pyfakefs

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 creates a new empty in-memory file system at each test start, which replaces the real filesystem during the test. Think of pyfakefs as making a per-test temporary directory, except for an entire file system.

pyfakefs is tested with current versions of Linux, Windows and macOS.

Usage

There are several ways to invoke pyfakefs:

using the fs fixture with pytest
deriving from fake_filesystem_unittest.TestCase for unittest
using fake_filesystem_unittest.Patcher as context manager
using the fake_filesystem_unittest.patchfs decorator on a single test

Refer to the usage documentation for more information.

Documentation

Release documentation covers the latest released version
Development documentation for the current main branch
Release Notes
Contributing Guide - contributions are welcome!

Features

Apart from automatically mocking most file-system functions, pyfakefs provides some additional features:

mapping files and directories from the real file system into the fake filesystem
configuration and tracking of the file system size
pause and resume of patching to be able to use the real file system inside a test step
(limited) emulation of other OSes (Linux, macOS or Windows)
configuration to behave as if running as a non-root user while running under root

Limitations

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. Refer to the documentation for more information about the limitations of pyfakefs.

History

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. At last count, pyfakefs was used in over 20,000 Python tests at Google.

Google released pyfakefs to the public in 2011 as a Google Code project. Support for unittest and doctest was added in a fork by user jmcgeheeiv, further corrections were made in a separate fork with user shiffdane, and after the shutdown of Google Code was announced, John McGehee merged all three Google Code projects together here on GitHub. In 2022, the repository has been transferred to pytest-dev to ensure continuous maintenance.

Metadata

Release files for pyfakefs 6.2.0

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Source distribution (sdist)

Source distribution for pyfakefs 6.2.0
File	Size	Uploaded
pyfakefs-6.2.0.tar.gz	228.3 kB	Apr 12, 2026	Details

Built distribution (wheel)

Table of built distributions (wheels) for pyfakefs 6.2.0
File	Interpreter	ABI	Platform	Reset
pyfakefs-6.2.0-py3-none-any.whl 241.1 kB Apr 12, 2026	Python 3	none	any	Details

Total release size: 469.4 kB

Release files / pyfakefs-6.2.0.tar.gz

Download URL	pyfakefs-6.2.0.tar.gz
Size	228.3 kB
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SHA-256 checksum How to use checksums	`e59a36db447bf509ce9c97ab3d1510c08cc51895c5311325a560a5e5b5dc1940`
BLAKE2b-256 checksum How to use checksums	`980dc80012ee6e885c293ad63c5f5b049d3ef3fd2b32bbe6fa8739145f392ec6`
Upload date	Apr 12, 2026
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Publishing repository: github.com/pytest-dev/pyfakefs
Publishing commit: github.com/pytest-dev/pyfakefs/tree/b3be3a3ed57b156839435408ea0fe5aede0109ed

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Publishing configuration: github.com/pytest-dev/pyfakefs/blob/b3be3a3ed57b156839435408ea0fe5aede0109ed/.github/workflows/release-deploy.yml
Publishing logs: github.com/pytest-dev/pyfakefs/actions/runs/24308011737/attempts/1

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SHA-256 checksum: e59a36db447bf509ce9c97ab3d1510c08cc51895c5311325a560a5e5b5dc1940 Verifying attestations

Release files / pyfakefs-6.2.0-py3-none-any.whl

Download URL	pyfakefs-6.2.0-py3-none-any.whl
Size	241.1 kB
Tags	Python 3
SHA-256 checksum How to use checksums	`0968a49db692694ffed420e54a9f1cbae4636637b880e8ab09c8ccc0f11bd7ae`
BLAKE2b-256 checksum How to use checksums	`b28097571ac8295289c267367b7b60aadeae1a9a841e83f0a96ad9b65d1dd3c0`
Upload date	Apr 12, 2026
Uploaded using Trusted Publishing? What is trusted publishing?	Yes
Uploaded via	`twine/6.1.0 CPython/3.13.12`

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Identity

Publishing platform: GitHub Actions
Publishing repository: github.com/pytest-dev/pyfakefs
Publishing commit: github.com/pytest-dev/pyfakefs/tree/b3be3a3ed57b156839435408ea0fe5aede0109ed

Workflow

Publishing configuration: github.com/pytest-dev/pyfakefs/blob/b3be3a3ed57b156839435408ea0fe5aede0109ed/.github/workflows/release-deploy.yml
Publishing logs: github.com/pytest-dev/pyfakefs/actions/runs/24308011737/attempts/1

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Subject: pyfakefs-6.2.0-py3-none-any.whl
SHA-256 checksum: 0968a49db692694ffed420e54a9f1cbae4636637b880e8ab09c8ccc0f11bd7ae Verifying attestations