docs: def bars(self):
          """A string of the bar and space weights of the barcode. Starting with a bar and alternating.
  
          >>> barcode = Code128("Hello!", charset='B')
          >>> barcode.bars
          '2112142311131122142211142211141341112221221212412331112'
  
          :rtype: string
          """
          return ''.join(map((lambda val: self._val2bars[val]), self.symbol_values))