code: def kernel_comm_word_string(
      fm_train_dna=traindat,
      fm_test_dna=testdat,
      order=3,
      gap=0,
      reverse=False,
      use_sign=False,
  ):
      charfeat = sg.create_string_features(fm_train_dna, sg.DNA)
      feats_train = sg.create_string_features(
          charfeat, order - 1, order, gap, reverse
      )
      preproc = sg.create_transformer("SortWordString")
      preproc.fit(feats_train)
      feats_train = preproc.transform(feats_train)
  
      charfeat = sg.create_string_features(fm_test_dna, sg.DNA)
      feats_test = sg.create_string_features(
          charfeat, order - 1, order, gap, reverse
      )
      feats_test = preproc.transform(feats_test)
  
      kernel = sg.create_kernel(
          "CommWordStringKernel", use_sign=use_sign
      )
      kernel.init(feats_train, feats_train)
  
      km_train = kernel.get_kernel_matrix()
      kernel.init(feats_train, feats_test)
      km_test = kernel.get_kernel_matrix()
      return km_train, km_test, kernel
  
label_desc: Use image node_id 1 for calling a global function with example usage: kernel_comm_word_string(fm_train_dna, fm_test_dna, order, gap, reverse, use_sign) and returns: km_train,  km_test,  kernel