list django template's inheritance hierarchy

#!/usr/bin/env python
import os
import re
import sys
import json
import itertools
import collections

def list_templates():
    from django.template.loaders.app_directories import app_template_dirs
    res = []
    for dirpath, dirs, fnames in itertools.chain(*(os.walk(path) for path in app_template_dirs)):
        for fname in fnames:
            if os.path.splitext(fname)[1] == '.html' and 'templates' in dirpath:
                filepath = os.path.join(dirpath, fname)
                res.append(os.path.join(filepath))
    return res


def search_file(filepath, regex):
    if filepath in exhausted_templates:
        return None

    with open(filepath) as f:
        for l in f:
            res = regex.search(l)
            if res:
                exhausted_templates.append(filepath)
                return res
    return None


def find_children(path, template_name):
    reg = re.compile(
        r"""\{\%%\s*extends\s+[\'\"]%s[\'\"]\s*\%%\}""" % template_name)
    res = []
    for filepath in templates:
        if search_file(filepath, reg):
            res.append(os.path.join(filepath))
    return res


def Tree():
    return collections.defaultdict(Tree)


if __name__ == '__main__':
    if len(sys.argv) < 2:
        print '''Example:
        DJANGO_SETTINGS_MODULE=mysite.settings %s base.html
        ''' % sys.argv[0]
        sys.exit(1)

    templates = list_templates()
    exhausted_templates = []

    tree = Tree()
    template_reg = re.compile(r'^.*?/templates/')

    def fulfill(tree, template_name):
        template_name = template_reg.sub('', template_name)
        sub_tree = tree[template_name]
        for fname in find_children('.', template_name):
            fulfill(sub_tree, fname)

    top = sys.argv[1]
    fulfill(tree, top)
    print(json.dumps(tree, indent=4))