code: def set_backlight(self, backlight):
          
          if self._backlight is not None:
              if self._pwm_enabled:
                  self._backlight.pwm_start(self._pwm_duty_cycle(backlight))
              else:
                  self._backlight.set(self._blpol if backlight else not self._blpol)
docs: Enable or disable the backlight.  If PWM is not enabled (default), a
          non-zero backlight value will turn on the backlight and a zero value will
          turn it off.  If PWM is enabled, backlight can be any value from 0.0 to
          1.0, with 1.0 being full intensity backlight.