def __init__(self, pqfactory, slot_startprios=None):
        """
        ``pqfactory`` is a factory for creating new PriorityQueues.
        It must be a function which accepts a single optional ``startprios``
        argument, with a list of priorities to create queues for.

        ``slot_startprios`` is a ``{slot: startprios}`` dict.
        """
        self.pqfactory = pqfactory
        self.pqueues = {}  # slot -> priority queue
        for slot, startprios in (slot_startprios or {}).items():
            self.pqueues[slot] = self.pqfactory(startprios)

        ``pqfactory`` is a factory for creating new PriorityQueues.
        It must be a function which accepts a single optional ``startprios``
        argument, with a list of priorities to create queues for.

        ``slot_startprios`` is a ``{slot: startprios}`` dict.
        
stackoverflow/venv/lib/python3.6/site-packages/scrapy/pqueues.py