====== 第三十章：异步编程 ======

===== 本章目标 =====

完成本章学习后，你将能够：
  * 理解asyncio编程模型
  * 使用async/await
  * 创建和运行协程
  * 处理异步I/O

===== 基础概念 =====

<code python>
import asyncio

async def hello():
    print("Hello")
    await asyncio.sleep(1)
    print("World")

# 运行
asyncio.run(hello())
</code>

===== 创建任务 =====

<code python>
async def task(name, delay):
    print(f"Task {name} started")
    await asyncio.sleep(delay)
    print(f"Task {name} finished")

async def main():
    # 创建任务
    t1 = asyncio.create_task(task("A", 2))
    t2 = asyncio.create_task(task("B", 1))
    
    # 等待完成
    await t1
    await t2

asyncio.run(main())
</code>

===== 并发执行 =====

<code python>
async def main():
    # gather并发执行
    results = await asyncio.gather(
        task("A", 2),
        task("B", 1),
        task("C", 3)
    )
    
    # 等待多个，带超时
    done, pending = await asyncio.wait(
        [task("A", 2), task("B", 1)],
        timeout=1.5
    )

asyncio.run(main())
</code>

===== 异步I/O =====

<code python>
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 = ['https://api.github.com'] * 10
    tasks = [fetch_url(url) for url in urls]
    results = await asyncio.gather(*tasks)

asyncio.run(main())
</code>

===== 本章练习 =====

1. 实现异步HTTP客户端
2. 实现异步爬虫
3. 实现协程调度器

下一章：[[python_course:chapter31|第三十一章：并发模式]]