import fst

t = fst.Transducer()

t.add_arc(0, 1, 'a', 'A', 0.5)
t.add_arc(0, 1, 'b', 'B', 1.5)
t.add_arc(1, 2, 'c', 'C', 2.5)

t[2].final = 3.5

t

t.shortest_path()