Create bytes from properties

def to_bytes(self):
        '''
        Create bytes from properties
        '''
        # Verify that the properties make sense
        self.sanitize()

        # Write the version
        bitstream = BitStream('uint:4=%d' % self.version)

        # Write the traffic class
        bitstream += BitStream('uint:8=%d' % self.traffic_class)

        # Write the flow label
        bitstream += BitStream('uint:20=%d' % self.flow_label)

        # Write the payload length
        payload_bytes = bytes(self.payload)
        payload_length = len(payload_bytes)
        bitstream += BitStream('uint:16=%d' % payload_length)

        # Write the next header type
        bitstream += BitStream('uint:8=%d' % self.next_header)

        # Write the hop limit
        bitstream += BitStream('uint:8=%d' % self.hop_limit)

        # Write the source and destination addresses
        bitstream += BitStream('uint:128=%d, '
                               'uint:128=%d' % (int(self.source),
                                                int(self.destination)))

        return bitstream.bytes + payload_bytes