How to use Black, Pylint and Mypy in GitHub Actions?

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 Github Actions workflow will check your code when a Pull Request is created, catching problems before they’re merged.

How to add the Github Actions workflow

Add the following to your repository in .github/workflows/code-quality.yml.

name: Checks
on: [pull_request]

jobs:
  build:
    runs-on: ubuntu-latest
    name: Checks
    steps:
    - uses: actions/checkout@v2
    - uses: actions/setup-python@v2
      with:
        python-version: 3.x
    - run: pip install --upgrade pip
    - run: pip install "black<23" pylint==v3.0.0a3 mypy==v0.902
    - run: black --diff --check $(git ls-files '*.py')
    - run: pylint --disable=all --enable=unused-import $(git ls-files '*.py')
    - run: mypy --strict $(git ls-files '*.py')

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. This is why I use “black<23” above – we take all updates from this year but not next.
• If you have an existing project with unformatted code, format the entire codebase all at once. Don’t do it gradually.

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