code: def normalize_text(text: str) -> str:
      
      return ' '.join([token
                       for token in text.lower().strip(STRIPPED_CHARACTERS).split()
                       if token not in IGNORED_TOKENS])
docs: Performs a normalization that is very similar to that done by the normalization functions in
      SQuAD and TriviaQA.
  
      This involves splitting and rejoining the text, and could be a somewhat expensive operation.