Laid out infrastructure for switching to black formatting all code.

[MicahGale]

Description

The goal of this PR is to actually be PEP8, and enforce it. This does so by:

1. Setting the expectation for using black. Black is best when used universally.
2. Creating a CI job for checking that black was used for formatting all changes with black --check
3. Adding black as an optional dependency.

To avoid confusion this PR does not actually apply black, that is done in #3223.

Fixes #2002

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 15) on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

[MicahGale]

Failure of Python-format-test is to be expected, and shows that the test is working.

[shimwell]

Awesome, particularly keen on this PR as I think it will save a lot of human time reviewing and suggesting minor formatting changes on PRs.

Could also consider changing this line in the PR template

openmc/.github/pull_request_template.md

Line 16 in de8132a

- [ ] I have run [clang-format](https://docs.openmc.org/en/latest/devguide/styleguide.html#automatic-formatting) (version 15) on any C++ source files (if applicable)

[MicahGale]

Awesome, particularly keen on this PR as I think it will save a lot of human time reviewing and suggesting minor formatting changes on PRs.

Could also consider changing this line in the PR template

openmc/.github/pull_request_template.md

Line 16 in de8132a

- [ ] I have run [clang-format](https://docs.openmc.org/en/latest/devguide/styleguide.html#automatic-formatting) (version 15) on any C++ source files (if applicable)

Are you thinking of adding "I have ran black" language to this?

[shimwell]

Are you thinking of adding "I have ran black" language to this?

Yep perhaps good to keep it as a single check box.

Something like

I have run Clang on C++ code changes and Black on Python code changes.

[lewisgross1296]

Thoughts on adding the badge to the README.md? It's purely cosmetic but could be fun and a way for users to find the project.

Looks like python 3.10.0 did go out of SPEC 0 in October, but some of the other minor versions were released after. For example, I'm still using 3.10.5 locally, and that was released in June 2022. What is the policy on SPEC 0 for minor versions?

[MicahGale]

1. I'll give the badge a shot.

2. Yes python 3.10 is out of SPEC 0 now. I'm guessing you meant patch version (third digit). I think spec 0 doesn't care about patch version and only cares about minor versions. I have another open PR Migrate to Python 3.13 #3164 for this migration. You should probably upgrade to python 3.13 or 3.12.

[shimwell]

Is it worth considering using pre commit for black formatting

[MicahGale]

Is it worth considering using pre commit for black formatting

I personally prefer to run black manually. I feel like this is more of a personal developer choice.