def set_edge_label(self, edge, label):
        """
        Set the label of an edge.

        @type  edge: edge
        @param edge: One edge.

        @type  label: string
        @param label: Edge label.
        """
        self.set_edge_properties(edge, label=label )
        if not self.DIRECTED:
            self.set_edge_properties((edge[1], edge[0]) , label=label )
Set the label of an edge.

        @type  edge: edge
        @param edge: One edge.

        @type  label: string
        @param label: Edge label.