`atexit`

Callbacks registered with atexit run during normal interpreter shutdown, in LIFO order. They do not run on os._exit() or fatal signals.

Source-of-record: Modules/atexitmodule.c, atexit docs.

API

Function	Behaviour
`register(func, args, *kwargs)`	Add a callback; returns `func` (decorator-friendly).
`unregister(func)`	Remove every registration of `func`.
`_run_exitfuncs()`	Force-run all callbacks (testing).
`_clear()`	Drop the registry without running callbacks.

Callbacks run last-in, first-out. Exceptions are caught and printed via sys.excepthook; they do not stop subsequent callbacks.