Setting up pre-commit in python project

Tools like pre-commit help ensure all checks (type checking, linting, formatting, etc.) are run before code is committed. It integrates easily with Git and runs defined hooks automatically when git commit is executed.

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Why Use pre-commit?

• Catch issues early (before code hits CI or production)
• Enforce consistent formatting and style
• Automate repetitive checks (e.g., black, flake8, mypy)
• Save time during code review

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Step-by-Step Setup

1. Install pre-commit

pip install pre-commit

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2. Create the .pre-commit-config.yaml File

This file must be placed at the root of your Git repository.

Example configuration:

repos:
  - repo: https://github.com/psf/black
    rev: 24.3.0
    hooks:
      - id: black

  - repo: https://github.com/pycqa/flake8
    rev: 6.1.0
    hooks:
      - id: flake8

  - repo: https://github.com/pre-commit/mirrors-mypy
    rev: v1.9.0
    hooks:
      - id: mypy

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3. Install the Git Hook Scripts

Run this once to install hooks:

pre-commit install

Now every time you try to git commit, your configured hooks will run first.

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4. Run Checks Manually (Optional)

If you want to run all hooks against all files manually:

pre-commit run --all-files

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Best Practices

• Add .pre-commit-config.yaml to your repo
• Add pre-commit to your requirements.txt or pyproject.toml
• Include it in onboarding docs for contributors
• Use consistent versions of hooks with rev: pinning
• Use it alongside tox, pytest, mypy, etc.

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Further Reading

• Pre-commit official documentation
• Git hook reference
• Example Python pre-commit config