<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_supported_methods(self, url):
 """Get a list of supported methods for a url and optional host. :param url: URL string (including host) :return: frozenset of supported methods """

        route = self.routes_all.get(url)
        # if methods are None then this logic will prevent an error
        return getattr(route, "methods", None) or frozenset()