git filter among repos

repo.py

import os
from subprocess import check_output, CalledProcessError


def get_repo_paths(root=None):
    repo_paths = []
    for dir, _, _ in os.walk(root):
        if dir.endswith('/.git'):
            repo_paths.append(dir[:-5])
    return repo_paths


def get_commit_ids_by_permission(repo_path=None, permission=None):
    if permission is None:
        permission = '.*'

    current_path = os.getcwd()
    os.chdir(repo_path)
    template_git_command = ["git", "log", "--pretty=format:%h"]
    permission_rex = "<.*uses-permission.*\." + permission + ".*/>"
    template_permission = ["-G", permission_rex]
    template_path = ["--", "*AndroidManifest.xml"]
    command = []
    command.extend(template_git_command)
    command.extend(template_permission)
    command.extend(template_path)
    output = check_output(command)
    try:
        output = check_output(command)
    except CalledProcessError:
        commit_ids = []
    os.chdir(current_path)
    commit_ids = output.split()
    return commit_ids

root = '../repo'
for repo_path in get_repo_paths(root):
    print ">>>", repo_path
    print len(get_commit_ids_by_permission(repo_path))

The following result represent that `../repo/github/android' repo has 10 commits related to all permisissions in all AndroidManifest.xml.

$ python repo.py 
>>> ../repo/gihub/android
10
>>> ../repo/johnkil/Android-AppMsg
0
>>> ../repo/owncloud/android
6

FIXME:
However, some repositories make fatal error due to no head which means that the repository is not well formed. I can't handle that kind of error even I used try and except.