python协程

润森

发布于 2019-11-10 15:39:22

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发布于 2019-11-10 15:39:22

文章被收录于专栏：毛利学Python

学习一时爽，一直学习一直爽

Hello，大家好，我是もうり，一个从无到有的技术+语言小白。

协程是实现并发编程的一种方式。

https://docs.python.org/zh-cn/3/library/asyncio.html

一说并发，你肯定想到了多线程 / 多进程模型，没错，多线程 / 多进程，正是解决并发问题的经典模型之一

协程：是单线程下的并发，又称微线程。英文名 Coroutine。

协程比线程的单位更小——协程

注意协程这个概念完全是程序员自己想出来的东西，它对于操作系统来说根本不存在。操作系统只知道进程和线程。

从

import timedef print_num(num):    print("Maoli is printing " + str(num) + " nows" )    time.sleep(1)    print("Maoli prints" + str(num) + " OK")def main(nums):    for num in nums:        print_num(num)%time main([i for i in range(1,6)])Maoli is printing 1 nowsMaoli prints1 OKMaoli is printing 2 nowsMaoli prints2 OKMaoli is printing 3 nowsMaoli prints3 OKMaoli is printing 4 nowsMaoli prints4 OKMaoli is printing 5 nowsMaoli prints5 OKWall time: 5 s

将上面代码改为协程版

注意 py 版本 3.7 以上

import asyncioasync def print_num(num):    print("Maoli is printing " + str(num) + " nows" )    await asyncio.sleep(1)    print("Maoli prints" + str(num) + " OK")async def main(nums):    for num in nums:        await print_num(num)%time asyncio.run(main([i for i in range(1,6)]))Maoli is printing 1 nowsMaoli prints1 OKMaoli is printing 2 nowsMaoli prints2 OKMaoli is printing 3 nowsMaoli prints3 OKMaoli is printing 4 nowsMaoli prints4 OKMaoli is printing 5 nowsMaoli prints5 OKWall time: 5.01 s

asyncio.run() 函数用来运行最高层级的入口点 "main()" 函数

await 是同步调用等待一个协程。以下代码段会在等待 1 秒后打印 num，

可等待对象

如果一个对象可以在 await 语句中使用，那么它就是可等待对象

协程中的还一个重要概念，任务（Task）

如果写一个数字是一个任务，那么毛利我要完成 5 个任务

毛利我写个 1-5 都这么慢，不行，我要加速写

asyncio.create_task() 函数用来并发运行作为 asyncio 任务的多个协程。

import asyncioasync def print_num(num):    print("Maoli is printing " + str(num) + " nows" )    await asyncio.sleep(1)    print("Maoli prints" + str(num) + " OK")async def main(nums):    tasks = [asyncio.create_task(print_num(num)) for num in nums]    for task in tasks:        await task%time asyncio.run(main([i for i in range(1,6)]))Maoli is printing 1 nowsMaoli is printing 2 nowsMaoli is printing 3 nowsMaoli is printing 4 nowsMaoli is printing 5 nowsMaoli prints1 OKMaoli prints3 OKMaoli prints5 OKMaoli prints2 OKMaoli prints4 OKWall time: 1.01 s

还可以写成 await asyncio.gather(*tasks)这种方法

import asyncioasync def print_num(num):    print("Maoli is printing " + str(num) + " nows" )    await asyncio.sleep(1)    print("Maoli prints" + str(num) + " OK")async def main(nums):    tasks = [asyncio.create_task(print_num(num)) for num in nums]    await asyncio.gather(*tasks)%time asyncio.run(main([i for i in range(1,6)]))

*tasks 解包列表，将列表变成了函数的参数；与之对应的是， ** dict 将字典变成了函数的参数。

asyncio 队列

asyncio 队列被设计成与 queue 模块类似。

import asyncioimport randomasync def consumer(queue, id):    while True:        val = await queue.get()        print('{} get a val: {}'.format(id, val))        await asyncio.sleep(1)async def producer(queue, id):    for i in range(5):        val = random.randint(1, 10)        await queue.put(val)        print('{} put a val: {}'.format(id, val))        await asyncio.sleep(1)async def main():    # 创建队列    queue = asyncio.Queue()    # 消费者1号    consumer_1 = asyncio.create_task(consumer(queue, 'consumer_1'))    # 消费者2号    consumer_2 = asyncio.create_task(consumer(queue, 'consumer_2'))    # 生产者1号    producer_1 = asyncio.create_task(producer(queue, 'producer_1'))    # 生产者2号    producer_2 = asyncio.create_task(producer(queue, 'producer_2'))    # stop 10秒    await asyncio.sleep(10)    consumer_1.cancel()    consumer_2.cancel()    await asyncio.gather(consumer_1, consumer_2, producer_1, producer_2, return_exceptions=True)%time asyncio.run(main())

协程的写法简洁清晰，把 async / await 语法和 create_task 结合来用。

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原始发表：2019-11-09，如有侵权请联系 cloudcommunity@tencent.com 删除

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