def checksum(self):
        """ Prior to v2 format CRC was contained in every message. This will
            be the checksum for v0 and v1 and None for v2 and above.
        """
 Prior to v2 format CRC was contained in every message. This will
            be the checksum for v0 and v1 and None for v2 and above.
        
kafka/record/abc.py