有什么办法可以从python networkx的边缘查找所有唯一属性？

Question

G.add_edges_from([('c1','C'),('c2','C'),('c3','C'),('c4','C')], label= 'type')            
G.add_edges_from([('c1','e1'),('c2','e1'),('c3','e1'),('c4','e1')], label = 'p1')
G.add_edges_from([('c1','e2'),('c2','e2'),('c3','e2'),('c4','e2')], label = 'p2')
G.add_edges_from([('c1','e3'),('c2','e3'),('c3','e3'),('c4','e3')], label = 'p3')
G.add_edges_from([('c1','e4'),('c2','e4'),('c3','e5'),('c4','e6')], label = 'p4')

列表的边缘有4个不同的标签， 如何只在一个列表中获得标签？