<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def getSignedNS(self, ns_uri):
 """Get signed arguments from the response message. Return a dict of all arguments in the specified namespace. If any of the arguments are not signed, return None. """

        msg_args = self.message.getArgs(ns_uri)

        for key in msg_args.iterkeys():
            if not self.isSigned(ns_uri, key):
                logging.info("SuccessResponse.getSignedNS: (%s, %s) not signed."
                            % (ns_uri, key))
                return None

        return msg_args