python: Add pipenv support

pipenv is a tool used for managing virtual environments with pinned,
explicit dependencies. It is used for precisely recreating python
virtual environments.

pipenv uses two files to do this:

(1) Pipfile, which is similar in purpose and scope to what setup.cfg
lists. It specifies the requisite minimum to get a functional
environment for using this package.

(2) Pipfile.lock, which is similar in purpose to `pip freeze >
requirements.txt`. It specifies a canonical virtual environment used for
deployment or testing. This ensures that all users have repeatable
results.

The primary benefit of using this tool is to ensure *rock solid*
repeatable CI results with a known set of packages. Although I endeavor
to support as many versions as I can, the fluid nature of the Python
toolchain often means tailoring code for fairly specific versions.

Note that pipenv is *not* required to install or use this module; this is
purely for the sake of repeatable testing by CI or developers.

Here, a "blank" pipfile is added with no dependencies, but specifies
Python 3.6 for the virtual environment.

Pipfile will specify our version minimums, while Pipfile.lock specifies
an exact loadout of packages that were known to operate correctly. This
latter file provides the real value for easy setup of container images
and CI environments.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Cleber Rosa <crosa@redhat.com>
Message-id: 20210527211715.394144-15-jsnow@redhat.com
Signed-off-by: John Snow <jsnow@redhat.com>

python/Pipfile

@@ -0,0 +1,11 @@
+[[source]]
+name = "pypi"
+url = "https://pypi.org/simple"
+verify_ssl = true
+
+[dev-packages]
+
+[packages]
+
+[requires]
+python_version = "3.6"

python/README.rst

@@ -36,6 +36,9 @@ Files in this directory
 - ``MANIFEST.in`` is read by python setuptools, it specifies additional files
   that should be included by a source distribution.
 - ``PACKAGE.rst`` is used as the README file that is visible on PyPI.org.
+- ``Pipfile`` is used by Pipenv to generate ``Pipfile.lock``.
+- ``Pipfile.lock`` is a set of pinned package dependencies that this package
+  is tested under in our CI suite. It is used by ``make venv-check``.
 - ``README.rst`` you are here!
 - ``VERSION`` contains the PEP-440 compliant version used to describe
   this package; it is referenced by ``setup.cfg``.