code: def transform(self, input_: list) -> list:
      """
      Transform token into tri-letter.
  
      For example, `word` should be represented as `#wo`,
      `wor`, `ord` and `rd#`.
  
      :param input_: list of tokens to be transformed.
  
      :return n_letters: generated n_letters.
      """
      n_letters = []
      for token in input_:
          token = "#" + token + "#"
          token_ngram = []
          while len(token) >= self._ngram:
              token_ngram.append(token[: self._ngram])
              token = token[1:]
          if self._reduce_dim:
              n_letters.extend(token_ngram)
          else:
              n_letters.append(token_ngram)
      return n_letters
  
imports: from .unit import Unit
label_desc: Use image node_id 2 for calling the NgramLetter obj's underlying member method code with example usage: obj.transform(input_) and returns: n_letters