of a patched file system module imported like from os.path import exists (#443)
- a module imported as another name (import os as _os) is now correctly patched without the need of additional parameters (#434)
- automatically patch Path if imported like from pathlib import Path (#440)
- parameter patch_path has been removed from UnitTest and Patcher, the correct patching of path imports is now done automatically (#429)
- UnitTest /Patcher arguments can now also be set in setUpPyfakefs() (#430)
added possibility to set user ID (#431)
added side_effect option to fake files (#433)
added some support for extended filesystem attributes under Linux (#423)
handle contents=None in create_file() as empty contents if size not set (#424)
added pathlib2 support (#408) (#422)
added support for null device (#418)
improved error message for “Bad file descriptor in fake filesystem” (#419)

Fixes¶

fixed pytest when both pyfakefs and future are installed (#441)
file timestamps are now updated more according to the real behavior (#435)
fixed a problem related to patching shutil functions using zipfile (#427)

Version 3.4.3 (2018-06-13)¶

This is mostly a bug fix release, mainly for bugs found by @agroce using tstl.

New Features¶

added support for path-like objects as arguments in create_file(), create_dir(), create_symlink(), add_real_file() and add_real_directory() (Python >= 3.6, see #409)

Infrastructure¶

moved tests into package
use README.md in pypi (#358)

Fixes¶

tell after seek gave incorrect result in append mode (#363)
a failing pytest did not display the test function correctly (#381)
flushing file contents after truncate was incorrect under some conditions (#412)
readline() did not work correctly in binary mode (#411)
pathlib.Path.resolve() behaved incorrectly if the path does not exist (#401)
closed attribute was not implemented in fake file (#380)
add_real_directory did not behave correctly for nested paths
the following functions did not behave correctly for paths ending with a path separator (found by @agroce using tstl):
- os.rename (#400)
- os.link (#399, #407)
- os.rmdir (#398)
- os.mkdir, os.makedirs (#396)
- os.rename (#391, #395, #396, #389, #406)
- os.symlink (#371, #390)
- os.path.isdir (#387)
- open (#362, #369, #397)
- os.path.lexists, os.path.islink (#365, #373, #396)
- os.remove (#360, #377, #396)
- os.stat (#376)
- os.path.isfile (#374)
- os.path.getsize (#368)
- os.lstat (#366)
- os.path.exists (#364)
- os.readlink (#359, #372, #392)

Version 3.4.1 (2018-03-18)¶

This is a bug fix only release.

Fixes¶

Missing cleanup after using dynamic patcher let to incorrect behavior of tempfile after test execution (regression, see #356)
add_real_directory does not work after chdir (see #355)

Version 3.4 (2018-03-08)¶

This version of pyfakefs does not support Python 2.6. Python 2.6 users must use pyfakefs 3.3 or earlier.

New Features¶

Added possibility to map real files or directories to another path in the fake file system (see #347)
Configuration of Patcher and TestCase:
- Possibility to reload modules is now also available in Patcher
- Added possibility to add own fake modules via modules_to_patch argument (see #345)
- Dynamic loading of modules after setup is now on by default and no more considered experimental (see #340)
Added support for file descriptor path parameter in os.scandir (Python >= 3.7, Posix only) (see #346)
Added support to fake out backported scandir module (#332)
IOError/OSError exception messages in the fake file system now always start with the message issued in the real file system in Unix systems (see #202)

Infrastructure¶

Changed API to be PEP-8 conform (#186). Note: The old API is still available.
Removed Python 2.6 support (#293)
Added usage documentation to GitHub Pages
Added contributing guide
Added flake8 tests to Travis CI

Fixes¶

Links in base path in os.scandir shall not be resolved (#350)
Fixed unit tests when run on a computer not having umask set to 0022
Correctly handle newline parameter in open() for Python 3, added support for universal newline mode in Python 2 (#339)
Fixed handling of case-changing rename with symlink under MacOS (#322)
Creating a file with a path ending with path separator did not raise (#320)
Fixed more problems related to flush (#302, #300)
Correctly handle opening files more than once (#343)
Fake os.lstat() crashed with several trailing path separators (#342)
Fixed handling of path components starting with a drive letter(#337)
Symlinks to absolute paths were incorrectly resolved under Windows (#341)
Unittest mock didn’t work after setUpPyfakefs (#334)
os.path.split() and os.path.dirname() gave incorrect results under Windows (#335)

Version 3.3 (2017-11-12)¶

This is the last release that supports Python 2.6.

New Features¶

The OS specific temp directory is now automatically created in setUp() (related to #191). Note that this may break test code that assumes that the fake file system is completely empty at test start.
Added possibility to reload modules and switch on dynamic loading of modules after setup (experimental, see #248)
Added possibility to patch modules that import file system modules under another name, for example import os as '_os (#231)
Added support for dir_fd argument in several os functions (#206)
Added support for open file descriptor as path argument in os.utime, os.chmod, os.chdir, os.chown, os.listdir, os.stat and os.lstat (Python >= 3.3) (#205)
Added support for basic modes in fake os.open() (#204)
Added fake os.path.samefile implementation (#193)
Added support for ns argument in os.utime() (Python >= 3.3) (#192)
Added nanosecond time members in os.stat_result (Python >= 3.3) (#196)

