`async def` vs standard `def` in FastAPI endpoints:

In Simple Words:

• async def: Runs directly on the main AsyncIO event loop thread. Use when calling await on non-blocking async libraries.
• Standard def: FastAPI automatically offloads standard def routes to an internal worker thread pool, preventing blocking code from freezing the event loop!

# Use standard def for legacy synchronous blocking libraries:
import time

@app.get("/sync-task")
def sync_endpoint():
    time.sleep(1) # Safe: FastAPI offloads this to an external thread pool!
    return {"status": "completed"}