# atexit --- Exit handlers

> synopsis: Register and execute cleanup functions. The !atexit module defines functions to register and unregister cleanup functions. Functions thus registered are automatically executed upon normal interpreter termination. !atexit runs these functions in the reverse order in which they were register

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- Updated: `2026-08-16T09:32:14.531948+00:00`
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## Knowledge

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synopsis: Register and execute cleanup functions.

The !atexit module defines functions to register and unregister cleanup functions. Functions thus registered are automatically executed upon normal interpreter termination. !atexit runs these functions in the reverse order in which they were registered; if you register A, B, and C, at interpreter termination time they will be run in the order C, B, A.

Note: The functions registered via this module are not called when the program is killed by a signal not handled by Python, when a Python fatal internal error is detected, or when os._exit is called.

Note: The effect of registering or unregistering functions from within a cleanup function is undefined.

Register func as a function to be executed at termination. Any optional arguments that are to be passed to func must be passed as arguments to register. It is possible to register the same function and arguments more than once.

At normal program termination (for instance, if sys.exit is called or the main module's execution completes), all functions registered are called in last in, first out order. The assumption is that lower level modules will normally be imported before higher level modules and thus must be cleaned up later.

If an exception is raised during execution of the exit handlers, a traceback is printed (unless SystemExit is raised) and the exception information is saved. After all exit handlers have had a chance to run, the last exception to be raised is re-raised.

This function returns func, which makes it possible to use it as a decorator.

Remove func from the list of functions to be run at interpreter shutdown. unregister silently does nothing if func was not previously registered. If func has been registered more than once, every occurrence of that function in the !atexit call stack will be removed. Equality comparisons (==) are used internally during unregistration, so function references do not need to have matching identities.

Module readline Useful example of !atexit to read and write readline history files.

Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.