'Returns the user\'s default drone set, if present.
Otherwise, returns the global default drone set.'

def _user_or_global_default_drone_set(self, obj_with_owner, user):

    default_hostnames = models.DroneSet.get_default().get_drone_hostnames()
    if (not user):
        logging.warn('%s    had    no    owner;    using    default    drone    set', obj_with_owner)
        return default_hostnames
    if (not user.drone_set):
        logging.warn('User    %s    has    no    default    drone    set,    using    global    default', user.login)
        return default_hostnames
    return user.drone_set.get_drone_hostnames()
