Python异步IO库asyncio 协程 学习笔记

asyncio是Python 3.4版本引入的标准库，直接内置了对异步IO的支持。

import asyncio

@asyncio.coroutine
def hello():
    print("Hello world!")
    # 异步调用asyncio.sleep(1):
    r = yield from asyncio.sleep(1)
    print("Hello again!")

# 获取EventLoop:
loop = asyncio.get_event_loop()
# 执行coroutine
loop.run_until_complete(hello())
loop.close()

对yield关键字不清楚的同学看这里:https://blog.csdn.net/mieleizhi0522/article/details/82142856

对yield from关键字不清楚的同学看这里:

https://blog.csdn.net/chenbin520/article/details/78111399    #很棒，推荐

https://blog.csdn.net/soonfly/article/details/78361819

然后，为了简化并更好地标识异步IO，从Python 3.5开始引入了新的语法async和await 

请注意，async和await是针对coroutine的新语法，要使用新的语法，只需要做两步简单的替换：

1. 把@asyncio.coroutine替换为async
2. 把yield from替换为await

再看一个栗子，对比同步IO和异步IO

#同步IO

import time

def hello():
    time.sleep(1)

def run():
    for i in range(5):
        hello()
        print('Hello World:%s' % time.time())  # 任何伟大的代码都是从Hello World 开始的！
if __name__ == '__main__':
    run()

输出是:
Hello World:1527595175.4728756
Hello World:1527595176.473001
Hello World:1527595177.473494
Hello World:1527595178.4739306
Hello World:1527595179.474482





------------------------------------------------------------------------


#异步IO:

import time
import asyncio

# 定义异步函数
async def hello():
    asyncio.sleep(1)
    print('Hello World:%s' % time.time())

def run():
    for i in range(5):
        loop.run_until_complete(hello())

loop = asyncio.get_event_loop()
if __name__ =='__main__':
    run()

输出是:
Hello World:1527595104.8338501
Hello World:1527595104.8338501
Hello World:1527595104.8338501
Hello World:1527595104.8338501
Hello World:1527595104.8338501

再来一个栗子，调用多个协程函数:

import threading
import asyncio
import time

async def hello_A():
    print('A----Hello world! (%s)' % threading.currentThread() , time.time())
    await asyncio.sleep(1)
    print('A----Hello again! (%s)' % threading.currentThread() , time.time())

async def hello_B():
    print('B----Hello world! (%s)' % threading.currentThread() , time.time())
    await asyncio.sleep(1)
    print('B----Hello again! (%s)' % threading.currentThread() , time.time())

loop = asyncio.get_event_loop()
tasks = [hello_A(), hello_B()]
loop.run_until_complete(asyncio.wait(tasks))
loop.close()

Result:
A----Hello world! (<_MainThread(MainThread, started 54064)>) 1568095270.9067237
B----Hello world! (<_MainThread(MainThread, started 54064)>) 1568095270.9067237
A----Hello again! (<_MainThread(MainThread, started 54064)>) 1568095271.9067764
B----Hello again! (<_MainThread(MainThread, started 54064)>) 1568095271.9067764

展示两个错误的调用方式:

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import threading
import asyncio
import time

async def hello_A():
    print('A----Hello world! (%s)' % threading.currentThread() , time.time())
    await asyncio.sleep(1)
    print('A----Hello again! (%s)' % threading.currentThread() , time.time())

async def hello_B():
    print('B----Hello world! (%s)' % threading.currentThread() , time.time())
    await asyncio.sleep(1)
    print('B----Hello again! (%s)' % threading.currentThread() , time.time())

loop = asyncio.get_event_loop()
tasks = [hello_A(), hello_B()]
#loop.run_until_complete(asyncio.wait(tasks))
loop.run_until_complete(hello_A())
loop.run_until_complete(hello_B())
loop.close()

Result:
A----Hello world! (<_MainThread(MainThread, started 47500)>) 1568095328.6755295
A----Hello again! (<_MainThread(MainThread, started 47500)>) 1568095329.6770687
B----Hello world! (<_MainThread(MainThread, started 47500)>) 1568095329.6770687
B----Hello again! (<_MainThread(MainThread, started 47500)>) 1568095330.677155




--------------------------------------------------------------------------------




import threading
import asyncio
import time

async def hello_A():
    while True:
        print('A----Hello world! (%s)' % threading.currentThread() , time.time())
        await asyncio.sleep(1)
        print('A----Hello again! (%s)' % threading.currentThread() , time.time())

async def hello_B():
    while True:
        print('B----Hello world! (%s)' % threading.currentThread() , time.time())
        await asyncio.sleep(1)
        print('B----Hello again! (%s)' % threading.currentThread() , time.time())

loop = asyncio.get_event_loop()
tasks = [hello_A(), hello_B()]
#loop.run_until_complete(asyncio.wait(tasks))
loop.run_until_complete(hello_A())
loop.run_until_complete(hello_B())
loop.close()

Result:
A----Hello world! (<_MainThread(MainThread, started 21096)>) 1568095399.9003077
A----Hello again! (<_MainThread(MainThread, started 21096)>) 1568095400.9008029
A----Hello world! (<_MainThread(MainThread, started 21096)>) 1568095400.9008029
A----Hello again! (<_MainThread(MainThread, started 21096)>) 1568095401.9012694
A----Hello world! (<_MainThread(MainThread, started 21096)>) 1568095401.9012694
A----Hello again! (<_MainThread(MainThread, started 21096)>) 1568095402.9012957
A----Hello world! (<_MainThread(MainThread, started 21096)>) 1568095402.9012957
A----Hello again! (<_MainThread(MainThread, started 21096)>) 1568095403.9016788
A----Hello world! (<_MainThread(MainThread, started 21096)>) 1568095403.9016788

参考资料:

https://www.liaoxuefeng.com/wiki/1016959663602400/1017970488768640

https://blog.csdn.net/m345376054/article/details/78538726