def nodes(G, t=None):
    """Return a list of the nodes in the graph at a given snapshot.

            Parameters
            ----------

            G : Graph opject
                DyNetx graph object

            t : snapshot id (default=None)
                If None the the method returns all the nodes of the flattened graph.

            Returns
            -------
            nlist : list
                A list of nodes.  If data=True a list of two-tuples containing
                (node, node data dictionary).

            Examples
            --------
            >>> G = dn.DynGraph()   # or DiGraph, MultiGraph, MultiDiGraph, etc
            >>> G.add_path([0,1,2], 0)
            >>> dn.nodes(G, t=0)
            [0, 1, 2]
            >>> G.add_edge(1, 4, t=1)
            >>> dn.nodes(G, t=0)
            [0, 1, 2]
            """
    return G.nodes(t)