Set attributes for each LED in group.

        Example::

            my_leds = Leds()
            my_leds.set_color('LEFT', brightness_pct=0.5, trigger='timer')

def set(self, group, **kwargs):
        """
        Set attributes for each LED in group.

        Example::

            my_leds = Leds()
            my_leds.set_color('LEFT', brightness_pct=0.5, trigger='timer')
        """

        # If this is a platform without LEDs there is nothing to do
        if not self.leds:
            return

        assert group in self.led_groups, \
            "%s is an invalid LED group, valid choices are %s" % \
            (group, ', '.join(self.led_groups.keys()))

        for led in self.led_groups[group]:
            for k in kwargs:
                setattr(led, k, kwargs[k])