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pyfakefs implements a fake file system that mocks the Python file system modules.

Project description

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.

The current pyfakfs API is referenced in the auto-generated documentation. A list of changes in the latest versions can be found in the Release Notes.


There are two approaches to implementing tests using pyfakefs.

The first method is to allow pyfakefs to automatically find all real file functions and modules, and stub these out with the fake file system functions and modules. This is explained in the usage tutorial and demonstrated by and

The other approach is to do the patching yourself using mock.patch():

import pyfakefs.fake_filesystem as fake_fs

# Create a faked file system
fs = fake_fs.FakeFilesystem()

# Do some setup on the faked file system

# Replace some built-in file system related modules you use with faked ones

# Assuming you are using the mock library to ... mock things
    from unittest.mock import patch  # In Python 3, mock is built-in
except ImportError:
    from mock import patch  # Python 2

import pyfakefs.fake_filesystem_glob as fake_glob

# Note that this fake module is based on the fake fs you just created
glob = fake_glob.FakeGlobModule(fs)
with patch('mymodule.glob', glob):

Usage as a Pytest Plugin

Installation of pyfakefs also provides a PyTest plugin. The plugin makes the fs fixture available for any test. For example:

def my_fakefs_test(fs):
    # "fs" is the reference to the fake file system
    assert os.path.exists('/var/data/xx1.txt')

Similar to the unittest class (fake_filesystem_unittest.TestCase), the fs fixture stubs out all file system functions and modules.

Continuous Integration

pyfakefs is automatically tested with Python 2.6 and above, and it is currently Build Status.

See Travis-CI for test results for each Python version.



pyfakefs works with Python 2.6 and above, on Linux, Windows and OSX (MacOS).

pyfakefs requires mox3.

pyfakefs works with PyTest version 2.8.6 or above.

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 Google alone, pyfakefs is used in over 2,000 Python tests.

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

Fork jmcgeheeiv-pyfakefs added a usage tutorial, 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 maintains and extends pyfakefs.

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