<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def bars(self):
 """A string of the bar and space weights of the barcode. Starting with a bar and alternating. '2112142311131122142211142211141341112221221212412331112' :rtype: string """

        return ''.join(map((lambda val: self._val2bars[val]), self.symbol_values))