Running Black, Flake8, and isort with pre-commit

In this tutorial, we'll explore how to use pre-commit to automate the checking of a Python project with three essential tools:

• Black: For code formatting.
• Flake8: For linting.
• isort: For sorting imports.

What is a Git Commit?

In Git, you can manage your repository using many actions, such as pulling, committing, merging, and pushing code. For this tutorial, we are concerned about commit -- an action that records a snapshot of the changes made to your files in a repository. Commits are used to track the history of a project and allow developers to revert to earlier versions if needed.

What are Git Hooks?

Similar to other Version Control Systems, Git has a way to fire off custom scripts before or after an action takes effect. These scripts are called Git hooks. They allow you to automate tasks and enforce standards at various stages of the Git workflow. For this tutorial, we are particularly interested in using the pre-commit hook, which runs before a commit is finalized.

What is pre-commit?

pre-commit is a tool that manages and executes pre-commit hooks. For our use case, we will use pre-commit to automate running Black, Flake8, and isort. This process performs sanity checks, ensuring our code adheres to standards prior to committing.

To simplify: We want to use pre-commit to perform quality checks prior to saving our work in a Git repository.

How to Use pre-commit?

1. Activate your virtual environment

Before installing pre-commit, you have to activate your virtual environment. A virtual environment helps isolate your project's dependencies from your global Python installation.

2. Install pre-commit via pip

Once your virtual environment is active, download and install pre-commit using pip by entering the following command in your terminal:

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pip install pre-commit

3. Add a pre-commit configuration file

You need to create a file named .pre-commit-config.yaml.

4. Add the settings for Black, Flake8, and isort

Using the Gen EMR project as an example, below is a sample production .pre-commit-config.yaml file from our Django project.

Take note: The .pre-commit-config.yaml should use 2 spaces as a common convention.

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repos:
  # Based on: https://black.readthedocs.io/en/stable/integrations/source_version_control.html
  # Using this mirror lets us use mypyc-compiled black, which is about 2x faster
  - repo: https://github.com/psf/black-pre-commit-mirror
    rev: 24.10.0
    hooks:
      - id: black
      # It is recommended to specify the latest version of Python
      # supported by your project here, or alternatively use
      # pre-commit's default_language_version, see
      # https://pre-commit.com/#top_level-default_language_version
        language_version: python3.12.5

  # Based on: https://flake8.pycqa.org/en/latest/user/using-hooks.html
  - repo: https://github.com/pycqa/flake8
    rev: 7.1.1
    hooks:
      - id: flake8
        additional_dependencies: [flake8-bugbear]

  # Based on: https://pycqa.github.io/isort/docs/configuration/pre-commit.html
  #           https://pycqa.github.io/isort/docs/configuration/black_compatibility.html
  - repo: https://github.com/pycqa/isort
    rev: 5.13.2
    hooks:
      - id: isort
        args: ["--profile", "black", "--filter-files"]

You may want to view the pre-commit's available config options.

5. Install the Git hook scripts

Run the following command to install the hooks defined in your .pre-commit-config.yaml:

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pre-commit install

This command sets up the hooks to run automatically before every commit.

Terminal output:

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pre-commit installed at .git/hooks/pre-commit

6. Run Git hook scripts for all files

If you have added new hooks to your .pre-commit-config.yaml, it is a good idea to run them on all your files.

Type the following code in your terminal:

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pre-commit run --all-files

Terminal output:

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[INFO] Installing environment for https://github.com/psf/black-pre-commit-mirror.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
[INFO] Installing environment for https://github.com/pycqa/flake8.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
[INFO] Installing environment for https://github.com/pycqa/isort.
[INFO] Once installed this environment will be reused.
[INFO] This may take a few minutes...
black................................................(no files to check)Skipped
flake8...............................................(no files to check)Skipped
isort................................................(no files to check)Skipped