python队列、缺省字典、排序字典
代码语言：javascript复制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]
def __repr__(self):
return '_queue={0},_index={1}'.format(self._queue,self._index)
class Item:
def __init__(self, name):
self.name = name
def __repr__(self):
return 'Item({!r})'.format(self.name)
if __name__=='__main__':
# 优先队列,heapq库
# heappush(heap, x) 将x压入堆中
# heappop(heap) 从堆中弹出最小的元素
# heapify(heap) 让列表具备堆特征
# heapreplace(heap, x) 弹出最小的元素，并将x压入堆中
# nlargest(n, iter) 返回iter中n个最大的元素
# nsmallest(n, iter) 返回iter中n个最小的元素
nums = [8, 1, 2, 3, 7, 5, 6, 4, 0, 9]
# 让列表具备堆特征，否则输出不按照堆的特性
heapq.heapify(nums)
print(heapq.nlargest(3, nums))
# [0, 1, 2]
print(heapq.nsmallest(3, nums))
# [9, 8, 7]
heapq.heappush(nums,11)
# [0, 1, 2, 3, 7, 5, 6, 4, 8, 9, 11]
heapq.heappop(nums)
# [1, 3, 2, 4, 7, 5, 6, 11, 8, 9]
heapq.heapreplace(nums, 12)
# [2, 3, 5, 4, 7, 12, 6, 11, 8, 9]
q = PriorityQueue()
q.push(Item('aaa'), 1)
# _queue=[(-1, 0, Item('aaa'))],_index=1
q.push(Item('bbb'), 5)
# _queue=[(-5, 1, Item('bbb')), (-1, 0, Item('aaa'))],_index=2
q.push(Item('ccc'), 4)
# _queue=[(-5, 1, Item('bbb')), (-1, 0, Item('aaa')), (-4, 2, Item('ccc'))],_index=3
q.push(Item('ddd'), 1)
# _queue=[(-5, 1, Item('bbb')), (-1, 0, Item('aaa')), (-4, 2, Item('ccc')), (-1, 3, Item('ddd'))],_index=4
print(q.pop()) # Item('bbb')
# _queue=[(-4, 2, Item('ccc')), (-1, 0, Item('aaa')), (-1, 3, Item('ddd'))],_index=4
print(q.pop()) # Item('ccc')
# _queue=[(-1, 0, Item('aaa')), (-1, 3, Item('ddd'))],_index=4
print(q.pop()) # Item('aaa')
# _queue=[(-1, 3, Item('ddd'))],_index=4
print(q.pop()) # Item('ddd')
# _queue=[],_index=4
from collections import defaultdict
# defaultdict是Python内建dict类的一个子类，第一个参数为default_factory属性提供初始值，默认为None。
# 它覆盖一个方法并添加一个可写实例变量。
# 它的其他功能与dict相同，但会为一个不存在的键提供默认值，从而避免KeyError异常
bags = ['apple', 'orange', 'cherry', 'apple', 'apple', 'cherry', 'blueberry']
itemcount = defaultdict(int)
for fruit in bags:
itemcount[fruit] = 1
# defaultdict(<class 'int'>, {'apple': 3, 'orange': 1, 'cherry': 2, 'blueberry': 1})
import collections
d1 = {}
d1['a'] = 'A'
d1['c'] = 'C'
d1['b'] = 'B'
# d1={'a': 'A', 'c': 'C', 'b': 'B'}
d2 = {}
d2['a'] = 'A'
d2['b'] = 'B'
d2['c'] = 'C'
# d2={'a': 'A', 'b': 'B', 'c': 'C'}
print(d1==d2) # True
d1 = collections.OrderedDict()
d1['a'] = 'A'
d1['c'] = 'C'
d1['b'] = 'B'
# OrderedDict([('a', 'A'), ('c', 'C'), ('b', 'B')])
d2 = collections.OrderedDict()
d2['a'] = 'A'
d2['b'] = 'B'
d2['c'] = 'C'
# OrderedDict([('a', 'A'), ('b', 'B'), ('c', 'C')])
print(d1==d2) #False
