Python基础教程（九十七）异步IO之协程：Python协程解密，从线程到协程的跃迁之路-优快云博客

一、为什么需要协程？

传统多线程在I/O阻塞时会切换线程，引发上下文切换开销。而协程在单线程内实现并发：当任务遇到I/O等待，主动让出控制权，由事件循环调度其他协程，避免无谓切换。

二、协程核心技术剖析

生成器进化：早期用yield模拟协程，现由async/await原生支持
事件循环(Event Loop)：协程调度中枢，监控I/O事件与任务队列
Future/Task：封装异步操作状态，Task是Future的子类用于管理协程

三、实战示例代码

基础示例：定义与运行

import asyncio

async def hello_coroutine():
    print("Hello")
    await asyncio.sleep(1)  # 模拟I/O操作
    print("Coroutine!")

asyncio.run(hello_coroutine())  # 输出: Hello → (1秒后) Coroutine!

中级：并发执行

async def fetch_data(id, delay):
    print(f"Task {id} started")
    await asyncio.sleep(delay)
    print(f"Task {id} completed")
    return f"Data-{id}"

async def main():
    tasks = [
        fetch_data(1, 2),
        fetch_data(2, 1),
        fetch_data(3, 3)
    ]
    results = await asyncio.gather(*tasks)
    print(f"Results: {results}")  # 按任务顺序返回结果

asyncio.run(main())

输出：

Task 1 started  
Task 2 started  
Task 3 started  
Task 2 completed  # 最先完成  
Task 1 completed  
Task 3 completed  
Results: ['Data-1', 'Data-2', 'Data-3']

高级：网络请求并发

import aiohttp

async def fetch_url(url):
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as response:
            return await response.text()

async def main():
    urls = ["http://httpbin.org/get"] * 5
    tasks = [fetch_url(url) for url in urls]
    pages = await asyncio.gather(*tasks)
    print(f"Fetched {len(pages)} pages concurrently")

asyncio.run(main())