class_docstr: Tokenizer transform abstract class.
code: def tokenize_string(self, string, side="src", is_train=False):
      raise NotImplementedError
  
imports: import re
  from onmt.utils.logging import logger
  from onmt.transforms import register_transform
  from .transform import Transform, ObservableStats
  from onmt.constants import DefaultTokens
label_desc: Use image node_id 6 for calling the TokenizerTransform obj's underlying member method code with example usage: obj.tokenize_string(string, side, is_train) without return types