class_docstr: Base class inherited by all tokenizer classes. This class
  handles downloading and loading pre-trained tokenizer and adding tokens to
  the vocabulary.
  
  Derived class can set up a few special tokens to be used in common scripts
  and internals: :attr:`bos_token`, :attr:`eos_token`, :attr:`unk_token`,
  :attr:`sep_token`, :attr:`pad_token`, :attr:`cls_token`,
  :attr:`mask_token`, and :attr:`additional_special_tokens`.
  
  We defined an :attr:`added_tokens_encoder` to add new tokens to the
  vocabulary without having to handle the specific vocabulary augmentation
  methods of the various underlying dictionary structures (`BPE`,
  `sentencepiece` ...).
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code: def _map_id_to_token(self, token_id: int) -> str:
      raise NotImplementedError
  
imports: from typing import Any, Dict, List, Optional, Tuple, overload
  import json
  import os
  import warnings
  from texar.tf.module_base import ModuleBase
label_desc: Use image node_id 20 for calling the TokenizerBase obj's underlying member method code with example usage: obj._map_id_to_token(token_id) without return types