PEP8 provides guideline on writing python code. To make the compliance to the guideline easy, one can automate this process. There are two ways to achieve this: pre-commit check and github actions. Today, we will talk about how to implement pre-commit check.

pre-commit check installs hooks to a git repo, and when committing new code, the hooks will be triggered. Let’s start.

Step 1. Install pre-commit package

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pip install pre-commit

After this, add ‘pre-commit’ to the ‘requirements.txt’ file so that this package is always installed.

Step 2. Add hooks

One need create a config file .pre-commit-config.yaml at the root of the repo to add hooks.

One example configuration with black and flake8 hooks is as follows:

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# See https://pre-commit.com for more information
# See https://pre-commit.com/hooks.html for more hooks
repos:
  - repo: https://github.com/psf/black
    rev: stable
    hooks:
      - id: black
        language_version: python3.7
  - repo: https://gitlab.com/pycqa/flake8
    rev: 3.8.4
    hooks:
      - id: flake8

The config file is basically telling pre-commit where to download hooks and which hook version to use. See https://pre-commit.com/hooks.html for more information.

Step 3. Install hooks

To install the configured hooks to the repo, one need run

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pre-commit install

and this will install hooks to the .git/hooks folder.

Step 4. Configure flake8

To make the hooks run as expected, one may want to set up configuration for flake8, one example file is like this:

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[flake8]
ignore = E203, E266, E501, W503, F403, F401
max-line-length = 79
max-complexity = 18
select = B,C,E,F,W,T4,B9

This config file sets some options used by flake8.

Step 5. Configure Black

Similarly, one can also configure black. For this, one need do it in the pyproject.toml file. One example file is as follows:

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[tool.black]
py36 = true
line-length = 79
include = '\.pyi?$'
exclude = '''
/(
    \.git
  | \.hg
  | \.mypy_cache
  | \.tox
  | \.venv
  | _build
  | buck-out
  | build
  | dist

  # The following are specific to Black, you probably don't want those.
  | blib2to3
  | tests/data
)/

Here, we set parameter line-length to match max-line-length, otherwise black and flake8 will conflict. For other parameters, check the command options of black.

Step 6. Format existing files

This step is optional, but for existing files in the project, one may run the following command to format existing files:

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pre-commit run --all-files

All done!!!

Then from now on, every time a commit is added to the repo, the hooks will be triggered. If any changes are made by black, the commit would fail. One can review the changes, and modify if necessary, and commit again, until succeed.

References

1. https://dev.to/m1yag1/how-to-setup-your-project-with-pre-commit-black-and-flake8-183k

2. https://medium.com/staqu-dev-logs/keeping-python-code-clean-with-pre-commit-hooks-black-flake8-and-isort-cac8b01e0ea1

Last modified on 2021-01-23