Run black+isort on code generated by `gen_exports.py`

[jakkdl]

See #2733 (comment) and #2743 (comment) and #2743 (comment)

Should maybe also report issues that aren't just waiting for release upstream to https://github.com/berkerpeksag/astor

[TeamSpen210]

Would be a nice tidyup, especially since isort should collapse multiple imports, so you can get rid of the basic check I did to prevent those. To maximise cross-platformness, might be best to call them via subprocess.run([sys.executable, "-m", ...]) so we don't require python or the executable to be on PATH.

[jakkdl]

Both of them look to have an API, so we shouldn't need to involve external processes at all

[Zac-HD]

You might want to use shed? It includes Black and Isort, ensures that the results are idempotent, does some further cleanups, and the Python API is easier to use than those of the wrapped tools.

[TeamSpen210]

It'd make more sense to use shed on the whole repo - if we just used it here, we might end up in a situation where it produces different results to running black/isort standalone.

[jakkdl]

It'd make more sense to use shed on the whole repo - if we just used it here, we might end up in a situation where it produces different results to running black/isort standalone.

I was about to make that comment, but even if it does produce slightly different code the problem would only happen if shed output code that doesn't pass black/isort. That in general shouldn't happen - but shed ignores project configs iirc, which could cause a diff if we were to turn on --preview for black, or modify isort settings.

[A5rocks]

I think this is completed now?