code: def append(self, item: TransItem):
          
  
          if not (1 <= item.index <= settings.I18N_MAX_SENTENCES_PER_GROUP):
              return
  
          if len(self.sentences) < item.index:
              for _ in range(len(self.sentences), item.index):
                  self.sentences.append(Sentence())
  
          self.sentences[item.index - 1].append(item)
docs: Append an item to the list. If there is not enough sentences in the
          list, then the list is extended as needed.
  
          There is no control made to make sure that the key is consistent.