3-Hour Debugging: How `time.sleep` in Async Functions Killed Our asyncio Concurrency

Here’s the situation: we have a data collection service that fetches data from a dozen upstream APIs. The synchronous version took a painful 30 minutes per run. I thought, “This is exactly the kind of problem asyncio was built for!” I spent an afternoon replacing requests with aiohttp , decorating every function with async / await , and ran the code — same 30 minutes. Not a single second faster. I was floored. Eventually, I tracked the culprit to a stray time.sleep(0.5) buried deep inside a nest