Git: rev-parse

import subprocess, os

repo_dir = os.path.expanduser('~/git/dchelper')

command = ['git', 'rev-parse', '--is-inside-work-tree']
process = subprocess.Popen(command, stdout=subprocess.PIPE, cwd=repo_dir)
output = process.communicate()  # (b'true\n', None)
res = output[0].decode().strip()
if res == 'true':
    print('--is-inside-work-tree')