Python实现一个优先级队列的方法

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]

>>> 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)
>>> q.pop()
Item('bar')
>>> q.pop()
Item('spam')
>>> q.pop()
Item('foo')
>>> q.pop()
Item('grok')
>>>

>>> a = Item('foo')
>>> b = Item('bar')
>>> a < b
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unorderable types: Item() < Item()
>>>

>>> a = (1, Item('foo'))
>>> b = (5, Item('bar'))
>>> a < b
True
>>> c = (1, Item('grok'))
>>> a < c
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: unorderable types: Item() < Item()
>>>

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