def get_story_memcache_key(story_id, version=None):
    """Returns a memcache key for the story.

    Args:
        story_id: str. ID of the story.
        version: str. Schema version of the story.

    Returns:
        str. The memcache key of the story.
    """
    if version:
        return 'story-version:%s:%s' % (story_id, version)
    else:
        return 'story:%s' % story_id