code: def _prepend_row_index(rows, index):
      
      if index is None or index is False:
          return rows
      if len(index) != len(rows):
          print('index=', index)
          print('rows=', rows)
          raise ValueError('index must be as long as the number of data rows')
      rows = [[v] + list(row) for v, row in zip(index, rows)]
      return rows
docs: Add a left-most index column.