Style checking Python programs in CI

[athas]

We have a bunch of Python programs in tools/, but where our Haskell code is closely scrutinized by such things as hlint, ormolu, and GHC itself, no such thing has been set up for Python.

I have no idea what kind of linters are commonly used for Python, but someone should investigate and set it up.

[kfl]

I recommend:

• pep8 as style checker https://pypi.org/project/pep8/ (a bit like hlint)
• black as formatter https://pypi.org/project/black/ (like ormolu)
• mypy as type checker https://www.mypy-lang.org/ (but that's a bit of an investment)

I've been recommended flake8 https://github.com/pycqa/flake8, but personally I've found it too big an investment compared to the gains.

[WilliamDue]

Thanks @kfl this was very helpful!