For details on this feature, see:
https://setuptools.readthedocs.io/en/latest/setuptools.html#configuring-setup-using-setup-cfg-files

Setuptools allows using setup.cfg as a configuration file to define the
package metadata and options. This approach reduces boilerplate code in
favor of a declarative configuration. Down the road, this approach also
allows for automation through scripts and tools.

Python 3.4 has been EOL since 2019-03-18.

Removing from the test matrix helps reduce testing resources.

For additional details on unsupported Python versions, see:

https://devguide.python.org/devcycle/#end-of-life-branches

tox can now always be used as the test entry point and allows for
contributors to easily test the full test matrix locally.

Starting with setuptools v41.5.0 (27 Oct 2019) the `setup.py test`
command is formally deprecated. It now emits a warning on use. Prior to
this version, it use was discouraged by the setuptools developers.

Now, always use tox as the one testing entry point. It handles multiple
version of Python and Redis.

The Travis CI configuration was reworked to use tox to install
dependencies and run tests in the same manner that contributors would do
locally.

Modern Python environments have setuptools or pip installed. The
distutils fallback is unnecessary.

Allows using Python version 3.7 without sudo declarations.

Travis officially added support for Xenial on 2018-11-08.

https://blog.travis-ci.com/2018-11-08-xenial-release

Add Python 3.7 to tox.ini and setup.py as well.

Now that redis-py has removed support for EOL Pythons, can once again
run tests using the latest version of pytest.

Helps pip decide what version of the library to install.

https://packaging.python.org/tutorials/distributing-packages/#python-requires

> If your project only runs on certain Python versions, setting the
> python_requires argument to the appropriate PEP 440 version specifier
> string will prevent pip from installing the project on other Python
> versions.

https://setuptools.readthedocs.io/en/latest/setuptools.html#new-and-changed-setup-keywords

> python_requires
>
> A string corresponding to a version specifier (as defined in PEP 440)
> for the Python version, used to specify the Requires-Python defined in
> PEP 345.

Python 3.3 is EOL. It is no longer receiving bug fixes, including for
security issues. It has been EOL since 2017-09-29. For additional
details of the status of Python versions, see:

https://devguide.python.org/#status-of-python-branches