Python: py_samples could run blacken

[tswast]

The noxfile.py in the samples template now includes a blacken session. It's great to run this, but I notice that the changes it makes get reverted the next time that synthtool runs. I think it makes sense for blacken to blacken the noxfile, but if used then it shouldn't get reverted.

Since I'm not sure if all of our samples are using black, I propose we add an optional parameter to py_samples that runs blacken when done copying everything.

Reference:

• "unblacken" PR: chore: unblacken snippets noxfile python-bigquery-reservation#66

• synthtool/synthtool/languages/python.py

  Line 96 in 996775e

  def py_samples(*, root: PathOrStr = None, skip_readmes: bool = False) -> None:

[tswast]

Confirmed that this needs to be an opt-in parameter.

[tswast]

On second thought, I see that blacken is actually called via the shell command.

https://github.com/googleapis/python-bigquery-reservation/blob/2acdeb782521c01a4e1fa01e42fdd1ce79dbf13d/synth.py#L66

Perhaps what is needed is to do the same for each samples directory?

[tswast]

It was actually quite simple to blacken all samples. I don't think this requires any changes to synthtool.

import pathlib

REPO_ROOT = pathlib.Path(__file__).parent.absolute()

# ...

# ----------------------------------------------------------------------------
# Final cleanup
# ----------------------------------------------------------------------------

s.shell.run(["nox", "-s", "blacken"], hide_output=False)
for noxfile in REPO_ROOT.glob("samples/**/noxfile.py"):
    s.shell.run(["nox", "-s", "blacken"], cwd=noxfile.parent, hide_output=False)