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 notify(self, means, covariances, clusters):
        """!
        @brief This method is used by the algorithm to notify observer about changes where the algorithm
                should provide new values: means, covariances and allocated clusters.