def METHOD_NAME(self):
    """
    Returns:
        int: Number of empty slots in queue
    Pages:
        in: is_in_queue
    """
    status = [self._queue_status_detect(button) for button in self.queue_status_grids.buttons]
    logger.info(f'Research queue: {status}')
    status = status[::-1]
    for index, s in enumerate(status):
        if s != 'empty':
            logger.attr('Research queue slot', index)
            return index
    index = len(status)
    logger.attr('Research queue slot', index)
    return index