佇列deque（python3）

from collections import deque

deque的方法可以用help(deque)檢視

1，建立無界限佇列

2，建立定長佇列

3，利用佇列儲存匹配行

注：編寫搜尋某項記錄的程式碼時，通常會用到含有yield關鍵字的生成器函式。yield使用淺析可以參考點選開啟連結      

from collections import deque


def my_search(lines, pattern):
    # 獲取文字中含有某個欄位的行
    for line in lines:
        if pattern in line:
            yield line


if __name__ == '__main__':
    try:
        with open('somefile.txt', 'r') as fObj:
            result = deque(maxlen=3)
            for line in my_search(fObj, 'python'):
                result.append(line)
            print(result)
    except:
        pass
 

輸出：

deque(['to python\n', 'you python\n', 'sdfsdfsdf python'], maxlen=3)

4，heapq模組的使用

import heapq

通過help(heapq)可看到heapq的方法，使用方法可參考點選開啟連結

4.1,找到最大或最小的N個元素，merge兩個列表

>>> list1 = [2,3,3,8,9]
>>> print(heapq.nlargest(2,list1))
[9, 8]
>>> print(heapq.nsmallest(2,list1))
[2, 3]
>>> for i in heapq.merge(list1, [5,4,8]):
	print(i, end=',')

	
2,3,3,5,4,8,8,9,
>>> 
 

import heapq


class PriorityQueue:
    #優先順序佇列
    def __init__(self):
        self._queue = []
        self._index = 0

    def push(self, item, priority):
        # heapq的堆是小頂堆，priority取負是為了heappop得到的總是最小的元素
        heapq.heappush(self._queue, (-priority, self._index, item))
        self._index += 1

    def pop(self):
        # [-1]返回item物件
        return heapq.heappop(self._queue)[-1]

    def print(self):
        # 列印這個佇列
        for i in self._queue:
            print(i, end='\n')
        
            
class Item:
    def __init__(self, name):
        self.name = name

    def __repr__(self):
        return 'Item({!r})'.format(self.name)
    

q = PriorityQueue()
q.push(Item('foo1'), 1)
q.push(Item('foo4'), 4)
q.push(Item('foo5'), 5)
q.push(Item('foo2'), 2)
q.push(Item('foo3'), 3)
q.push(Item('foo11'), 1)
q.push(Item('foo55'), 5)
q.print()
print('-----pop----')
print(q.pop())
print(q.pop())
print(q.pop())
print(q.pop())
print(q.pop())
print(q.pop())
print(q.pop())
 

輸出：

(-5, 2, Item('foo5'))
(-3, 4, Item('foo3'))
(-5, 6, Item('foo55'))
(-1, 0, Item('foo1'))
(-2, 3, Item('foo2'))
(-1, 5, Item('foo11'))
(-4, 1, Item('foo4'))
-----pop----
Item('foo5')
Item('foo55')
Item('foo4')
Item('foo3')
Item('foo2')
Item('foo1')
Item('foo11')