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.

def set_backlight(self, backlight):
        """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.
        """
        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)