PEP8 fixes

[cclauss]

Describe the tool ruff, how it finds three pep8 issues, and how it fixes those 3 issues.

Ruff supports over 500 lint rules and can be used to replace Flake8 (plus dozens of plugins), isort, pydocstyle, yesqa, eradicate, pyupgrade, and autoflake, all while executing (in Rust) tens or hundreds of times faster than any individual tool.

% ruff --select=E703,E712,E713 --statistics .

 12	E703	[*] Statement ends with an unnecessary semicolon
105	E712	[*] Comparison to `False` should be `cond is False`
 13	E713	[*] Test for membership should be `not in`

% ruff --select=E703,E712,E713 --fix .

Found 130 errors (130 fixed, 0 remaining).

[skirpichev]

Seems ok, but please ensure, that these errors are tested in CI. Could you also make commit message more descriptive?

[skirpichev]

Few unrelated changes, but LGTM.
Let's wait few days if someone will object against changes. Code style changes always debatable.