def _stick_device(self):
        """
        Discovers the filename of the evdev device that represents the Sense
        HAT's joystick.
        """
        for evdev in glob.glob('/sys/class/input/event*'):
            try:
                with io.open(os.path.join(evdev, 'device', 'name'), 'r') as f:
                    if f.read().strip() == self.SENSE_HAT_EVDEV_NAME:
                        return os.path.join('/dev', 'input', os.path.basename(evdev))
            except IOError as e:
                if e.errno != errno.ENOENT:
                    raise
        raise RuntimeError('unable to locate SenseHAT joystick device')
Discovers the filename of the evdev device that represents the Sense
        HAT's joystick.