code: def _process_batch(self, param, df_name):
          
          if param.eval_metric is not None:
              metrics = dict(param.eval_metric.get_name_value())
              param.eval_metric.reset()
          else:
              metrics = {}
          metrics['elapsed'] = datetime.datetime.now() - self.start_time
          for key, value in metrics.items():
              if key not in self._data[df_name]:
                  self._data[df_name][key] = []
              self._data[df_name][key].append(value)
docs: Update selected dataframe after a completed batch
          Parameters
          ----------
          df_name : str
              Selected dataframe name needs to be modified.