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Threads versus processes versus asyncio, what the GIL actually blocks, and choosing per workload.
4 questions in Python.
The Python GIL serializes CPython bytecode execution, but threads still help I/O-bound work; choose processes for pure Python CPU work and asyncio for many concurrent waits.
Python multiprocessing behaves differently across platforms because fork inherits parent memory while spawn starts a fresh interpreter, re-imports the module and requires picklable callables and arguments. It also connects start methods to the point an interviewer is testing.
A timeout requests cancellation; it does not stop code. CancelledError is raised at the task next await point, so a task inside blocking code, shielded, in an executor thread, or swallowing the exception keeps running and commits its side effects late. Fix by re-raising CancelledError, keeping blocking calls off the loop, and using asyncio.timeout with a TaskGroup.
With gather they keep running unsupervised and their failures may surface as an unretrieved-exception warning. A TaskGroup, added in Python 3.11, cancels the siblings, waits for them to finish unwinding, and raises an ExceptionGroup you handle with except*.