pep8 and pyflake as git hook

pre-commit.py

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

"""
An 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 <mgaitan@machinalis.com>

Install:

 copy it as your REPO/.git/hooks/pre-commit given execute 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 you should use: 
    $ git commit -n
"""

import os
import sys
import re
import subprocess

MAX_LINE_LENGHT = 90
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_modified(ext):
    modified = re.compile('^(?:M|A).(?P<name>.*\.%s)' % ext)
    out, _, _ = call('git status --porcelain')
    modifieds = []
    for line in out.splitlines():
        match = modified.match(line.strip())
        if (match):
            modifieds.append(match.group('name'))
    return modifieds


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!')

    modifieds = get_modified('py')
    if not modifieds:
        return

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

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


def main():
    check_python()


if __name__ == '__main__':
    main()