[WIP] Validate PEP-8 in docstrings

[dubielt1]

• closes Validate PEP-8 in docstring examples #23154
• tests added
• tests passed
• passes git diff upstream/master -u -- "*.py" | flake8 --diff
• whatsnew entry

Potential blocks to closing

• Adds dev dependency on pycodestyle, as I couldn't get the other libraries (such as pyflakes) to accept a string for PEP-8 validation, they all expect file names to read.
• When printing the PEP-8 violations, the line numbers printed are with respect to the Example heading, e.g. the first example >>> ... is line 1. I tried reporting the actual file line number using doctest.Example.lineno, but it fails to report the correct line number when the docstring is defined outside of the function/method, and possibly modified as well? (e.g. pandas.io.excel.read_excel)

Tests added / passed

• I haven't added tests yet, but plan to add some with PEP-8 violations to test_validate_docstrings.py

whatsnew

• This is my first PR, not sure if I did this as expected

[pep8speaks]

Hello @dubielt1! Thanks for submitting the PR.

• There are no PEP8 issues in the file scripts/validate_docstrings.py !

[datapythonista]

Sorry @dubielt1 didn't see this PR until now.

The issue has already been fixed in #23399. Closing.

@FHaase, can you take a look to this PR, and see if there is anything that makes sense adding/changing to what you did?

[FHaase]

Reading issue #23154 made me google for flake8 plugins, finding flake8_rst and flake8-docstrings.
After mentioning them in the issue discussion a couple days passed without any reaction so I looked into integrating flake8_rst. Didn't really want to steal @dubielt1's first PR.

From what I understand his idea is using DocTestParser to get the tests into pycodestyle.
We've done basically the same (examples_source_code() to get the tests, but flake8 which includes pycodestyle for generating the issues).

[datapythonista]

Just wanted to make sure there was nothing in the PR that could be useful.

And it's unfortunate that we duplicate work, but it happens all the time in a project like pandas. Not sure if we can do much better than what we do on that.

Thanks for looking at this.