Return a Powernode object describing the given powernode

def powernode_data(self, name:str) -> Powernode:
        """Return a Powernode object describing the given powernode"""
        self.assert_powernode(name)
        contained_nodes = frozenset(self.nodes_in(name))
        return Powernode(
            size=len(contained_nodes),
            contained=frozenset(self.all_in(name)),
            contained_pnodes=frozenset(self.powernodes_in(name)),
            contained_nodes=contained_nodes,
        )