(Python graph-tool)使用graph-tool查找特定长度的路径？

import graph_tool.all as gt

# 创建一个有向图
g = gt.Graph(directed=True)

# 添加节点
v1 = g.add_vertex()
v2 = g.add_vertex()
v3 = g.add_vertex()
v4 = g.add_vertex()

# 添加边
e1 = g.add_edge(v1, v2)
e2 = g.add_edge(v2, v3)
e3 = g.add_edge(v3, v4)
e4 = g.add_edge(v1, v3)
e5 = g.add_edge(v2, v4)

# 查找长度为3的路径
paths = gt.topology.all_paths(g, v1, v4, cutoff=3)

# 打印路径
for path in paths:
    print(path)