Declare supported Python versions in setup.{py,cfg}

[Freso]

Right now Python support is only checked for using custom code in setup.py (the if sys.version_info[0:2] < (3, 5): clause). This causes some issues with downstream users as Python 2.7 and 3.5 were dropped with 1.1.x and just asking for "munkres" will install the latest (1.1.2) instead of the latest for the supported Python version (1.1.2 or 1.0.12).

https://packaging.python.org/guides/dropping-older-python-versions/ documents best practices for dropping support for given Python versions. It's too late for the drop of Python 2.7 and 3.5 but should be implemented before Python 3.6 gets dropped.

[epeisach]

I agree. I just ran into this issue. Yes having setup.py tell you there is an issue is not sufficient. On python 2, "pip list -o" implies can update to 1.1.2 - which it allowed.

Under classifiers in setup.py you can add:

'Programming Language :: Python :: 3',

or do the python_requires as mentioned in the URL.