def label_isolated(g):
    """label_isolated
    Creates a vertex property map with True if a node has no neighbours,
    else False.

    Parameters
    ----------
        g (graph_tool.Graph):
            A graph.

    Returns
    -------
        isolated_vp (graph_tool.VertexPropertyMap):
            Property map labelling isolated vertices.
    """
    isolated_vp = g.new_vertex_property('bool')
    for v in g.vertices():
        if v.out_degree() == 0:
            isolated_vp[v] = True
        else:
            isolated_vp[v] = False
    return isolated_vp