Returns a set of all unassigned ports (according to IANA and Wikipedia)

def _unassigned_ports():
    """ Returns a set of all unassigned ports (according to IANA and Wikipedia) """
    free_ports = ranges_to_set(_parse_ranges(_iana_unassigned_port_ranges()))
    known_ports = ranges_to_set(_wikipedia_known_port_ranges())
    return free_ports.difference(known_ports)