Iterating FSTs

In this tutorial, we demonstrate how to iterate the states and arcs of an FST.

We use the binary.fst generated in Creating FSTs using constructors and mutators as an example.

Fig. 3 binary.fst from Creating FSTs using constructors and mutators.

We will change it to the following FST:

Fig. 4 FST generated by this section by changing binary.fst. Note that we change the weight of each arc.

Listing 3 Iterating an FST

#!/usr/bin/env python3

import graphviz

import kaldifst


def main():
    fst = kaldifst.StdVectorFst.read("binary.fst")
    for state in kaldifst.StateIterator(fst):
        for arc in kaldifst.ArcIterator(fst, state):

            # Note: We can change the attribute of the arc if we want
            if arc.weight == 0.5:
                arc.weight = 0.6
            elif arc.weight == 1.5:
                arc.weight = 1.8
            elif arc.weight == 2.5:
                arc.weight = 1.25

            print(state, arc)

    fst_dot = kaldifst.draw(fst, acceptor=False, portrait=True)
    source = graphviz.Source(fst_dot)
    source.render(outfile="quick-start-3.svg")


if __name__ == "__main__":
    main()
"""
Output of this file:

0 (ilabel: 1, olabel: 1, weight: 0.6, nextstate: 1)
0 (ilabel: 2, olabel: 2, weight: 1.8, nextstate: 1)
1 (ilabel: 3, olabel: 3, weight: 1.25, nextstate: 2)
"""