Remove the edge between vertices u and v

def remove_edge(self, u, v):
        """
        Remove the edge between vertices u and v
        """
        try:
            self.edges.pop((u, v))
        except KeyError:
            raise GraphInsertError("Edge %s-%s doesn't exist." % (u, v))
        self.vertices[u].remove(v)
        self.vertices[v].remove(u)