def interactions_per_snapshots(G, t=None):
    """Return the number of interactions within snapshot t.

        Parameters
        ----------

        G : graph
            A DyNetx graph.

        t : snapshot id (default=None)
            If None will be returned total number of interactions across all snapshots

        Returns
        -------

        nd : dictionary, or number
            A dictionary with snapshot ids as keys and interaction count as values or
            a number if a single snapshot id is specified.

        Examples
        --------
        >>> G = dn.DynGraph()
        >>> G.add_path([0,1,2,3], t=0)
        >>> G.add_path([0,4,5,6], t=1)
        >>> G.add_path([7,1,2,3], t=2)
        >>> dn.number_of_interactions(G, t=0)
        3
        >>> dn.interactions_per_snapshots(G)
        {0: 3, 1: 3, 2: 3}
        """
    return G.interactions_per_snapshots(t)