code: def append_metrics(self, metrics, df_name):
          
          dataframe = self._dataframes[df_name]
          _add_new_columns(dataframe, metrics)
          dataframe.loc[len(dataframe)] = metrics
docs: Append new metrics to selected dataframes.
  
          Parameters
          ----------
          metrics : metric.EvalMetric
              New metrics to be added.
          df_name : str
              Name of the dataframe to be modified.