pyfakefs implements a fake file system that mocks the Python file system modules.
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 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 http://pyfakefs.org. This URL always points to the most relevant top page for pyfakefs.
pyfakefs has support for
pytest, but can also be used
fake_filesystem_unittest.Patcher. Refer to the
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
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
$ cd pyfakefs/ $ export PYTHONPATH=$PWD $ python -m pyfakefs.tests.all_tests $ python -m pyfakefs.tests.all_tests_without_extra_packages $ python -m pytest pyfakefs/pytest_tests/pytest_plugin_test.py
These scripts are called by
tox and Travis-CI.
tox can be used to run tests
locally against supported python versions:
In a Docker container
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.
pyfakefs.py 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:
- Fork jmcgeheeiv-pyfakefs added direct support for unittest and doctest
- Fork shiffdane-jmcgeheeiv-pyfakefs added further corrections
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.
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