這個文章理好了脈落。

http://python.jobbole.com/86069/

我練 習了一番，感受好了很多。。。

Python由于眾所周知的GIL的原因，導致其線程無法發揮多核的并行計算能力（當然，后來有了multiprocessing，可以實現多進程并行），顯得比較雞肋。既然在GIL之下，同一時刻只能有一個線程在運行，那么對于CPU密集的程序來說，線程之間的切換開銷就成了拖累，而以I/O為瓶頸的程序正是協程所擅長的：

多任務并發（非并行），每個任務在合適的時候掛起（發起I/O）和恢復(I/O結束)

弄清楚了asyncio.coroutine和yield from之后，在Python3.5中引入的async和await就不難理解了：可以將他們理解成asyncio.coroutine/yield from的完美替身。當然，從Python設計的角度來說，async/await讓協程表面上獨立于生成器而存在，將細節都隱藏于asyncio模塊之下，語法更清晰明了。

#!/usr/bin/env python # -*- coding: utf-8 -*-import asyncio import time import random''' def old_fib(n):res = [0] * nindex = 0a = 0b = 1while index < n:res[index] = ba, b = b, a + bindex += 1return resprint("-"*10 + "test old fib " + "-"*10) for fib_res in old_fib(20):print(fib_res)def fib(n):index = 0a = 0b = 1while index < n:yield ba, b = b, a + bindex += 1print("-"*10 + "test yield fib " + "-"*10) for fib_res in fib(20):print(fib_res)def stupid_fib(n):index = 0a = 0b = 1while index < n:sleep_cnt = yield bprint("let me think {0} secs".format(sleep_cnt))time.sleep(sleep_cnt)a, b = b, a + bindex += 1 print("-"*10 + "test yield send " + "-"*10) N = 20 sfib = stupid_fib(N) fib_res = next(sfib) while True:print(fib_res)try:fib_res = sfib.send(random.uniform(0, 0.5))except StopIteration:breakdef copy_fib(n):print("I am copy from fib")yield from fib(n)print("copy end") print("-"*10 + "test yield from " + "-"*10) for fib_res in copy_fib(20):print(fib_res)def copy_stupid_fib(n):print("I am copy from stupid fib")yield from stupid_fib(n)print("Copy end")print("-"*10 + "test yield from and send" + "-"*10) N = 20 csfib = copy_stupid_fib(N) fib_res = next(csfib) while True:print(fib_res)try:fib_res = csfib.send(random.uniform(0, 0.5))except StopIteration:break@asyncio.coroutine def smart_fib(n):index = 0a = 0b = 1while index < n:sleep_secs = random.uniform(0, 0.2)yield from asyncio.sleep(sleep_secs)print("Smart one think {} secs to get {}".format(sleep_secs, b))a, b = b, a + bindex += 1@asyncio.coroutine def stupid_fib(n):index = 0a = 0b = 1while index < n:sleep_secs = random.uniform(0, 0.4)yield from asyncio.sleep(sleep_secs)print("Stupid one think {} secs to get {}".format(sleep_secs, b))a, b = b, a + bindex += 1loop = asyncio.get_event_loop() tasks = [asyncio.async(smart_fib(10)),asyncio.async(stupid_fib(10)),] loop.run_until_complete(async.wait(tasks)) print("All fib finished.") loop.close()'''async def smart_fib(n):index = 0a = 0b = 1while index < n:sleep_secs = random.uniform(0, 0.2)await asyncio.sleep(sleep_secs)print("Smart one think {} secs to get {}".format(sleep_secs, b))a, b = b, a + bindex += 1async def stupid_fib(n):index = 0a = 0b = 1while index < n:sleep_secs = random.uniform(0, 0.4)await asyncio.sleep(sleep_secs)print("Stupid one think {} secs to get {}".format(sleep_secs, b))a, b = b, a + bindex += 1loop = asyncio.get_event_loop() tasks = [asyncio.async(smart_fib(10)),asyncio.async(stupid_fib(10)),] loop.run_until_complete(asyncio.wait(tasks)) print("All fib finished.") loop.close()

Python中的協程經歷了很長的一段發展歷程。其大概經歷了如下三個階段：

最初的生成器變形yield/send

引入@asyncio.coroutine和yield from

在最近的Python3.5版本中引入async/await關鍵字

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