The basics

An overview on contributing to the Black project.

Technicalities

Development on the latest version of Python is preferred. As of this writing it’s 3.9. You can use any operating system.

Install all development dependencies using:

$ pipenv install --dev
$ pipenv shell
$ pre-commit install

If you haven’t used pipenv before but are comfortable with virtualenvs, just run pip install pipenv in the virtualenv you’re already using and invoke the command above from the cloned Black repo. It will do the correct thing.

Non pipenv install works too:

$ pip install -r test_requirements.txt
$ pip install -e .[d]

Before submitting pull requests, run lints and tests with the following commands from the root of the black repo:

# Linting
$ pre-commit run -a

# Unit tests
$ tox -e py

# Optional Fuzz testing
$ tox -e fuzz

# Optional CI run to test your changes on many popular python projects
$ black-primer [-k -w /tmp/black_test_repos]

News / Changelog Requirement

Black has CI that will check for an entry corresponding to your PR in CHANGES.md. If you feel this PR does not require a changelog entry please state that in a comment and a maintainer can add a skip news label to make the CI pass. Otherwise, please ensure you have a line in the following format:

- `Black` is now more awesome (#X)

Note that X should be your PR number, not issue number! To workout X, please use Next PR Number. This is not perfect but saves a lot of release overhead as now the releaser does not need to go back and workout what to add to the CHANGES.md for each release.

Style Changes

If a change would affect the advertised code style, please modify the documentation (The Black code style) to reflect that change. Patches that fix unintended bugs in formatting don’t need to be mentioned separately though.

Docs Testing

If you make changes to docs, you can test they still build locally too.

$ pip install -r docs/requirements.txt
$ pip install [-e] .[d]
$ sphinx-build -a -b html -W docs/ docs/_build/

black-primer

black-primer is used by CI to pull down well-known Black formatted projects and see if we get source code changes. It will error on formatting changes or errors. Please run before pushing your PR to see if you get the actions you would expect from Black with your PR. You may need to change primer.json configuration for it to pass.

For more black-primer information visit the documentation.

Hygiene

If you’re fixing a bug, add a test. Run it first to confirm it fails, then fix the bug, run it again to confirm it’s really fixed.

If adding a new feature, add a test. In fact, always add a test. But wait, before adding any large feature, first open an issue for us to discuss the idea first.

Finally

Thanks again for your interest in improving the project! You’re taking action when most people decide to sit and watch.