deeper graph

def to_deeper_graph(graph):
    ''' deeper graph
    '''

    weighted_layer_ids = graph.deep_layer_ids()
    if len(weighted_layer_ids) >= Constant.MAX_LAYERS:
        return None

    deeper_layer_ids = sample(weighted_layer_ids, 1)

    for layer_id in deeper_layer_ids:
        layer = graph.layer_list[layer_id]
        new_layer = create_new_layer(layer, graph.n_dim)
        graph.to_deeper_model(layer_id, new_layer)
    return graph