Returns the number of rows.

        Returns
        -------
        out : int
            Number of rows in the SFrame.

def num_rows(self):
        """
        Returns the number of rows.

        Returns
        -------
        out : int
            Number of rows in the SFrame.
        """
        if self._is_vertex_frame():
            return self.__graph__.summary()['num_vertices']
        elif self._is_edge_frame():
            return self.__graph__.summary()['num_edges']