Automatically run flake8 on only your changes before each commit

pre-commit

#!/usr/bin/env python

"""
To use this hook, copy this file to REPOSITORY_NAME/.git/hooks/pre-commit

This pre-commit hook relies mainly on the diff_cover package to check for style
violations only in the lines of code you are about to commit. It's been pretty
awesome for me so far and it's definitely useful when working on legacy code!
In use, it might not be much different than git diff HEAD~1 | flake8 --diff
but I prefer the readability of the diff-quality output.
Check it out here: https://github.com/Bachmann1234/diff-cover

I'm using flake8 here, but diff_cover also supports pep8, pyflakes, and pylint
If you already have a flake8 configuration, then great! If not, it's quite easy
See here: https://flake8.readthedocs.org/en/latest/config.html

"""

import importlib
import subprocess
import sys

requirements = ['diff_cover', 'flake8']
for package in requirements:
    try:
        importlib.import_module(package)
    except ImportError:
        print('Please install {} to use this pre-commit hook'.format(package))
        sys.exit(1)


def main():
    cmd = [
        'diff-quality',
        '--fail-under=100',
        '--violations=flake8',
        '--ignore-unstaged',
    ]
    proc = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
    out, _ = proc.communicate()
    if proc.returncode:
        print(out)
        print("Style violations detected. Please fix them or force the commit with --no-verify")
        sys.exit(proc.returncode)

if __name__ == '__main__':
    main()