How to use Black, Pylint and Mypy in Pre-commit?

Python’s not the strictest language, so to have any confidence in your code you need to hit it with a barrage of checks to ensure it meets at least some level of quality.

I use the following code quality checks:

• Black to ensure code is formatted,
• Pylint to disallow unused imports, and
• Mypy for type checking.

The following Pre-commit hooks will check your code when you try to commit, catching problems before they reach your repository.

How to install the Pre-commit hooks

Add the following .pre-commit-config.yaml file to the root of your repository.

fail_fast: true

repos:
  - repo: https://github.com/ambv/black
    rev: 22.3.0
    hooks:
      - id: black
        args: [--diff, --check]

  - repo: https://github.com/pre-commit/mirrors-pylint
    rev: v3.0.0a3
    hooks:
      - id: pylint
        args: [--disable=all, --enable=unused-import]

  - repo: https://github.com/pre-commit/mirrors-mypy
    rev: v0.902
    hooks:
      - id: mypy
        exclude: ^tests/
        args: [--strict]

Install Pre-commit and add the git hooks:

pip install precommit
pre-commit install

Notes on Black

• Choose a specific Black version and be consistent with it. The formatting can change between versions, so what’s considered “formatted” in one version may not be in another. Note as of 2022 Black has a Stability Policy which states the formatting won’t change in a calendar year.
• If you have an existing project with unformatted code, format the entire codebase all at once. Don’t do it gradually.

Recommended: How to use Black, Pylint and Mypy in Github Actions?