creating a graph from a graph with one edge removed

[Ken Levasseur]

I want to examine graphs I get by removing single edges from an initial graph and I've run into a problem.  Here it is:

For example, I start with 

c6=graphs.CycleGraph(6)

a=c6.edges()[0]

p6=c6

p6.delete_edge(a)

Now if I do this:

p6.is_tree()

I get the output I expect,  True.

However, if evaluate the following, I also get True

c6.is_tree()

Removing the edge from p6 also removes it from c6.  So p6 and c6 seem to be pointers to the same structure.  How do I create a truely new graph out of the original?

Ken Levasseur

UMass Lowell 

[Christophe Bal]

Hello.

This is certainly due to the way Python manages unhashable variables. If you type p6 is c6, you will obtain True, in other words, p6 and c6 are two references to the same object.

Using p6=c6.copy() will do the job.

Best regards.

Christophe BAL

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[Ken Levasseur]

Christophe:

Thank you, I suspected that there must have been a method like copy, but didn't know what it was.

Ken