Understanding Python Coroutines and Asynchronous HTTP Requests with httpx

During a recent backend refactor, the company switched most logic to asynchronous coroutines using Python's async / await syntax, prompting a deeper exploration of coroutines.

A coroutine is a lightweight, user‑space thread managed by the programmer, offering finer control than OS‑managed threads.

Compared with multithreading, coroutines keep control in user space, reduce context‑switch overhead, use far less stack memory (≈1 KB vs 1 MB), and avoid the need for locks because they run in a single thread.

Coroutines are ideal for I/O‑bound, highly concurrent workloads but unsuitable for CPU‑intensive tasks.

The article then introduces httpx , an async‑capable HTTP client that mirrors the popular requests API while supporting async calls.

Installation is straightforward:

pip install httpx

To illustrate the performance benefit, a synchronous benchmark makes 200 GET requests to http://www.baidu.com using httpx.get , taking about 16.6 seconds.

Code snippet for the synchronous test:

import asyncio import httpx import threading import time def sync_main(url, sign): response = httpx.get(url).status_code print(f'sync_main: {threading.current_thread()}: {sign}: {response}') sync_start = time.time() [sync_main(url='http://www.baidu.com', sign=i) for i in range(200)] sync_end = time.time() print(sync_end - sync_start)

The asynchronous benchmark creates an httpx.AsyncClient and runs 200 concurrent GET requests with await client.get , completing in roughly 4.5 seconds—a 73 % reduction.

Code snippet for the asynchronous test:

import asyncio import httpx import threading import time client = httpx.AsyncClient() async def async_main(url, sign): response = await client.get(url) status_code = response.status_code print(f'async_main: {threading.current_thread()}: {sign}: {status_code}') loop = asyncio.get_event_loop() tasks = [async_main(url='http://www.baidu.com', sign=i) for i in range(200)] async_start = time.time() loop.run_until_complete(asyncio.wait(tasks)) async_end = time.time() loop.close() print(async_end - async_start)

The results show that while the order of async outputs appears random due to coroutine switching, the main thread never switches, confirming the single‑threaded nature of coroutines.

In conclusion, adopting coroutines and async HTTP dramatically speeds up I/O‑bound testing tasks and enhances overall technical proficiency.