Get a kitten, either from the db, or a new one.

def get_random(self):
        """Get a kitten, either from the db, or a new one.
        """
        num_kittens = self.count()
        new_cutoff = (num_kittens / (num_kittens + constants.KITTEN_FRESHNESS))
        if random.random() < new_cutoff:
            return self._rand_inst()
        else:
            return self.create_new()