def METHOD_NAME(self):
    """
    Returns the extended Dynkin diagram for type G.
    EXAMPLES::
        sage: g = CartanType(['G',2,1]).dynkin_diagram(); g                         # needs sage.graphs
          3
        O=<=O---O
        1   2   0
        G2~
        sage: g.edges(sort=True)                                                    # needs sage.graphs
        [(0, 2, 1), (1, 2, 1), (2, 0, 1), (2, 1, 3)]
    """
    from .METHOD_NAME import DynkinDiagram_class
    g = DynkinDiagram_class(self)
    g.add_edge(1, 2)
    g.set_edge_label(2,1,3)
    g.add_edge(0, 2)
    return g