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How to use async and await for asynchronous programming in Python
How to use async and await for asynchronous programming in Python
Sep 21, 2025 am 04:49 AM
Asynchronous functions in Python are defined using async def, allowing non-blocking execution of I/O-bound tasks via await inside coroutines; the asyncio.run() function starts the event loop to run these coroutines, enabling concurrent task execution with asyncio.create_task() and efficient handling of operations like HTTP requests using libraries such as aiohttp.
Using async and await in Python allows you to write asynchronous code that can handle I/O-bound tasks efficiently, such as network requests or file operations, without blocking the main thread. This is done through Python’s asyncio library and coroutines.
Define Asynchronous Functions with async
To create an asynchronous function, use the async def syntax. This turns the function into a coroutine that can be paused and resumed.
async def fetch_data():
print("Start fetching")
await asyncio.sleep(2) # Simulates an I/O operation
print("Done fetching")
return {"data": "example"}
The await keyword is used inside async functions to wait for another coroutine to complete. It only works within async functions and must be used with awaitable objects like coroutines, Tasks, or Futures.
Run Coroutines Using asyncio.run()
To execute an async function, use asyncio.run(), which creates and manages the event loop.
import asyncio <p>async def main(): result = await fetch_data() print(result)</p><p>asyncio.run(main())</p>
asyncio.run() is the recommended way to start an async program from synchronous code. It can only be called once and should not be used inside already running event loops.
Run Multiple Tasks Concurrently
To run multiple coroutines at the same time, use asyncio.create_task() to schedule them, then await their results.
async def task_one():
await asyncio.sleep(1)
return "Task One Done"
<p>async def task_two():
await asyncio.sleep(1)
return "Task Two Done"</p><p>async def main():
task1 = asyncio.create_task(task_one())
task2 = asyncio.create_task(task_two())</p><pre class='brush:php;toolbar:false;'>result1 = await task1
result2 = await task2
print(result1, result2)asyncio.run(main())
This runs both tasks concurrently, reducing total execution time compared to running them sequentially.
Handle Async I/O Operations (e.g., HTTP Requests)
A common use case is making HTTP requests. You can use libraries like aiohttp for async web requests.
import aiohttp import asyncio <p>async def get_page(session, url): async with session.get(url) as response: return await response.text()</p><p>async def main(): async with aiohttp.ClientSession() as session: content = await get_page(session, '<a href="http://ipnx.cn/link/9677548ee4ee2f157590053c5c5f56c4">http://ipnx.cn/link/9677548ee4ee2f157590053c5c5f56c4</a>') print(len(content))</p><p>asyncio.run(main())</p>
Install aiohttp with: pip install aiohttp
This approach allows handling many requests in parallel without blocking each other.
Basically just define async functions, use await on async calls, and run them via asyncio. It's not hard once you get the flow.
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