How to use the rdt.RealChallenge.compute function in rdt

OPTIONS, DESCRIBE, SETUP, SET_PARAMETER, SET_PARAMETER, PLAY
        Returns True if it sent a packet, False if it didn't """
        if not self.sent_options:
            self.sent_options = True
            self._sendOptions()
            return True
        if not self.sent_describe:
            print 'sending describe'
            self.sent_describe = True
            self._sendDescribe()
            return True
        if len(self.streamids) > len(self.setup_streamids):
            headers = {}
            if not self.sent_realchallenge2:
                self.sent_realchallenge2 = True
                challenge_tuple = RealChallenge.compute(self.realchallenge1)
                headers['RealChallenge2'] = '%s, sd=%s' % challenge_tuple
            # Gets a streamid that hasn't been setup yet
            s = [s for s in self.streamids if s not in self.setup_streamids][0]
            self.setup_streamids.append(s)
            self._sendSetup(streamid=s, headers=headers)
            return True
        if not self.sent_parameter:
            self.sent_parameter = True
            self._sendSetParameter('Subscribe', self.subscribe)
            return True
        if not self.sent_bandwidth:
            self.sent_bandwidth = True
            self._sendSetParameter('SetDeliveryBandwidth',
                              'Bandwidth=%s;BackOff=0' % self.factory.bandwidth)
            return True
        if not self.sent_play: