code: def save_feature_names(self, feature_names, feature_list_id):
          
  
          save_lines(feature_names, self.features_dir + 'X_train_{}.names'.format(feature_list_id))
docs: Save the names of the features for the given feature list to a metadata file.
          Example: `save_feature_names(['num_employees', 'stock_price'], 'company')`.
  
          Args:
              feature_names: A list containing the names of the features, matching the column order.
              feature_list_id: The name for this feature list.