code: def unk_id(self):
      return self.unknown_id
  
imports: import itertools
  import math
  from typing import Iterable, List, Optional, Tuple, Union
  import numpy
  import torch
  from nemo.collections.common.tokenizers.tokenizer_spec import TokenizerSpec
  from nemo.core.classes import NeuralModule, typecheck
  from nemo.core.neural_types import LengthsType, LogprobsType, NeuralType, PredictionsType
label_desc: Use image node_id 3 for calling the _TokensWrapper obj's underlying member method code with example usage: obj.unk_id() and returns: self