In Python, heapq.heapify doesn't take cmp or key functions as arguments like sorted does

Question

I\'m using python2.6. Is it available in higher version of python?
Else is there any other way I can maintain priority queues for list of objects of non-trivial classes?

Answer 1

I don't know if this is better but it is like Raymond Hettinger's solution but the priority is determined from the object.

Let this be your object and you want to sort by the the x attribute.

class Item:                                 
    def __init__(self, x):
        self.x = x

Then have a function which applies the pairing

def create_pairs(items):
     return map(lambda item: (item.x, item), items)

Then apply the function to the lists as input into heapq.merge

list(heapq.merge(create_pairs([Item(1), Item(3)]), 
                 create_pairs([Item(2), Item(5)])))

Which gave me the following output

[(1, <__main__.Item instance at 0x2660cb0>),
 (2, <__main__.Item instance at 0x26c2830>),
 (3, <__main__.Item instance at 0x26c27e8>),
 (5, <__main__.Item instance at 0x26c2878>)]