def make_patch(self):
        '''Currently only works if all the pieces are Arcgons.
           In this case returns a multiple-piece path. Otherwise throws an exception.'''
        paths = [p.make_patch().get_path() for p in self.pieces]
        vertices = np.concatenate([p.vertices for p in paths])
        codes = np.concatenate([p.codes for p in paths])
        return PathPatch(Path(vertices, codes))
Currently only works if all the pieces are Arcgons.
           In this case returns a multiple-piece path. Otherwise throws an exception.