Returns a tuple (reverse string, group count) for a url.

        For example: Given the url pattern /([0-9]{4})/([a-z-]+)/, this method
        would return ('/%s/%s/', 2).

def _find_groups(self) -> Tuple[Optional[str], Optional[int]]:
        """Returns a tuple (reverse string, group count) for a url.

        For example: Given the url pattern /([0-9]{4})/([a-z-]+)/, this method
        would return ('/%s/%s/', 2).
        """
        pattern = self.regex.pattern
        if pattern.startswith("^"):
            pattern = pattern[1:]
        if pattern.endswith("$"):
            pattern = pattern[:-1]

        if self.regex.groups != pattern.count("("):
            # The pattern is too complicated for our simplistic matching,
            # so we can't support reversing it.
            return None, None

        pieces = []
        for fragment in pattern.split("("):
            if ")" in fragment:
                paren_loc = fragment.index(")")
                if paren_loc >= 0:
                    pieces.append("%s" + fragment[paren_loc + 1 :])
            else:
                try:
                    unescaped_fragment = re_unescape(fragment)
                except ValueError:
                    # If we can't unescape part of it, we can't
                    # reverse this url.
                    return (None, None)
                pieces.append(unescaped_fragment)

        return "".join(pieces), self.regex.groups