How can I sort a django request set for a total of two fields?

I want to annotate a list of objects (each of which has a set tagsand an integer value points) so that they can be sorted by the total number of tags plus points.

However, I cannot find a way to annotate objects with the sum of two columns. Any idea on how I should do this?

These are the models that I use, and the function leaderboard()is the one with which I have difficulty working.

class Game (models.Model):
    users = models.ManyToManyField(User, through='Player', related_name='games')

    def leaderboard (self):
        """ Return a list of players ranked by score, where score is the total of the count of the players tags and their points. """
        leaderboard = self.player_set.annotate(
            tagcount=models.Count('tags')
        ).extra(
            select={'score': 'tagcount + points'},
            order_by=('score',)
        )
        return leaderboard

class Player (models.Model):
    game = models.ForeignKey(Game)
    user = models.ForeignKey(User)
    points = models.SmallIntegerField(default=0, help_text="Points that have been awarded to the player")

class Tag (models.Model):
    game = models.ForeignKey(Game, related_name='tags')
    player = ForeignKey(Player, related_name='tags')

Edit 2: Solution Using Extra

Ok, so I had to work extra by manually counting the number of tags and adding them to the points.

def leaderboard (self):
    """ Return a list of players ranked by score, where score is the total of the count of the players tags and their points. """
    return self.players.extra(
        select={'score': '(select count(*) from kaos_tag where kaos_tag.tagger_id=kaos_player.id) + points'},
        order_by=('-score',)
    )