Unignore and enforce check E203 ("Whitespace before colon")

[ShadowJonathan]

(E203 checks "Whitespace before ':' ")

According to setup.cfg, E203 is partly ignored because it's 'contrary to PEP8'. After a bit of research i found out that it is due to colons in slice indexes, which is covered under PEP8.

Going down the rabbithole a bit further, I found PyCQA/pycodestyle#373 and PyCQA/pycodestyle#914, so I suggest tracking those issues and removing E203 once these are resolved, merged, and shipped.

[clokep]

This sounds more like we'd just let black handle where to put that whitespace and not really worry about flake8 here?

[erikjohnston]

Yup, it feels like black is covering this case and so we can safely turn off the flake8 checking of it. I don't think its worth digging into if that's the case