On Aug 4, 5:21 am, Rado <rki...@gmail.com> wrote:
> Hello,
>
> (I apologize if this has been discussed and it is a design decision).
> I just noticed that graphs are passed by value instead of passed by
> reference (which i think is standard in python).
>
> example:
>
> sage:def modify(G):
> sage: G=graphs.CompleteGraph(4)
> sage:G=graphs.PetersenGraph()
> sage:modify(G)
> sage:G
> Petersen graph: Graph on 10 vertices
>
> However, a normal python behavior should be.
>
> sage:def modify_list(L):
> sage: L.append(3)
> sage:L=[1,2]
> sage:modify_list(L)
> sage:L
> [1,2,3]
>
> This can be disastrous if your are passing big graphs.
> Rado
Graphs are nothing special. Try the following:
def modify(G):
G.delete_vertex(0)
G=graphs.PetersenGraph()
modify(G)
G
In your example, you assign a different object to G, thus losing the
original reference.
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