code: def _prepare_reserved_tokens(reserved_tokens):
    
    reserved_tokens = [tf.compat.as_text(tok) for tok in reserved_tokens or []]
    dups = _find_duplicates(reserved_tokens)
    if dups:
      raise ValueError("Duplicates found in tokens: %s" % dups)
    reserved_tokens_re = _make_reserved_tokens_re(reserved_tokens)
    return reserved_tokens, reserved_tokens_re
docs: Prepare reserved tokens and a regex for splitting them out of strings.