code: def snake(self, duration: float = 0.03):
          
          for button in BUTTONS:
              self.light_on(button)
              time.sleep(duration)
  
          for button in reversed(BUTTONS):
              self.light_off(button)
              time.sleep(duration)
docs: Turn the button lights on then off in a snakelike sequence.
          NOTE! Does not remember prior state of lights and will finish
          with all lights off.
          :param duration: The duration to hold each individual button.