[igraph] Save vertex property

[Николай Кинаш]

Hello

>>> graph = ig.Graph()

>>> graph.add_vertex()

>>> graph.vs[0]["age"] = 55

>>> graph.vs[0]["age"]

55

>>> graph = ig.Graph().Barabasi(graph.vcount()+3, 3, power=2.5, start_from=graph, outpref=True)

>>> graph.vs[0]["age"]

Traceback (most recent call last):

  File "<stdin>", line 1, in <module>

KeyError: 'Attribute does not exist'

It is possible to save "age" property after ig.Graph().Barabasi ?

Thanks.