code: def add(self, response, label=None):
          
          if not isinstance(response, sip_response.sip_response):
              raise Exception(
                  'can only add sip_reponse.sip_response objects'
              )
          self.objects.append(response)
  
          if label is None:
              self.labels.append('na')
          else:
              self.labels.append(label)
docs: add one response object to the list