Graph.copy() and deepcopy

[nernst]

Hi, I found the docs a little perplexing on the subject of graph
copying.

The docs say:
Graph.copy()
"This makes a complete copy of the graph including all of the node or
edge attributes."

In the source the following is done:
return deepcopy(self)

Seems like it is doing what I wanted, but this didn't in fact return a
deepcopy. I have a Digraph with user objects on the edges and user
objects as nodes, so I ended up with copy by reference.

When I followed the forum advice, and did copy.deepcopy(G), I got the
desired result.

Perhaps the docs could reflect this fact. In particular the words
"complete copy" are confusing, it should probably reflect shallow or
deep, as desired.

[Aric Hagberg]

On Tue, Nov 10, 2009 at 9:45 AM, nernst <neil....@gmail.com> wrote:
>
> Hi, I found the docs a little perplexing on the subject of graph
> copying.
>
> The docs say:
> Graph.copy()
> "This makes a complete copy of the graph including all of the node or
> edge attributes."
>
> In the source the following is done:
> return deepcopy(self)
>
> Seems like it is doing what I wanted, but this didn't in fact return a
> deepcopy. I have a Digraph with user objects on the edges and user
> objects as nodes, so I ended up with copy by reference.
> When I followed the forum advice, and did copy.deepcopy(G), I got the
> desired result.

The intent is for Graph.copy() to make a deepcopy and as you see we
call that explicitly. I don't understand why you got something
different - but maybe I am missing something about deepcopy?
Can you provide a simple example?

>
> Perhaps the docs could reflect this fact. In particular the words
> "complete copy" are confusing, it should probably reflect shallow or
> deep, as desired.

I'll add another note to the documentation.

Aric

[Dan Schult]

Something is strange there....
If the source code uses deepcopy and you use deepcopy they
should return the same thing. Can you give a short
example that shows the shallow copy? The docs
should probably use the word "deep" instead of
"complete", but if it is actually shallow, that
is a bug. Is it possible that you are running a
different version than the source code you are
looking at? The shallow/deep choice for copy()
has changed over the versions.
Dan


This code seems to work:

class node(dict):
def __hash__(self):
return len(self)

class edge(dict):
pass

>>> G=nx.Graph()
>>> n1=node(size=1)
>>> n2=node(size=2)
>>> G.add_edge(n1,n2,edge(weight=4))
>>> H=G.copy()
>>> H[n1][n2]['color']='red'
>>> for n in H: n[2]=3
...
>>> H.adj
{{2: 3, 'size': 2}: {{2: 3, 'size': 3}: {'color': 'red', 'weight': 4}},
{2: 3, 'size': 3}: {{2: 3, 'size': 2}: {'color': 'red', 'weight': 4}}}

>>> G.adj
{{'size': 2}: {{'size': 3}: {'weight': 4}},
{'size': 3}: {{'size': 2}: {'weight': 4}}}