def names2dnsrepr(x):
    """
    Take as input a list of DNS names or a single DNS name
    and encode it in DNS format (with possible compression)
    If a string that is already a DNS name in DNS format
    is passed, it is returned unmodified. Result is a string.
    !!!  At the moment, compression is not implemented  !!!
    """

    if isinstance(x, bytes):
        if x and x[-1:] == b'\x00':  # stupid heuristic
            return x
        x = [x]

    res = []
    for n in x:
        termin = b"\x00"
        if n.count(b'.') == 0:  # single-component gets one more
            termin += b'\x00'
        n = b"".join(chb(len(y)) + y for y in n.split(b'.')) + termin
        res.append(n)
    return b"".join(res)