Add pylint

[zundertj]

For discussion

https://github.com/PyCQA/pylint is a different, and arguably more strict linter than flake8. This PR shows the impact by fixing issues on several files (almost, still some errors). I have added some acceptable (up for discussion) errors in pyproject.toml, but there are probably more.

To run locally, when having installed pylint and inside the py-polars dir:

pylint polars

[ghuls]

Personally I am not a fan of the removal of elif and else after a return statement or with raises, as the "branching" code is less clear for me (although the code does exactly the same).

I think it can be disabled with: no-else-raise and no-else-return

On a project I recently worked on, the following lints were disabled:

disable=raw-checker-failed,
        bad-inline-option,
        locally-disabled,
        file-ignored,
        suppressed-message,
        useless-suppression,
        deprecated-pragma,
        use-symbolic-message-instead,
        invalid-name,
        too-many-instance-attributes,
        too-many-arguments,
        unused-argument,
        wrong-import-order,
        missing-module-docstring,
        missing-class-docstring,
        missing-function-docstring,
        too-many-branches,
        too-many-nested-blocks,
        no-else-break,
        broad-except,
        pointless-string-statement,
        use-list-literal,
        no-else-raise,
        no-else-return

50561fe#diff-4c94e013bf5cbe1352b49c01958d0a6d58948f0abf030bf26f6f6c9089e4706eL281-R287

[stinodego]

There's definitely some nice lints in pylint. Thanks for looking into this! I think most are available in flake8 as well through the plugin system. I propose we keep the discussion to the related issue #4044.

[ritchie46]

I think we can incrementally add the lints we'd like with flake8 so I am closing this for now.