Graph.num_edges() gives wrong answer

[sagetrac-tobiasljohnson]

If G is a graph with multiedges that contains two copies of an edge e, and you delete one of the copies, num_edges() doesn't go down by one. For example,

sage: G = Graph(multiedges = True)
sage: G.add_edges([(0,1), (0,1)])
sage: G.delete_edge(0,1)
sage: G.num_edges()
2
sage: G.edges()
[(0, 1, None)]

Component: graph theory

Keywords: num_edges, multiedges

Reviewer: Minh Van Nguyen

Issue created by migration from https://trac.sagemath.org/ticket/9809

[sagetrac-mvngu]

comment:2

The problem is fixed at #8395.

[jdemeyer]

Reviewer: Minh Van Nguyen