Restore pylint: ruff is not a drop-in replacement

[farhan]

Context

During the Python tooling modernization, pylint was replaced with ruff in xblocks-core.

Confusion was perhaps we are replacing ruff with pylint

After further discussion, the team has decided not to replace pylint with ruff.

Ruff will not catch issues like type mis-matches, attribute-undefined, etc.

For repos which are fully type annotated and checked with mypy we can ignore pylint

See the Slack thread for the full discussion: https://openedx.slack.com/archives/C05P7KQURL0/p1786133265985139

Summary of decision (from Feanil Patel):

People are welcome to add ruff, but it's not a replacement for pylint. To replace pylint we'll need to replace some custom pylint plugins + all its type checking.

Decision

• Restore pylint to xblocks-core

[farhan]

Caution

Generated with Claude Code, and not critically reviewed — e.g. the specific ruff rule choices.

@feanil @kdmccormick @openedx/axim-aximprovements

While working on this story I started shaping a strategy for adopting ruff across our Python repos alongside pylint. This is a rough, half-baked plan, feedback is appreciated:

Linting strategy for Open edX Python repos

A consistent setup so pylint and ruff complement each other instead of overlapping.

1. pylint as the first-class linter

It runs the edx_lint plugins and catches what ruff cannot — undefined attributes, type mismatches, too-many-*, and re-export-aware unused-import. It also owns line-too-long.

2. ruff as a second linter, only where it clearly wins

Enable the rule groups pylint does not cover, plus the formatter:

• I isort — import sorting.
• UP pyupgrade — modern syntax.
• B flake8-bugbear — likely bugs.
• C4 flake8-comprehensions — cleaner comprehensions.
• DJ flake8-django — Django checks.
• D pydocstyle — docstring style.

If a repo also enables pycodestyle (E/W) and pyflakes (F) in ruff, disable the two that pylint already owns so there is a single authority: F401 (→ pylint unused-import) and E501 (→ pylint line-too-long).

3. mypy — not by default

Add mypy only when a repo is fully type-annotated and commits to keeping it that way (typically a library with a typed public API). Partial annotations produce noise without real safety, so skip it otherwise. A repo that is fully mypy-checked can drop pylint's type checks.

References

openedx-events and openedx-filters already run pylint and ruff side by side. xblocks-core#294 implements this strategy.