code: def _add_column(self, column):
          
          self._columns.append(column)
          if self._blist:
              self._data.append(blist([None] * len(self._index)))
          else:
              self._data.append([None] * len(self._index))
docs: Add a new column to the DataFrame
  
          :param column: column name
          :return: nothing