How to use the queuelib.PriorityQueue function in queuelib

def open(self, spider):
        self.spider = spider
        self.mqs = PriorityQueue(self._newmq)
        self.dqs = self._dq() if self.dqdir else None
        return self.df.open()

def _dq(self):
        activef = join(self.dqdir, 'active.json')
        if exists(activef):
            with open(activef) as f:
                prios = json.load(f)
        else:
            prios = ()
        q = PriorityQueue(self._newdq, startprios=prios)
        if q:
            log.msg(format="Resuming crawl (%(queuesize)d requests scheduled)",
                    spider=self.spider, queuesize=len(q))
        return q

if slot not in self.pqueues:
            self.pqueues[slot] = self.pqfactory()
        queue = self.pqueues[slot]
        queue.push(obj, priority)

    def close(self):
        active = {slot: queue.close()
                  for slot, queue in self.pqueues.items()}
        self.pqueues.clear()
        return active

    def __len__(self):
        return sum(len(x) for x in self.pqueues.values()) if self.pqueues else 0


class ScrapyPriorityQueue(PriorityQueue):
    """
    PriorityQueue which works with scrapy.Request instances and
    can optionally convert them to/from dicts before/after putting to a queue.
    """
    def __init__(self, crawler, qfactory, startprios=(), serialize=False):
        super(ScrapyPriorityQueue, self).__init__(qfactory, startprios)
        self.serialize = serialize
        self.spider = crawler.spider

    @classmethod
    def from_crawler(cls, crawler, qfactory, startprios=(), serialize=False):
        return cls(crawler, qfactory, startprios, serialize)

    def push(self, request, priority=0):
        if self.serialize:
            request = request_to_dict(request, self.spider)

def __init__(self, settings):
        self.settings = settings
        self.mq_class = load_object(settings['SCHEDULER_MEMORY_QUEUE'])
        self.mqs = PriorityQueue(self.priority)
        self.status = ScheduleStatus()