Asyncio
This section is less about the syntax of `async def` and more about how to run asynchronous systems safely. Event loops, tasks, cancellation, timeouts, backpressure, and debug mode all belong to one operating model.
Quick takeaway: good asyncio code is not just "high concurrency." It is code that handles cancellation and cleanup correctly, limits input pressure, and removes hidden blocking I/O.
The Questions This Part Builds
When does work become a task?
A coroutine object and a scheduled task are not the same thing. You need to know what is actually on the event loop.
Why is cancellation an exception?
Cancellation is modeled as exception propagation, so cleanup and re-raising matter a lot.
Why is backpressure mandatory?
Unlimited queues and unlimited fan-out make async systems fail through overload rather than through slow code.
How do you debug timing bugs?
Async bugs need timeout guards, debug mode, and task-leak checks more than they need clever print statements.
Recommended Order
Practical Rules
- If you create a task, ownership of waiting, cancellation, and error collection must be clear.
- Do not call blocking functions directly in the event loop.
- Always limit queue size and concurrency.
- Treat timeout and cleanup paths as first-class behavior.