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pythonqueuepriority-queue
Ashok
Ashok

Reputation: 1149

Priority queue with higher priority first in Python

I need a priority queue that gets the item with the highest priority value first. I'm currently using the PriorityQueue Class from the Queue library. However, this function only returns the items with the lowest value first. I tried some ugly solutions like (sys.maxint - priority) as the priority, but was just wondering if a more elegant solution exists.

Upvotes: 25

Views: 23666

Answers (2)

anask
anask

Reputation: 389

You can extend the Priority Queue to keep the logic unchanged:

from Queue import PriorityQueue

class DualPriorityQueue(PriorityQueue):
    def __init__(self, maxPQ=False):
        PriorityQueue.__init__(self)
        self.reverse = -1 if maxPQ else 1

    def put(self, priority, data):
        PriorityQueue.put(self, (self.reverse * priority, data))

    def get(self, *args, **kwargs):
        priority, data = PriorityQueue.get(self, *args, **kwargs)
        return self.reverse * priority, data


minQ = DualPriorityQueue()
maxQ = DualPriorityQueue(maxPQ=True)

minQ.put(10, 'A')
minQ.put(100, 'A')


maxQ.put(10, 'A')
maxQ.put(100,'A')

print "Min DQ: {}".format(minQ.get())
print "Max DQ: {}".format(maxQ.get())

Output:

Min DQ: (10, 'A')
Max DQ: (100, 'A')

Upvotes: 9

Martijn Pieters
Martijn Pieters

Reputation: 1125068

Use a negative priority instead, no need to subtract from sys.maxint.

queue.put((-priority, item))

An item with priority -10 will be returned before items with priority -5, for example.

Upvotes: 47

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