April 2023
Intermediate to advanced
769 pages
25h 16m
Chinese
Content preview from 流畅的Python（第2版）
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迭代器、生成器和经典协程
｜
497
count += 1
average = total/count
➊
这个函数返回一个生成器，该生成器产出
float
值，通过
.send()
接受
float
值，而且
不返回有用的值。
15
➋
这个无限循环表明，只要客户代码不断发送值，它就会一直产出平均值。
➌
这里的
yield
语句暂停执行协程，把结果发给客户，而且稍后还用于接收调用方后面发
给协程的值，再次开始无限循环迭代。
使用协程的好处是，
total
和
count
声明为局部变量即可，在协程暂停并等待下一次调
用
.send()
期间，无须使用实例属性或闭包保持上下文。正是这一点吸引人们在异步编程
中把回调换成协程，因为在多次激活之间，协程能保持局部状态。
示例
17-38
是使用
averager
协程的
doctest
。
示例
17-38
coroaverager.py
：示例
17-37
中定义的累计平均值协程的
doctest
>>> coro_avg = averager()
➊
>>> next(coro_avg)
➋
0.0
>>> coro_avg.send(10)
➌
10.0
>>> coro_avg.send(30)
20.0
>>> coro_avg.send(5)
15.0
➊
创建协程对象。
➋
开始执行协程。这里产出
average
变量的初始值，即
0.0
。
➌
真正计算累计平均值：多次调用
.send()
方法，产出当前平均值。
在示例
17-38
中
，调用
next(coro_avg)
后，协程向前执行到
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.