code: def add_sent(self, sent_obj):
          ''' Add a ttl.Sentence object to this document '''
          if sent_obj is None:
              raise Exception("Sentence object cannot be None")
          elif sent_obj.ID is None:
              # if sentID is None, create a new ID
              sent_obj.ID = next(self.__idgen)
          elif self.has_id(sent_obj.ID):
              raise Exception("Sentence ID {} exists".format(sent_obj.ID))
          self.__sent_map[sent_obj.ID] = sent_obj
          self.__sents.append(sent_obj)
          return sent_obf add_sent(self, sent_obj):
          ''' Add a ttl.Sentence object to this document '''
          if sent_obj is None:
              raise Exception("Sentence object cannot be None")
          elif sent_obj.ID is None:
              # if sentID is None, create a new ID
              sent_obj.ID = next(self.__idgen)
          elif self.has_id(sent_obj.ID):
              raise Exception("Sentence ID {} exists".format(sent_obj.ID))
          self.__sent_map[sent_obj.ID] = sent_obj
          self.__sents.append(sent_obj)
          return sent_obj
docs: Add a ttl.Sentence object to this document