addtrailingcommas.py

#!/usr/bin/env python
"""
This script assumes you have both flake8 and flake8-commas packages
installed in the Python environment you use to run this script.
"""

import subprocess
import sys
from collections import defaultdict

MISSING_TRAILING_COMMAS = 'missing trailing comma'


def extract_missing_commas(violations):
    paths_missing_commas = defaultdict(lambda: defaultdict(list))
    for violation in out.strip().split('\n'):
        if violation.endswith(MISSING_TRAILING_COMMAS):
            path, line, char, _ = violation.split(':')
            paths_missing_commas[path][int(line)] = int(char) - 1
    return sorted(paths_missing_commas.items())


def add_missing_commas(path, locations):
    with open(path, 'r') as file_:
        lines = []
        for line, content in enumerate(file_, start=1):
            char = locations.get(line)
            if char:
                content = '%s,%s' % (content[0:char], content[char:])
            lines.append(content)
    with open(path, 'w+') as file_:
        file_.writelines(lines)


if __name__ == '__main__':
    sys.stdout.write('Running flake8 to detect missing trailing commas... ')
    sys.stdout.flush()
    process = subprocess.Popen(
        'flake8 %s' % ' '.join(sys.argv[1:]),
        shell=True,
        stdout=subprocess.PIPE,
        stderr=subprocess.PIPE,
    )
    out, err = process.communicate()
    sys.stdout.write('done.\n')

    violations = out.strip().split('\n')
    for path, locations in extract_missing_commas(violations):
        sys.stdout.write('Adding missing commas to "%s"... ' % path)
        sys.stdout.flush()
        add_missing_commas(path, locations)
        sys.stdout.write('done.\n')