code: def mean_absolute_percentage_error(df, col_true, col_pred=None):
      
      if not col_pred:
          col_pred = get_field_name_by_role(df, FieldRole.PREDICTED_VALUE)
      return _run_evaluation_node(df, col_true, col_pred)['mape']
docs: Compute mean absolute percentage error of a predicted DataFrame.
  
      Note that this method will trigger the defined flow to execute.
  
      :param df: predicted data frame
      :type df: DataFrame
      :param col_true: column name of true value
      :type col_true: str
      :param col_true: column name of predicted value, 'prediction_score' by default.
      :type col_pred: str
      :return: Mean absolute percentage error
      :rtype: float