How to make heapq evaluate the heap off of a specific attribute?

According to the example from the documentation, you can use tuples, and it will sort by the first element of the tuple:

>>> h = []>>> heappush(h, (5, 'write code'))>>> heappush(h, (7, 'release product'))>>> heappush(h, (1, 'write spec'))>>> heappush(h, (3, 'create tests'))>>> heappop(h)(1, 'write spec')

So if you don't want to (or can't?) do a __cmp__ method, you can manually extract your sorting key at push time.

Note that if the first elements in a pair of tuples are equal, further elements will be compared. If this is not what you want, you need to ensure that each first element is unique.

heapq sorts objects the same way list.sort does, so just define a method __cmp__() within your class definition, which will compare itself to another instance of the same class:

def __cmp__(self, other):    return cmp(self.intAttribute, other.intAttribute)

Works in Python 2.x.

In 3.x use:

def __lt__(self, other):    return self.intAttribute < other.intAttribute

According to the Official Document, a solution to this is to store entries as tuples (please take a look at Section 8.4.1 and 8.4.2).

For example, your object is something like this in tuple's format(key, value_1, value_2)

When you put the objects (i.e. tuples) into heap, it will take the first attribute in the object (in this case is key) to compare. If a tie happens, the heap will use the next attribute (i.e. value_1) and so on.

For example:

import heapqheap = []heapq.heappush(heap, (0,'one', 1))heapq.heappush(heap, (1,'two', 11))heapq.heappush(heap, (1, 'two', 2))heapq.heappush(heap, (1, 'one', 3))heapq.heappush(heap, (1,'two', 3))heapq.heappush(heap, (1,'one', 4))heapq.heappush(heap, (1,'two', 5))heapq.heappush(heap, (1,'one', 1))show_tree(heap)

Output:

                                      (0, 'one', 1)                                                       (1, 'one', 1)                                (1, 'one', 4)                    (1, 'one', 3)         (1, 'two', 3)         (1, 'two', 2)         (1, 'two', 5)     (1, 'two', 11)

About pretty print a heap in python (updated the link): show_tree()