code: def hashret(self):
          
          if 'PositiveResponse' in self.services[self.service]:
              return struct.pack('B', self.service - 0x40)
          elif self.service == 0x7f:
              return struct.pack('B', self.requestServiceId)
          else:
              return struct.pack('B', self.service)
docs: DEV: returns a string that has the same value for a request and its answer.