Infrastructure¶

Added Travis CI tests for MacOSX (Python 2.7 and 3.6)
Added Appveyor CI tests for Windows (Python 2.7, 3.3 and 3.6)
Added auto-generated documentation for development version on GitHub Pages
Removed most of fake_filesystem_shutil implementation, relying on the patched os module instead (#194)
Removed fake_tempfile and fake_filesystem_glob, relying on the patched os module instead (#189, #191)

Fixes¶

Multiple fixes of bugs found using TSTL by @agroce (see about 100 issues with the TSTL label)
- several problems with buffer handling in high-level IO functions
- several problems with multiple handles on the same file
- several problems with low-level IO functions
- incorrect exception (IOError vs OSError) raised in several cases
- Fake rename did not behave like os.rename in many cases
- Symlinks have not been considered or incorrectly handled in several functions
- A nonexistent file that has the same name as the content of the parent object was seen as existing
- Incorrect error handling during directory creation
- many fixes for OS-specific behavior
Also patch modules that are loaded between __init__() and setUp() (#199)
Creating files in read-only directory was possible (#203)

Version 3.2 (2017-05-27)¶

New Features¶

The errors argument is supported for io.open() and os.open()
New methods add_real_file(), add_real_directory() and add_real_paths() make real files and directories appear within the fake file system. File contents are read from the real file system only as needed (#170). See example_test.py for a usage example.
Deprecated TestCase.copyRealFile() in favor of add_real_file(). copyRealFile() remains only for backward compatibility. Also, some less-popular argument combinations have been disallowed.
Added this file you are reading, CHANGES.md, to the release manifest

Infrastructure¶

The mox3 package is no longer a prerequisite–the portion required by pyfakefs has been integrated into pyfakefs (#182)

Fixes¶

Corrected the handling of byte/unicode paths in several functions (#187)
FakeShutilModule.rmtree() failed for directories ending with path separator (#177)
Case was incorrectly handled for added Windows drives
pathlib.glob() incorrectly handled case under MacOS (#167)
tox support was broken (#163)
On Windows it was not possible to rename a file when only the case of the file name changed (#160)

Version 3.1 (2017-02-11)¶

New Features¶

Added helper method TestCase.copyRealFile() to copy a file from the real file system to the fake file system. This makes it easy to use template, data and configuration files in your tests.
A pytest plugin is now installed with pyfakefs that exports the fake filesystem as pytest fixture fs.

Fixes¶

Incorrect disk usage calculation if too large file created (#155)

Version 3.0 (2017-01-18)¶

New Features¶

Support for path-like objects as arguments in fake os and os.path modules (Python >= 3.6)
Some changes to make pyfakefs work with Python 3.6
Added fake pathlib module (Python >= 3.4) (#29)
Support for os.replace (Python >= 3.3)
os.access, os.chmod, os.chown, os.stat, os.utime: support for follow_symlinks argument (Python >= 3.3)
Support for os.scandir (Python >= 3.5) (#119)
Option to not fake modules named path (#53)
glob.glob, glob.iglob: support for recursive argument (Python >= 3.5) (#116)
Support for glob.iglob (#59)

Infrastructure¶

Added auto-generated documentation

Fixes¶

shutil.move incorrectly moves directories (#145)
Missing support for ‘x’ mode in open (Python >= 3.3) (#147)
Incorrect exception type in Posix if path ancestor is a file (#139)
Exception handling when using Patcher with py.test (#135)
Fake os.listdir returned sorted instead of unsorted entries

Version 2.9 (2016-10-02)¶

New Features¶

io.open, os.open: support for encoding argument (#120)
os.makedirs: support for exist_ok argument (Python >= 3.2) (#98)
Support for fake io.open() (#70)
Support for mount points (#25)
Support for hard links (#75)
Support for float times (mtime, ctime)
Windows support:
- support for alternative path separator
- support for case-insensitive filesystems (#69)
- support for drive letters and UNC paths
Support for filesystem size (#86)
shutil.rmtree: support for ignore_errors and onerror arguments (#72)
Support for os.fsync() and os.fdatasync() (#73)
os.walk: Support for followlinks argument

Fixes¶

shutil functions like make_archive do not work with pyfakefs (#104)
File permissions on deletion not correctly handled (#27)
shutil.copy error with bytes contents (#105)
mtime and ctime not updated on content changes

Version 2.7 ¶

Infrastructure¶

Moved repository from GoogleCode to GitHub, merging 3 projects
Added continuous integration testing with Travis CI
Added usage documentation in project wiki
Better support for pypi releases

New Features¶

Added direct unit test support in fake_filesystem_unittest (transparently patches all calls to faked implementations)
Added support for doctests
Added support for cygwin
Better support for Python 3

Fixes¶

os.utime fails to traverse symlinks (#49)
chown incorrectly accepts non-integer uid/gid arguments (#30)
Reading from fake block devices doesn’t work (#24)
fake_tempfile is using AddOpenFile incorrectly (#23)
Incorrect behavior of relpath, abspath and normpath on Windows.
Cygwin wasn’t treated as Windows (#37)
Python 3 open in binary mode not working (#32)
os.remove doesn’t work with relative paths (#31)
mkstemp returns no valid file descriptor (#19)
open methods lack IOError for prohibited operations (#18)
Incorrectly resolved relative path (#3)
FakeFileOpen keyword args do not match the __builtin__ equivalents (#5)
Relative paths not supported (#16, #17))

Older Versions¶

There are no release notes for releases 2.6 and below. The following versions are still available on PyPI:

1.1, 1.2, 2.0, 2.1, 2.2, 2.3 and 2.4