docs: def _findRow(subNo, model):
      """Finds a row in a given model which has a column with a given
      number."""
      items = model.findItems(str(subNo))
      if len(items) == 0:
          return None
      if len(items) > 1:
          raise IndexError("Too many items with sub number %s" % subNo)
      return items[0].row()