contextlib2 is a backport of the standard library's contextlib module to earlier Python versions.

It also sometimes serves as a real world proving ground for possible future enhancements to the standard library version.

Licensing

As a backport of Python standard library software, the implementation, test suite and other supporting files for this project are distributed under the Python Software License used for the CPython reference implementation.

The one exception is the included type hints file, which comes from the typeshed project, and is hence distributed under the Apache License 2.0.

Development

contextlib2 has no runtime dependencies, but requires setuptools and wheel at build time to generate universal wheel archives.

Local testing is a matter of running:

python3 -m unittest discover -t . -s test

You can test against multiple versions of Python with tox:

pip install tox
tox

Versions currently tested in both tox and GitHub Actions are:

• CPython 3.8
• CPython 3.9
• CPython 3.10
• CPython 3.11
• CPython 3.12
• PyPy3 (specifically 3.10 in GitHub Actions)

Updating to a new stdlib reference version

As of Python 3.12.3, 4 files needed to be copied from the CPython reference implementation to contextlib2:

• Doc/library/contextlib.rst -> docs/contextlib2.rst
• Lib/contextlib.py -> contextlib2/__init__.py
• Lib/test/test_contextlib.py -> test/test_contextlib.py
• Lib/test/test_contextlib_async.py -> test/test_contextlib_async.py

The corresponding version of contextlib2/__init__.pyi also needs to be retrieved from the typeshed project:

wget https://raw.githubusercontent.com/python/typeshed/master/stdlib/contextlib.pyi

The following patch files are saved in the dev directory:

• changes to contextlib2/__init__.py to get it to run on the older versions (and to add back in the deprecated APIs that never graduated to the standard library version)
• changes to test/test_contextlib.py and test/test_contextlib_async.py to get them to run on the older versions
• changes to contextlib2/__init__.pyi to make the Python version guards unconditional (since the contextlib2 API is the same on all supported versions)
• changes to docs/contextlib2.rst to use contextlib2 version numbers in the version added/changed notes and to integrate the module documentation with the rest of the project documentation

When the upstream changes between releases are minor, these patch files may be used directly to reapply the contextlib2 specific changes after syncing a new version. Even when the patches do not apply cleanly, they're still a useful guide as to the changes that are needed to restore compatibility with older Python versions and make any other contextlib2 specific updates.

The test directory is laid out so that the test suite's imports from test.support work the same way as they do in the main CPython test suite. These files are selective copies rather than complete ones as the contextlib tests only need a tiny fraction of the features available in the real test.support module.

The dev/sync_from_cpython.sh and dev/save_diff_snapshot.sh scripts automate some of the steps in the sync process.