Reformat the codebase and enable black check in CI

[Helveg]

No description provided.

[Helveg]

@heplesser @jougs If you could review the none-cake containing commits and merge this before merging any other Python-containing PRs then we have black in.

Prominent changes:

• Added black pre commit hook and enabled CI check; dev docs on the topic was already included in the previous PR Separated checks #2590
• Reformatted the Python codebase and added the commit sha to the ignore revs file so that blame isn't cluttered
• Added E203 to the flake8 ignore list because it is not PEP8 compliant and Black and flake do not agree about it. With black in place, the relevance of a pep8 checker is dubious, because black conforms to PEP8 and leads to a single formatted outcome.

[heplesser]

@Helveg Thank you for this PR. My main concern is that it reduces the line length to 80. While this is in line with PEP8, we have concluded that for C++ code we allow 120, because it makes code more readable. In the diff I noticed numerous lines that are now broken although just slightly over 80, not improving legibility. So I would strongly argue for using 120 also for Python code.

And could you elaborate on the SHAs? I don't quite understand what that is about.

[Helveg]

Oh, I thought I had set the line length config to 120, I will double check! The SHA removes the commit from any git blame checking, otherwise my reformatting commit would show up everywhere as the person last changing that code, and more meaningful history and blame is occluded

[Helveg]

@heplesser I force pushed a new attempt; the line length is now set in pyproject.toml.

Small question: why are so many tool settings set in tox.ini and not in pyproject.toml? Maybe this predates the pyproject.toml support?

[heplesser]

@heplesser I force pushed a new attempt; the line length is now set in pyproject.toml.

Small question: why are so many tool settings set in tox.ini and not in pyproject.toml? Maybe this predates the pyproject.toml support?

@Helveg History is probably the most plausible explanation. I don't think it was an explicit choice of tox.ini in favour of pyproject.toml. I think when I first started with tox (in another context), I came across instructions that gave a minimal "do not change" pyproject file and lots of details of what to put into tox.ini. Feel free to create a new PR with a better structure (and ideally links to documentation of the file formats/purposes).

[heplesser]

I have a few questions concerning places where code had been hand-formatted for readability. I have not systematically searched for all such cases yet, would like your feedback first.

[terhorstd]

LGTM! 👍

[nicolossus]

LGTM!

[Helveg]

@heplesser I am surprised? So we are fine with disrupting all the currently aligned comments in the codebase?

[jougs]

I am fine with this change, but did obviously not look at all the changes