'Find all queues matching `routing_key` for the given `exchange`.
Returns:
str: queue name -- must return the string `default`
if no queues matched.'

def _lookup(self, exchange, routing_key, default=None):

    if (default is None):
        default = self.deadletter_queue
    if (not exchange):
        return [(routing_key or default)]
    try:
        R = self.typeof(exchange).lookup(self.get_table(exchange), exchange, routing_key, default)
    except KeyError:
        R = []
    if ((not R) and (default is not None)):
        warnings.warn(UndeliverableWarning(UNDELIVERABLE_FMT.format(exchange=exchange, routing_key=routing_key)))
        self._new_queue(default)
        R = [default]
    return R
