Find an edge in an undirected graph given two edges

[David Einstein]

Given an undirected graph g, and two vertices v1 and v2 such that there is an edge connecting them, is there a simple way to figure out which one of (v1, v2) or (v2, v1) will be the edge that occurs in g.edges(labels=False)?

[Jakub Sliacan]

I thought edges are always listed sorted, i.e. x <= y in (x,y). Can you produce an example when this is not the case?

[David Einstein]

No, I cannot, but as we transfer to Python 3 it is no longer guaranteed that vertices will be sortable, and so tuple(sorted([v1,v2])) should be avoided.