You can not select more than 25 topics Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
mrbean-bremen 84b13e16d9
Add notes to usage documentation
56 minutes ago
.github Automatically reset filesystem on changing os 4 weeks ago
docs Add notes to usage documentation 56 minutes ago
pyfakefs Add support for path-like objects in shutil.disk_usage 6 days ago
.gitignore Add option to switch off cache 2 years ago Add notes to usage documentation 56 minutes ago Minor documentation changes 2 years ago
COPYING Add license statement to to resolve #50. 7 years ago
Dockerfile Test using dockerfiles with different OSes 3 years ago Directly use for pypi (use new pypi feature) 4 years ago Add some support for Python 3.11 2 months ago
extra_requirements.txt Update openpyxl from 3.0.9 to 3.0.10 3 months ago
mypy.ini Add type checking (#601) 1 year ago
requirements.txt Add fs_module to for plugin tests 1 month ago
setup.cfg setup.cfg: Replace dashes with underscores 10 months ago Add some support for Python 3.11 2 months ago
tox.ini Add Python 3.9 and 3.10 to tox.ini (#670) 5 months ago

pyfakefs PyPI version Python version Testsuite

pyfakefs implements a fake file system that mocks the Python file system modules. Using pyfakefs, your tests operate on a fake file system in memory without touching the real disk. The software under test requires no modification to work with pyfakefs.

pyfakefs works with Linux, Windows and MacOS.


This file provides general usage instructions for pyfakefs. There is more:

  • The documentation at GitHub Pages:
    • The Release documentation contains usage documentation for pyfakefs and a description of the most relevant classes, methods and functions for the last version released on PyPi
    • The Development documentation contains the same documentation for the current master branch
    • The Release 3.7 documentation contains usage documentation for the last version of pyfakefs supporting Python 2.7
    • The Release 3.3 documentation contains usage documentation for the last version of pyfakefs supporting Python 2.6, and for the old-style API (which is still supported but not documented in the current release)
  • The Release Notes show a list of changes in the latest versions

Linking to pyfakefs

In your own documentation, please link to pyfakefs using the canonical URL This URL always points to the most relevant top page for pyfakefs.


pyfakefs has support for unittest and pytest, but can also be used directly using fake_filesystem_unittest.Patcher. Refer to the usage documentation for more information on test scenarios, test customization and using convenience functions.


pyfakefs works with CPython 3.7 and above, on Linux, Windows and OSX (MacOS), and with PyPy3.

pyfakefs works with pytest version 3.0.0 or above.

pyfakefs will not work with Python libraries that use C libraries to access the file system. This is because pyfakefs cannot patch the underlying C libraries' file access functions--the C libraries will always access the real file system. For example, pyfakefs will not work with lxml. In this case lxml must be replaced with a pure Python alternative such as xml.etree.ElementTree.


Continuous integration

pyfakefs is currently automatically tested on Linux, MacOS and Windows, with Python 3.7 to 3.11, and with PyPy3 on Linux, using GitHub Actions.

Running pyfakefs unit tests

On the command line

pyfakefs unit tests can be run using unittest or pytest:

$ cd pyfakefs/

$ python -m pyfakefs.tests.all_tests
$ python -m pyfakefs.tests.all_tests_without_extra_packages
$ python -m pytest pyfakefs/pytest_tests/

These scripts are called by tox and Travis-CI. tox can be used to run tests locally against supported python versions:

$ tox

In a Docker container

The Dockerfile at the repository root will run the tests on the latest Ubuntu version. Build the container:

cd pyfakefs/
docker build -t pyfakefs .

Run the unit tests in the container:

docker run -t pyfakefs

Contributing to pyfakefs

We always welcome contributions to the library. Check out the Contributing Guide for more information.

History was initially developed at Google by Mike Bland as a modest fake implementation of core Python modules. It was introduced to all of Google in September 2006. Since then, it has been enhanced to extend its functionality and usefulness. At last count, pyfakefs is used in over 2,000 Python tests at Google.

Google released pyfakefs to the public in 2011 as Google Code project pyfakefs:

After the shutdown of Google Code was announced, John McGehee merged all three Google Code projects together here on GitHub where an enthusiastic community actively supports, maintains and extends pyfakefs.