code: def _op(self, _, obj, app):
          
          if obj.responses == None: return 
  
          tmp = {}
          for k, v in six.iteritems(obj.responses):
              if isinstance(k, six.integer_types):
                  tmp[str(k)] = v
              else:
                  tmp[k] = v
          obj.update_field('responses', tmp)
docs: convert status code in Responses from int to string