code: def row_completed(self, index):
          
          self._completed_rows.append(index)
          for row_completed in self._on_row_completed:
              row_completed(index)
docs: Mark the row at index as completed.
  
          .. seealso:: :meth:`completed_row_indices`
  
          This method notifies the obsevrers from :meth:`on_row_completed`.