def register(self, device, callback):
if not device:<EOL><INDENT>logger.error("<STR_LIT>", device)<EOL>return<EOL><DEDENT>logger.debug("<STR_LIT>", device.name)<EOL>self._devices[device.vera_device_id].append(device)<EOL>self._callbacks[device].append(callback)<EOL>
Register a callback.

        device: device to be updated by subscription
        callback: callback for notification of changes