def _splitnport(host, defport=-1):
    """Split host and port, returning numeric port.
    Return given default port if no ':' found; defaults to -1.
    Return numerical port if a valid number are found after ':'.
    Return None if ':' but not a valid number."""
    host, delim, port = host.rpartition(':')
    if not delim:
        host = port
    elif port:
        try:
            nport = int(port)
        except ValueError:
            nport = None
        return host, nport
    return host, defport