def number_of_interactions(G, u=None, v=None, t=None):
    """Return the number of edges between two nodes at time t.

        Parameters
        ----------
        u, v : nodes, optional (default=all edges)
            If u and v are specified, return the number of edges between
            u and v. Otherwise return the total number of all edges.
        t : snapshot id (default=None)
            If None will be returned the number of edges on the flattened graph.


        Returns
        -------
        nedges : int
            The number of edges in the graph.  If nodes u and v are specified
            return the number of edges between those nodes.

        Examples
        --------
            >>> G = dn.DynGraph()
            >>> G.add_path([0,1,2,3], t=0)
            >>> dn.number_of_interactions(G, t=0)
            """
    return G.number_of_interactions(u, v, t)
