code: def hash_prefix_list_checksum(self, threat_list):
          q = '''SELECT value FROM hash_prefix
                  WHERE threat_type=? AND platform_type=? AND threat_entry_type=?
                  ORDER BY value
          '''
          params = [threat_list.threat_type, threat_list.platform_type, threat_list.threat_entry_type]
          with self.get_cursor() as dbc:
              dbc.execute(q, params)
              all_hashes = b''.join(bytes(h[0]) for h in dbc.fetchall())
              checksum = hashlib.sha256(all_hashes).digest()
          return checksum