Python异步编程实践

Python异步编程通过事件循环和协程实现高并发I/O操作。

asyncio基础

asyncio是Python内置的异步I/O库。

基本使用

import asyncio

async def main():
    print('Start')
    await asyncio.sleep(1)
    print('End')

asyncio.run(main())
​

创建任务

async def task():
    await asyncio.sleep(1)
    return 'result'

async def main():
    t = asyncio.create_task(task())
    result = await t
    print(result)
​

并发执行

async def fetch(url):
    await asyncio.sleep(1)
    return f'data from {url}'

async def main():
    urls = ['url1', 'url2', 'url3']
    results = await asyncio.gather(*[fetch(u) for u in urls])
    print(results)
​

aiohttp异步HTTP

aiohttp是基于asyncio的异步HTTP框架。

基本请求

import aiohttp

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

并发请求

async def fetch_all(urls):
    async with aiohttp.ClientSession() as session:
        tasks = [fetch(session, url) for url in urls]
        return await asyncio.gather(*tasks)
​

限制并发

async def fetch_limited(urls, limit=10):
    semaphore = asyncio.Semaphore(limit)
    async with aiohttp.ClientSession() as session:
        async def fetch_with_limit(url):
            async with semaphore:
                return await fetch(session, url)
        return await asyncio.gather(*[fetch_with_limit(u) for u in urls])
​

异步编程模式

生产者消费者

async def producer(queue):
    for i in range(5):
        await queue.put(f'item-{i}')

async def consumer(queue):
    while True:
        item = await queue.get()
        if item is None:
            break
        print(item)

async def main():
    queue = asyncio.Queue()
    await asyncio.gather(producer(queue), consumer(queue))
​

超时控制

async def with_timeout():
    try:
        async with asyncio.timeout(3):
            await slow_operation()
    except asyncio.TimeoutError:
        print('timeout')
​

最佳实践

1. 使用asyncio.run()作为入口
2. 避免在协程中使用阻塞操作
3. 控制并发数量避免资源耗尽
4. 使用asyncio.sleep而非time.sleep
5. 合理使用异常处理

Python异步编程适合I/O密集型任务，能显著提升并发性能。