def on_cleanup_error(function, path, excinfo):
                click.secho("warning: failed to remove file or directory: {}\n"
                            "please delete it manually.".format(path),
                            fg="red")
def get_evolution_covariances(self):
        """!
        @return (list) Covariance matrix (or variance in case of one-dimensional data) of each cluster on each step of clustering.