Catch Bugs Before You Commit (ruff + mypy)

Why this matters

Ruff (also from Astral) replaced the entire linter stack — pyflakes, pycodestyle, pylint, isort, even Black for formatting. It's 10–100× faster and reads its config from pyproject.toml. Mypy adds type checking on top. The 2026 baseline: ruff check + ruff format + mypy --strict in CI, with project-specific allows in pyproject.toml. A team that adopts both from day 1 has clean code forever; a team that doesn't will fight 10 paper cuts a week.

Demo

Ruff is a Rust-based linter and formatter that replaces pyflakes, pycodestyle, isort, pyupgrade, and Black in a single binary, running 10-100× faster than any of them individually. It reads all configuration from [tool.ruff] in pyproject.toml, which means one file governs both linting rules and formatting style for your entire team. Layering mypy on top adds static type checking — when both run in a pre-commit hook or CI step, the feedback loop from 'I wrote a bug' to 'the tool caught it' shrinks to under a second.

Try it yourself

1. Add the [tool.ruff] section to a real project. Run ruff check . and fix every finding (most are auto-fixable with ruff check --fix).
2. Run ruff format . on a Python file with mixed quoting / spacing. It rewrites it to one canonical style.
3. Add [tool.mypy] with strict = true. Run mypy src/. Expect findings — strict mode is uncompromising on first use.
4. Wire all three into a pre-commit hook. Total runtime should be sub-second on a small project.

References

• Ruff
• Mypy
• PEP 484 — Type Hints