Code Quality: Additional lints in this repository (help wanted!)

We’re doing a bunch of code quality cleanup, and as part of that effort I’d like to implement some additional lints/coding conventions. There will be a lot of manual changes here, so I think these will be some items to have multiple people tackle.

In no particular order:

• ~Add ban-relative-imports = true to .flake8 and remove relative imports from the repo.~
• ~Add flake8-type-checking==1.0.4 to .pre-commit-config.yaml with enable-extensions = TC, TC2 in .flake8, and rework our type annotations for zero runtime cost using string constants. When we drop Python 3.6 support, pyupgrade will be used to automatically switch to from __future__ import annotations and unquote the annotations.~
• ~Add flake8-use-fstring==1.3 to .pre-commit-config.yaml and fix all the use of .format() on string constants in the repo. Start at level 0, and try level 1 if possible. Level 2 is likely useless in this repo (I think we will always use .format() on string variables), but you could prove me wrong.~
• ~Remove E501 from .flake8 – currently, black leaves our long comments, docstrings, and string constants alone – let’s hand-format them to comply with the line length limit.~

Please call dibs in this issue to prevent duplicated effort.

(suggestions for additional code quality improvements/tools to enforce them are also welcomed here)

[finswimmer]

I learned about nitpick these days. I wonder if we like to use it, to enforce a minimum set of checks across our repos?

[dimbleby]

I find quite a lot to like in flake8-pie.

Not sure I agree with absolutely everything it warns about, but you can always disable the things that you don’t want.

(I don’t plan to work on adding this to the repository, if anyone wants to have a go then we will not be duplicating one another.)