Create bytes from properties

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

        # Write the source and destination ports
        bitstream = BitStream('uint:16=%d, '
                              'uint:16=%d' % (self.source_port,
                                              self.destination_port))

        # Write the length
        payload_bytes = bytes(self.payload)
        length = len(payload_bytes) + 8
        bitstream += BitStream('uint:16=%d' % length)

        # Write the checksum
        bitstream += BitStream('uint:16=%d' % self.checksum)

        return bitstream.bytes + payload_bytes