Understanding async and await in Python with Practical Examples

This article introduces Python's async and await keywords, which enable coroutine programming for asynchronous operations.

async keyword defines a coroutine function. Example:

import asyncio
async def hello_world():
    print("Hello, World!")
# 创建一个事件循环并运行协程
asyncio.run(hello_world())

await keyword suspends the coroutine until another coroutine or async operation completes. Example:

import asyncio
async def sleep_and_print(delay, message):
    await asyncio.sleep(delay)
    print(message)
async def main():
    print(f"Started at {time.strftime('%X')}")
    await sleep_and_print(1, "Hello")
    await sleep_and_print(2, "World")
    print(f"Finished at {time.strftime('%X')}")
# 创建一个事件循环并运行协程
asyncio.run(main())

To run multiple coroutines concurrently, asyncio.gather can combine them. Example:

import asyncio
async def sleep_and_print(delay, message):
    await asyncio.sleep(delay)
    print(message)
async def main():
    print(f"Started at {time.strftime('%X')}")
    task1 = asyncio.create_task(sleep_and_print(1, "Hello"))
    task2 = asyncio.create_task(sleep_and_print(2, "World"))
    await asyncio.gather(task1, task2)
    print(f"Finished at {time.strftime('%X')}")
# 创建一个事件循环并运行协程
asyncio.run(main())

For asynchronous HTTP requests, the aiohttp library can be used. Example:

import asyncio
import aiohttp
async def fetch(session, url):
    async with session.get(url) as response:
        return await response.text()
async def main():
    urls = [
        "https://api.example.com/data1",
        "https://api.example.com/data2",
        "https://api.example.com/data3"
    ]
    async with aiohttp.ClientSession() as session:
        tasks = [fetch(session, url) for url in urls]
        responses = await asyncio.gather(*tasks)
    for response in responses:
        print(response)
# 创建一个事件循环并运行协程
asyncio.run(main())

A more advanced example shows how coroutines can manage resources via a custom ResourceManager class. Example:

import asyncio
class ResourceManager:
    def __init__(self):
        self.resources = {}
    async def acquire(self, resource_id):
        await asyncio.sleep(1)  # 模拟资源获取时间
        print(f"Acquired resource {resource_id}")
        self.resources[resource_id] = True
    async def release(self, resource_id):
        await asyncio.sleep(1)  # 模拟资源释放时间
        print(f"Released resource {resource_id}")
        del self.resources[resource_id]
async def use_resource(manager, resource_id):
    await manager.acquire(resource_id)
    print(f"Using resource {resource_id}")
    await asyncio.sleep(2)  # 模拟使用时间
    await manager.release(resource_id)
    print(f"Released resource {resource_id}")
async def main():
    manager = ResourceManager()
    tasks = [use_resource(manager, i) for i in range(5)]
    await asyncio.gather(*tasks)
# 创建一个事件循环并运行协程
asyncio.run(main())

In summary, async defines coroutine functions, await pauses execution until completion, asyncio.gather enables concurrent coroutines, aiohttp facilitates asynchronous HTTP requests, and coroutines can be used for resource management.