Using synchronous HTTP clients like urllib3, requests, or httpx.Client in asynchronous code blocks the
entire event loop. This undermines the primary advantage of asynchronous programming - the ability to perform concurrent operations without blocking
execution.
When an async function makes a synchronous HTTP request:
- The event loop is completely blocked until the HTTP operation completes
- No other coroutines can run during this time, even if they’re ready to execute
- The responsiveness of the application is degraded
- In server applications, this can cause timeouts or failures for other concurrent requests
Instead, async-compatible HTTP clients should be used:
-
httpx.AsyncClient - works with asyncio, Trio, and AnyIO
-
aiohttp.ClientSession - works with asyncio
-
asks - works with Trio and asyncio
Using these libraries allows other tasks to continue executing while waiting for HTTP responses, significantly improving application performance
and responsiveness.
