Creating FSTs using constructors and mutators
In this tutorial, we demonstrate how to create the following FST using constructors and mutators from Python.
Fig. 1 quick-start.svg
1#!/usr/bin/env python3
2
3import graphviz
4
5import kaldifst
6
7
8def main():
9 # A vector FST is a general mutable FST
10 fst = kaldifst.StdVectorFst()
11
12 # Adds state 0 to the initially empty FST and make it the start state.
13 s0 = fst.add_state() # 1st state will be state 0 (returned by add_state)
14 assert s0 == 0
15 fst.start = 0 # set the start state to 0
16
17 # Adds two arcs exiting state 0.
18 # Arc constructor args: ilabel, olabel, weight, dest state ID.
19 fst.add_arc(
20 state=0,
21 arc=kaldifst.StdArc(ilabel=1, olabel=1, weight=0.5, nextstate=1),
22 )
23
24 fst.add_arc(
25 state=0,
26 arc=kaldifst.StdArc(ilabel=2, olabel=2, weight=1.5, nextstate=1),
27 )
28
29 # Adds state 1 and its arc.
30 fst.add_state()
31 fst.add_arc(
32 state=1,
33 arc=kaldifst.StdArc(ilabel=3, olabel=3, weight=2.5, nextstate=2),
34 )
35
36 # Adds state 2 and set its final weight.
37 fst.add_state()
38 fst.set_final(state=2, weight=3.5) # 1st arg is state ID, 2nd arg weight
39
40 # Add an input symbol table
41 isym = kaldifst.SymbolTable()
42 isym.add_symbol(symbol="a", key=1)
43 isym.add_symbol("b", 2)
44 isym.add_symbol("c", 3)
45 fst.input_symbols = isym
46
47 # Add an output symbol table
48 osym = kaldifst.SymbolTable()
49 osym.add_symbol("x", 1)
50 osym.add_symbol("y", 2)
51 osym.add_symbol("z", 3)
52 fst.output_symbols = osym
53
54 # We can save this FST to a file with
55 fst.write(filename="binary.fst")
56
57 # We can read it back
58 fst2 = kaldifst.StdVectorFst.read("binary.fst")
59 print(fst2)
60 print(fst2.to_str())
61
62 # Get a dot format of the FST for visualization
63 fst_dot = kaldifst.draw(fst, acceptor=False, portrait=True)
64 print(fst_dot)
65 # You can use
66 # https://dreampuf.github.io/GraphvizOnline
67 # to visualize it and share the link to others
68
69 # Alternatively, you can use graphviz to visualize it
70 source = graphviz.Source(fst_dot)
71 source.render(outfile="quick-start.svg")
72 # Done. quick-start.svg is the figure we showed at the start of this section
73
74
75if __name__ == "__main__":
76 main()