code: def GetNumberOfRows(self):
      
      if not self._database_object:
        raise IOError('Not opened.')
  
      if self._number_of_rows is None:
        self._number_of_rows = self._database_object.GetNumberOfRows(
            self._table_name)
  
      return self._number_of_rows
docs: Retrieves the number of rows of the table.
  
      Returns:
        int: number of rows.
  
      Raises:
        IOError: if the file-like object has not been opened.
        OSError: if the file-like object has not been opened.