def _is_control(char):
    """Checks whether `chars` is a control character."""
    # These are technically control characters but we count them as whitespace
    # characters.
    if char == '\t' or char == '\n' or char == '\r':
        return False
    cat = unicodedata.category(char)
    if cat in ('Cc', 'Cf'):
        return True
    return False
Checks whether `chars` is a control character.
bert_tokenizer.py