STY Enables black with experimental_string_processing=true

[thomasjpfan]

Reference Issues/PRs

Resolves #20365

What does this implement/fix? Explain your changes.

This should be merged with the "rebase and merge" option to keep the two commits separate:

1. MAINT Adds experimental_string_processing to pyproject.toml
2. STY Runs black with experimental_string_processing=true

[thomasjpfan]

The doc error is being fixed here: #20410

[ogrisel]

I did a manual review of ~30 files at random and could not spot any issue. It generally improves things a lot. I think we can trust the tests for this change to be correct. Doing a full review of this diff is going to be tedious.

Note: there plenty of cases where the code could be even cleaner / simpler by using f-strings instead of .format() or %-based string interpolation but this can be improved progressively later.

[rth]

Note: there plenty of cases where the code could be even cleaner / simpler by using f-strings instead of .format() or %-based string interpolation but this can be improved progressively later.

Yes, if we are into such automatic code changes, running pyupgrade on the code would perform a migration to f-strings. But then this means that such tooling would also need to be available for people solving PR merge conflicts, so what's a good compromise there remains to be determined. Maybe something we can talk about at the meeting.

[ogrisel]

Edit: #20410 was merged. I think you should rebase this on top of main to make sure CI is 100% green before merging.

Edit2: actually there are conflicts, so the black step should be re-run :)

[ogrisel]

@rth shall we merge this one? The CI is green and there are no conflicts but it won't last long I think.

[rth]

Yes, thanks @thomasjpfan !