Python中的异步:async 和 await以及操作中的事件循环、回调和异常

import asyncio

import asyncio

async def say_hello():
    print("Hello")
    await asyncio.sleep(1)  # 模拟异步操作
    print("World")

# 异步函数不会立即执行，需要在事件循环中运行

async def main():
    await say_hello()

# 使用 asyncio.run() 启动事件循环并执行异步函数
if __name__ == "__main__":
    asyncio.run(main())

import asyncio
import aiohttp  # 需要安装 aiohttp 库: pip install aiohttp

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

async def main():
    urls = [
        "https://www.example.com",
        "https://www.python.org",
        "https://www.asyncio.org"
    ]
    
    async with aiohttp.ClientSession() as session:
        tasks = [fetch_url(session, url) for url in urls]
        results = await asyncio.gather(*tasks)
        
        for url, content in zip(urls, results):
            print(f"URL: {url}, Content Length: {len(content)}")

if __name__ == "__main__":
    asyncio.run(main())

import asyncio

async def long_running_task():
    await asyncio.sleep(10)
    return "Task completed"

async def main():
    try:
        result = await asyncio.wait_for(long_running_task(), timeout=5)
        print(result)
    except asyncio.TimeoutError:
        print("The task took too long and was cancelled.")

if __name__ == "__main__":
    asyncio.run(main())

import asyncio

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

async def main():
    # 获取事件循环
    loop = asyncio.get_event_loop()
    
    # 创建任务
    task = loop.create_task(say_hello())
    
    # 运行任务
    await task

# 启动事件循环并执行主函数
if __name__ == "__main__":
    asyncio.run(main())

import asyncio

async def slow_operation():
    await asyncio.sleep(2)
    return "Operation Completed"

def callback(future):
    print(future.result())

async def main():
    loop = asyncio.get_event_loop()
    task = loop.create_task(slow_operation())
    task.add_done_callback(callback)
    await task

if __name__ == "__main__":
    asyncio.run(main())

import asyncio

async def error_prone_operation():
    await asyncio.sleep(1)
    raise ValueError("An error occurred")

async def main():
    try:
        await error_prone_operation()
    except ValueError as e:
        print(f"Caught an exception: {e}")

if __name__ == "__main__":
    asyncio.run(main())

import asyncio

async def error_prone_operation():
    await asyncio.sleep(1)
    raise ValueError("An error occurred")

async def main():
    loop = asyncio.get_event_loop()
    task = loop.create_task(error_prone_operation())
    
    try:
        await task
    except ValueError as e:
        print(f"Caught an exception: {e}")
    
    # 或者在任务完成后检查异常
    if task.exception():
        print(f"Task raised an exception: {task.exception()}")

if __name__ == "__main__":
    asyncio.run(main())

import asyncio

async def long_running_task():
    await asyncio.sleep(10)
    return "Task completed"

async def main():
    try:
        result = await asyncio.wait_for(long_running_task(), timeout=5)
        print(result)
    except asyncio.TimeoutError:
        print("The task took too long and was cancelled.")

if __name__ == "__main__":
    asyncio.run(main())