code: def value(self):
          
          result = sum(led.value for led in self)
          if self[0].value < self[-1].value:
              result = -result
          return result / len(self)
docs: The value of the LED bar graph. When no LEDs are lit, the value is 0.
          When all LEDs are lit, the value is 1. Values between 0 and 1
          light LEDs linearly from first to last. Values between 0 and -1
          light LEDs linearly from last to first.
  
          To light a particular number of LEDs, simply divide that number by
          the number of LEDs. For example, if your graph contains 3 LEDs, the
          following will light the first::
  
              from gpiozero import LEDBarGraph
  
              graph = LEDBarGraph(12, 16, 19)
              graph.value = 1/3
  
          .. note::
  
              Setting value to -1 will light all LEDs. However, querying it
              subsequently will return 1 as both representations are the same in
              hardware. The readable range of :attr:`value` is effectively
              -1 < value <= 1.