def _canonicalize_hostname(hn):
    """
        A canonicalized host name is the string generated by the following algorithm:
            1.  Convert the host name to a sequence of individual domain name labels.
            2.  Convert each label that is not a Non-Reserved LDH (NR-LDH) label,
                to an A-label (see Section 2.3.2.1 of [RFC5890] for the former and latter), 
                or to a "punycode label" (a label resulting from the "ToASCII" conversion in Section 4 of [RFC3490]), 
                as appropriate (see Section 6.3 of this specification).
            3.  Concatenate the resulting labels, separated by a %x2E (".") character.
    """
    print('NOT IMPLEMENTED YET')
    return hn
