Merge extend-ignore and ignore values for flake8

[hendrikmakait]

Merges ignore and extend-ignore config options for flake8, as extend-ignore makes little sense when ignore is also configured and therefore overriding defaults.

This PR

• aligns ignore list with black v.4.0.1
• ignores E402 in tests to silence errors on pytest.importorskip (see Allow for exceptions for E402 PyCQA/pycodestyle#472)
• fixes any other flake8 issues resulting in the changes

• Tests added / passed
• Passes pre-commit run --all-files

[graingert]

I think It's better to keep extend-ignore and remove the regular ignore

[hendrikmakait]

I would be fine with this, one benefit I saw from keeping the ignore list and moving things there is that the default rules for ignore may change from version to version. By maintaining ignore, which currently maps to the defaults, we can effectively pin these.

If we assume that whatever rules flake8 selects as defaults are probably a good idea, I'd be more than happy to keep this rule-set even smaller. Since we pin the version of flake8 itself, this should not result in any surprises outside of a flake8 update.

[fjetter]

I'm fine either way. FWIW, I am usually an advocate for strict linting. I trust the two of you to find a good configuration

[hendrikmakait]

Not sure where I got my earlier defaults for flake8 from, but these are the actual ones: ['E121', 'W504', 'E123', 'W503', 'E24', 'E126', 'E226', 'E704']. This means that a bunch of rules have changed. For comparison, black uses ignore = E203, E266, E501, W503. Given our previous selection, this feels like a reasonably strict set of rules and would mean that we mainly have to start fixing import formatting E4**.

[hendrikmakait]

Maybe we should sprinkle E402 in there, it's the only rule that's failing a lot due to

distributed/distributed/shuffle/tests/test_shuffle.py

Line 13 in 3551d15

pa = pytest.importorskip("pyarrow")

and similar imports.

[hendrikmakait]

Silenced E402 for tests.

[hendrikmakait]

@fjetter: I have made significant changes since your last review. Could you give it another look please?

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

       15 files  ±0         15 suites  ±0   10h 6m 47s ⏱️ + 27m 44s
  2 907 tests ±0    2 821 ✔️  - 2    82 💤 ±0  4 ❌ +2 
21 525 runs  ±0  20 570 ✔️ +1  950 💤  - 2  5 ❌ +1 

For more details on these failures, see this check.

Results for commit 0b377d0. ± Comparison against base commit 1bfd99c.

[graingert]

Black ignores this because they use a different error code for line too long, we shouldn't ignore it