pyfakefs
Implements a fake file system that mocks the Python file system modules.
Decision gist · record as of 2026-08-14
Yes. pyfakefs is production-stable (Development Status 5), actively maintained, has no security vulnerabilities, and zero runtime dependencies. It solves a real testing problem—isolating filesystem operations—and is widely used. Install it if your test suite touches the filesystem.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.10 or later; C-based filesystem libraries cannot be mocked by pyfakefs.
- Low friction: pure Python wheel with no runtime dependencies.
- Actively maintained with recent releases; last commit 2026-08-13.
License · maintenance · safety
Apache-2.0 (permissive) — Apache-2.0 (permissive): you can use, modify, and distribute pyfakefs freely in commercial and private projects, provided you include a copy of the license and state significant changes.
last release 2026-04-12 (124 days) · last repo commit 2026-08-13 · 750 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 4,466,529 downloads/mo, #2,298 on PyPI
Alternatives
Verify before relying
pip install pyfakefs
from pyfakefs import fake_filesystem_unittest
class TestWithFakeFS(fake_filesystem_unittest.TestCase):
def setUp(self):
self.setUpPyfakefs()
def test_file_operations(self):
self.fs.create_file('/tmp/test.txt', contents='hello')
with open('/tmp/test.txt') as f:
self.assertEqual(f.read(), 'hello')- Performance characteristics when filesystem size grows or test count scales
- Compatibility with specific C-based libraries beyond the documented limitations
- Whether all test frameworks and plugins work seamlessly with pyfakefs patching
What it is and what it does
pyfakefs is a testing library that replaces the real filesystem with an in-memory fake one during test execution. It automatically mocks Python's file system modules so your tests can create, read, and manipulate files without touching disk. Each test gets a fresh empty filesystem, making tests isolated and fast. The library works with unittest (via TestCase subclass or Patcher context manager) and as a decorator on individual tests.
The package handles cross-platform testing by emulating Linux, Windows, and macOS filesystems, and includes features like mapping real files into the fake filesystem, tracking filesystem size, pausing/resuming patching, and simulating non-root user behavior. It does not work with libraries that use C-level filesystem access, since pyfakefs cannot patch underlying C library calls.
Use it for
- Test file I/O code (reading, writing, deleting) without creating temporary files on disk
- Verify error handling for missing files or permission issues in a controlled environment
- Run filesystem-heavy test suites in parallel without disk contention or cleanup overhead
- Test cross-platform file path logic (Windows vs. POSIX) on a single machine
- Simulate full filesystem scenarios (large directory trees, disk full conditions) cheaply in memory
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes.
pyfakefs is production-stable (Development Status 5), actively maintained, has no security vulnerabilities, and zero runtime dependencies. It solves a real testing problem—isolating filesystem operations—and is widely used. Install it if your test suite touches the filesystem.
Install
pyfakefs on PyPI
Before you install
Low friction: pure Python wheel with no runtime dependencies. Actively maintained with recent releases; last commit 2026-08-13. Supports current Python versions on Linux, Windows, and macOS.
Requires Python 3.10 or later; C-based filesystem libraries cannot be mocked by pyfakefs.
License in practice
Apache-2.0 (permissive): you can use, modify, and distribute pyfakefs freely in commercial and private projects, provided you include a copy of the license and state significant changes.
Quickstart
pip install pyfakefs
from pyfakefs import fake_filesystem_unittest
class TestWithFakeFS(fake_filesystem_unittest.TestCase):
def setUp(self):
self.setUpPyfakefs()
def test_file_operations(self):
self.fs.create_file('/tmp/test.txt', contents='hello')
with open('/tmp/test.txt') as f:
self.assertEqual(f.read(), 'hello')Verify before relying
- Performance characteristics when filesystem size grows or test count scales
- Compatibility with specific C-based libraries beyond the documented limitations
- Whether all test frameworks and plugins work seamlessly with pyfakefs patching
Package facts
| License | Apache-2.0 permissive |
| Python support | Supports the current Python release >=3.10 |
| Install friction | Low. Pure-Python wheel |
| Runtime dependencies | None |
| Maintenance | Actively maintained 124 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 4,466,529 / month, #2,298 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Development Status :: 5 - Production/StableEnvironment :: ConsoleFramework :: PytestIntended Audience :: DevelopersOperating System :: MacOSOperating System :: Microsoft :: WindowsOperating System :: POSIXProgramming Language :: Python :: 3Programming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.14Programming Language :: Python :: Implementation :: CPythonProgramming Language :: Python :: Implementation :: PyPyTopic :: Software Development :: LibrariesTopic :: Software Development :: Libraries :: Python ModulesTopic :: Software Development :: TestingTopic :: System :: Filesystems |
Evidence: pyfakefs-6.2.0-py3-none-any.whl
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