How to use the smt.ibmmodel.ibmmodel2.viterbi_alignment function in smt

def test_viterbi_alignment(self):
        x = viterbi_alignment([1, 2, 1],
                              [2, 3, 2],
                              collections.defaultdict(int),
                              collections.defaultdict(int))
        # Viterbi_alignment selects the first token
        # if t or a doesn't contain the key.
        # This means it returns NULL token
        # in such a situation.
        self.assertEqual(x, {1: 1, 2: 1, 3: 1})

def symmetrization(es, fs, corpus):
    '''
    forpus
        for translation from fs to es
    return
        alignment **from fs to es**
    '''
    f2e_train = ibmmodel2._train(corpus, loop_count=10)
    f2e = ibmmodel2.viterbi_alignment(es, fs, *f2e_train).items()

    e2f_corpus = list(zip(*reversed(list(zip(*corpus)))))
    e2f_train = ibmmodel2._train(e2f_corpus, loop_count=10)
    e2f = ibmmodel2.viterbi_alignment(fs, es, *e2f_train).items()

    return alignment(es, fs, e2f, f2e)

def symmetrization(es, fs, corpus):
    '''
    forpus
        for translation from fs to es
    return
        alignment **from fs to es**
    '''
    f2e_train = ibmmodel2._train(corpus, loop_count=10)
    f2e = ibmmodel2.viterbi_alignment(es, fs, *f2e_train).items()

    e2f_corpus = list(zip(*reversed(list(zip(*corpus)))))
    e2f_train = ibmmodel2._train(e2f_corpus, loop_count=10)
    e2f = ibmmodel2.viterbi_alignment(fs, es, *e2f_train).items()

    return alignment(es, fs, e2f, f2e)