r'/foo/<id:\d+>.json' を r'^/foo(?P<id>\d+)\.json$' へと変換するサンプルコード

compile_urlpath.py

# -*- coding: utf-8 -*-

## license: public domain

import re

URLPATH_PARAM_PATTERN = r'<(\w+)(?::(.*?))?>'

re_escape = lambda s: re.escape(s).replace(r'\/', '/')

def compile_urlpath(urlpath, default_pat='[^/]'):
    buf = ['^']; add = buf.append
    pos = 0
    for m in re.finditer(URLPATH_PARAM_PATTERN, urlpath):
        text = urlpath[pos:m.start(0)]
        add(re_escape(text))
        pos = m.end(0)
        name, pat = m.groups()
        add("(?P<%s>%s)" % (name, pat or default_pat))
    add(re_escape(urlpath[pos:]))
    add('$')
    return "".join(buf)


if __name__ == '__main__':
    urlpath = r'/api/posts/<slug>/comments/<comment_id:\d+>.json'
    result = compile_urlpath(urlpath)
    print(repr(result))
      #=> r'^/api/posts/(?P<slug>[^/]+)/comments/(?P<comment_id>\d+)\.json$'