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I need to use a priority queue in my Python code, and:
Looking around for something efficient, I came upon heapq, but:
heapq, which is implemented in native Python, so it's not fast.heapq, I can either use a (priority, object) as Charlie Martin suggests, or just implement __cmp__ for my object. 
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The Python priority queue is built on the heapq module, which is basically a binary heap. The get command dequeues the highest priority elements from the queue. Priority-object pairs can also be inserted into the queue. This way every task can be associated with a priority.
To implement a priority queue in Python, we have to declare an empty Python list into which elements are inserted using the append() method of list class. The list is then sorted in ascending order. The While loop is used to retrieve the elements using the pop() method.
Project description. heapdict implements the MutableMapping ABC, meaning it works pretty much like a regular Python dict. It's designed to be used as a priority queue, where items are added and consumed as follows: hd = heapdict() hd[obj1] = priority1 hd[obj2] = priority2 # ... ( obj, priority) = hd.popitem()
An ascending order priority queue gives the highest priority to the lower number in that queue. For example, you have six numbers in the priority queue that are 4, 8, 12, 45, 35, 20. Firstly, you will arrange these numbers in ascending order. The new list is as follows: 4, 8, 12, 20.
You can use Queue.PriorityQueue.
Recall that Python isn't strongly typed, so you can save anything you like: just make a tuple of (priority, thing) and you're set.
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When using a priority queue, decrease-key is a must-have operation for many algorithms (Dijkstra's Algorithm, A*, OPTICS), I wonder why Python's built-in priority queue does not support it. None of the other answers supply a solution that supports this functionality.
A priority queue which also supports decrease-key operation is this implementation by Daniel Stutzbach worked perfectly for me with Python 3.5.
from heapdict import heapdict hd = heapdict() hd["two"] = 2 hd["one"] = 1 obj = hd.popitem() print("object:",obj[0]) print("priority:",obj[1]) # object: one # priority: 1 If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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