pep8 and pyflake as git hook

pre-commit.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""
Script to run pep8 and pyflakes via git's pre-commit hook

Based on https://github.com/lbolla/dotfiles/blob/master/githooks/pre-commit
Modified by Martin Gaitán <[email protected]> for Machinalis (www.machinalis.com)

Install:

Copy it as REPO/.git/hooks/pre-commit given execution permission

Usage:

    Just commit your changes as usual.

    When python files were modified, it run pep8 and pyflakes.
    If no errors, the commit is done, else it exist given
    useful output

    To skip the hook and force the commit add -n:

    $ git commit -n

"""

import os
import sys
import subprocess

MAX_LINE_LENGHT = 90
AUTO_ADD_STAGED_MODIFIED = True

devnull = open(os.devnull, 'w')


def call(cmd, cwd=None):
    p = subprocess.Popen(cmd.split(),
                         stdout=subprocess.PIPE,
                         stderr=subprocess.PIPE,
                         cwd=cwd)
    out, err = p.communicate()
    return out.decode('utf-8'), err.decode('utf-8'), p.returncode


def execute(cmd, silent=False):
    if silent:
        params = {
                'stdout': devnull,
                'stderr': devnull,
                }
    else:
        params = {}
    retcode = subprocess.call(cmd.split(), **params)
    return retcode


def exists(cmd):
    return execute('which %s' % cmd, silent=True) == 0


def get_staged(ext, auto_add=True):
    out, _, _ = call('git diff --name-only --staged')
    staged = set(out.splitlines())
    if auto_add:
        out, _, _ = call('git diff --name-only')
        staged_modified = set(out.splitlines()).intersection(staged)
        for filename in staged_modified:
             call('git add %s' % filename)
    return [f for f in staged if f.endswith(ext)]


def output(prg, out, err):
    print(' * %s:\n%s\n%s' % (prg, out, err))


def die(msg):
    print(msg)
    sys.exit(1)


def check_python():
    has_pep8 = exists('pep8')
    has_pyflakes = exists('pyflakes')
    if not (has_pep8 or has_pyflakes):
        die('Install PEP8 and PyFlakes!')

    staged = get_staged('py', AUTO_ADD_STAGED_MODIFIED)
    if not staged:
        return

    rrcode = 0
    for filename in staged:
        out, err, _ = call('pep8 --max-line-length=%d %s' %
                            (MAX_LINE_LENGHT, filename))
        if out or err:
            output('pep8', out, err)
            rrcode = rrcode | 1
        retcode = execute('pyflakes %s' % filename)
        rrcode = retcode | rrcode

    if rrcode != 0:
        sys.exit(rrcode)


def main():
    check_python()


if __name__ == '__main__':
    main()