def fractionally_isomorphic_graphs(graph):
    """Returns an iterator over all graphs that are fractionally isomorphic to
    the specified graph, including the graph itself.

    `graph` must be an instance of :class:`networkx.Graph`.

    .. warning::

       This function is currently not implemented, since it is very difficult
       to write correct code that enumerates each graph that is fractionally
       isomorphic to a given graph (that is, it seems that the code will be
       very complicated).

    """
    raise NotImplementedError
