# example.py
#
# Example of a priority queue
import heapq
class PriorityQueue:
  def __init__(self):
    self._queue = []
    self._index = 0
  def push(self, item, priority):
    heapq.heappush(self._queue, (-priority, self._index, item))
    self._index += 1
  def pop(self):
    return heapq.heappop(self._queue)[-1]
# Example use
class Item:
  def __init__(self, name):
    self.name = name
  def __repr__(self):
    return 'Item({!r})'.format(self.name)
q = PriorityQueue()
q.push(Item('foo'), 1)
q.push(Item('bar'), 5)
q.push(Item('spam'), 4)
q.push(Item('grok'), 1)
print("Should be bar:", q.pop())
print("Should be spam:", q.pop())
print("Should be foo:", q.pop())
print("Should be grok:", q.pop())

Python 3.4.0 (v3.4.0:04f714765c13, Mar 16 2014, 19:24:06) [MSC v.1600 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
>>> ================================ RESTART ================================
>>> 
Should be bar: Item('bar')
Should be spam: Item('spam')
Should be foo: Item('foo')
Should be grok: Item('grok')
>>> 

a=Item('foo')
b=Item('bar')
print('a<b: ',a<b)
>>> 
Traceback (most recent call last):
 File "D:\4autotests\02script\python-cookbook\python-cookbook-master\src\1\5.implementing_a_priority_queue\example.py", line 27, in <module>
  print('a<b: ',a<b)
TypeError: unorderable types: Item() < Item()
>>> 

a=(1,Item('foo'))
b=(5,Item('bar'))
c=(1,Item('gork'))
print('a<b: ',a<b)
print('a<c: ',a<c)
>>> 
a<b: True
Traceback (most recent call last):
 File "D:\4autotests\02script\python-cookbook\python-cookbook-master\src\1\5.implementing_a_priority_queue\example.py", line 29, in <module>
  print('a<c: ',a<c)
TypeError: unorderable types: Item() < Item()
>>> 

a=(1,0,Item('foo'))
b=(5,1,Item('bar'))
c=(1,2,Item('gork'))
print('a<b: ',a<b)
print('a<c: ',a<c)
>>> 
a<b: True
a<c: True
>>>