PythonHow-ToBeginner · 3 min read

How to Make Async HTTP Request in Python Easily

To make an async HTTP request in Python, use the aiohttp library with async and await keywords. Create an async function, open a client session, and use await session.get(url) to fetch data without blocking your program.

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Syntax

Here is the basic syntax to make an async HTTP GET request using aiohttp:

async def: Defines an asynchronous function.
aiohttp.ClientSession(): Creates a session to manage connections.
await session.get(url): Sends a GET request asynchronously.
await response.text(): Reads the response body asynchronously.

python

import aiohttp
import asyncio

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

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Example

This example shows how to fetch the content of a webpage asynchronously and print the first 100 characters.

python

import aiohttp
import asyncio

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

async def main():
    url = 'https://www.example.com'
    content = await fetch(url)
    print(content[:100])

asyncio.run(main())

Output

<!doctype html>\n<html>\n<head>\n <title>Example Domain</title>\n <meta charset="utf-8" />\n <meta http-equiv="Content-type" content="text/html; charset=utf-8" />\n <meta name="viewport" content="width=device-width, initial-scale=1" />

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Common Pitfalls

Common mistakes when making async HTTP requests include:

Not using await before async calls, causing coroutines to not run.
Forgetting to use async with for sessions and responses, which can cause resource leaks.
Trying to call async functions without an event loop (e.g., outside asyncio.run()).
Using synchronous libraries like requests inside async code, which blocks the event loop.

python

import aiohttp
import asyncio

# Wrong: missing await
async def wrong_fetch(url):
    async with aiohttp.ClientSession() as session:
        response = await session.get(url)  # Added missing await
        text = await response.text()       # Added missing await
        return text

# Right:
async def right_fetch(url):
    async with aiohttp.ClientSession() as session:
        async with session.get(url) as response:
            return await response.text()

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Quick Reference

Remember these key points when making async HTTP requests in Python:

Use aiohttp library for async HTTP calls.
Always use async with to manage sessions and responses.
Use await to get results from async calls.
Run async code inside an event loop with asyncio.run().

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Key Takeaways

Use aiohttp with async/await to make non-blocking HTTP requests in Python.

Always use async context managers (async with) for sessions and responses to avoid resource leaks.

Never forget to await async calls to actually run them and get results.

Run your async functions inside an event loop using asyncio.run().

Avoid mixing synchronous HTTP libraries like requests in async code.