yield, async

yield實現斐波那契序列：

import sys, time

def fib():
    a,b,c = 0,1,0
    while True:
        yield c
        a,b = b, c
        c = a + b
        
if __name__ == '__main__':
    fib_iter = fib()
    for i in range(int(sys.argv[1])):
        print(fib_iter.__next__())

Send:

send函數用來向fib_iter發送數據，這樣數據就可以雙向流動。我們嘗試使用send來模擬一個比較慢的生成器，我們讓它一秒鐘生成一個數：

import sys, time

def fib():
    a,b,c = 0,1,0
    while True:
        sleep_sec = yield c
        time.sleep(sleep_sec)
        a,b = b, c
        c = a + b

def fib1():
    index = 1
    a = 0
    b = 1
    while index:
        yield b
        a, b = b, a + b
        index += 1
        
if __name__ == '__main__':
    fib_iter = fib()
    print(fib_iter.__next__())    #先執行一下，讓它停留在yield
    for i in range(int(sys.argv[1])):
        result = fib_iter.send(1)   #
        print(result)

yield from 是什麼？

  在上面的yield中，我們通過for迴圈使用__next__()方法來獲取下一個值，也就是說想要獲取下一個值就要重新yield一下；yield from 它可以簡化這個過程，看看實例：

import sys, time

def fib(n):
    a,b,c = 0,1,0
    while c < n:
        yield c
        a,b = b, c
        c = a + b

def gener(n):
    yield from fib(n)
        
if __name__ == '__main__':
    print(list(gener(5000)))

執行結果：

D:\>python fib.py
[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4
181]

yield from ， send傳遞信息：

import sys, time

def fib(n):
    a,b,c = 0,1,0
    while c < n:       
        sleep_sec = yield c
        time.sleep(sleep_sec)
        a,b = b, c
        c = a + b

def gener(n):
    yield from fib(n)
        
if __name__ == '__main__':
    gen = gener(10)
    print(gen.send(None))
    print(gen.send(1))
    print(gen.send(1))

執行結果：

D:\>python fib.py
0
1
1

asyncio 和 yield from:

asyncio是一個基於事件迴圈的實現非同步的I/O模塊。通過yield from, 我們可以將協程asynico.sleep的控制權交給事件迴圈，然後掛起當前協程；之後，由事件迴圈決定何時喚醒asyncio.sleep，然後接著執行後面的代碼; 實例中我們用sleep來模擬阻塞：

import sys, time, asyncio

def fib(n):
    a,b,c = 0,1,0
    while c < n:  
        yield from asyncio.sleep(2)
        print('-->', c)
        a,b = b, c
        c = a + b

def stupid_fib(n):
    a,b,c = 0,1,0
    while c < n:
        yield from asyncio.sleep(2)
        print('==>', c)
        a,b = b,c
        c = a + b
        
if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    tasks = [asyncio.async(fib(10)), asyncio.async(stupid_fib(10))]
    loop.run_until_complete(asyncio.wait(tasks))
    print('all task finished')
    loop.close()

執行結果：

D:\>python fib.py
--> 0
==> 0
--> 1
==> 1
--> 1
==> 1
--> 2
==> 2
--> 3
==> 3