title: List of edges that don't exist in a networkx graph?
body: <p>I have a <code>networkx</code> graph. With <code>G.edges()</code> I can get a list of all the edges. But is there a way to get a list of all other non-existing edges? So if there are 3 nodes: a, b, c and we suppose a and b are connected only, then I would like to get a list of edges that don't exist, so like this: <code>(a,c), (c,b)</code>. Is there an easy pythonic way to do this?</p>