def __missing__(self, key):
        if self.default_factory is None:
            raise KeyError(key)
        else:
            ret = self[key] = self.default_factory(name=key)
            return ret
def animate_cluster_allocation(data, observer, animation_velocity = 75, movie_fps = 1, save_movie = None):
        """!
        @brief Animates clustering process that is performed by EM algorithm.