code: def symmetrization(es, fs, f2e_train, e2f_train):
      '''
      forpus
          for translation from fs to es
      return
          alignment **from fs to es**
      '''
      f2e = viterbi_alignment(es, fs, *f2e_train).items()
      e2f = viterbi_alignment(fs, es, *e2f_train).items()
      
      
      _e2f = list(zip(*reversed(list(zip(*e2f)))))
      return _alignment(es, fs, _e2f, f2e)
docs: forpus
          for translation from fs to es
      return
          alignment **from fs to es**