ydb/contrib/python/contextlib2/py3

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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 3.6
* CPython 3.7
* CPython 3.8
* CPython 3.9
* CPython 3.10
* PyPy3

Updating to a new stdlib reference version
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

As of Python 3.10, 4 files needed to be copied from the CPython reference
implementation to contextlib2:

* ``Doc/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

For the 3.10 sync, the only changes needed to the test files were to import from
``contextlib2`` rather than ``contextlib``. The test directory is laid out so
that the test suite's imports from ``test.support`` work the same way they do in
the main CPython test suite.

The following patch files are saved in the ``dev`` directory:

* changes made 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 made to ``contextlib2/__init__.pyi`` to make the Python version
guards unconditional (since the ``contextlib2`` API is the same on all
supported versions)
* changes made 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