code: def append(self, data_frame):
          
          if len(data_frame) == 0:  # empty DataFrame, do nothing
              return
          data_frame_index = data_frame.index
          combined_index = self._index + data_frame_index
          if len(set(combined_index)) != len(combined_index):
              raise ValueError('duplicate indexes in DataFrames')
  
          for c, column in enumerate(data_frame.columns):
              if PYTHON3:
                  self.set(indexes=data_frame_index, columns=column, values=data_frame.data[c].copy())
              else:
                  self.set(indexes=data_frame_index, columns=column, values=data_frame.data[c][:])
docs: Append another DataFrame to this DataFrame. If the new data_frame has columns that are not in the current
          DataFrame then new columns will be created. All of the indexes in the data_frame must be different from the
          current indexes or will raise an error.
  
          :param data_frame: DataFrame to append
          :return: nothing