cpython_sandbox / Doc / library / atexit.rst

:mod:`atexit` --- Exit handlers

The :mod:`atexit` module defines functions to register and unregister cleanup functions. Functions thus registered are automatically executed upon normal interpreter termination. :mod:`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 :func:`os._exit` is called.

:mod:`atexit` Example

The following simple example demonstrates how a module can initialize a counter from a file when it is imported and save the counter's updated value automatically when the program terminates without relying on the application making an explicit call into this module at termination.

    with open("counterfile") as infile:
        _count = int(
except FileNotFoundError:
    _count = 0

def incrcounter(n):
    global _count
    _count = _count + n

def savecounter():
    with open("counterfile", "w") as outfile:
        outfile.write("%d" % _count)

import atexit

Positional and keyword arguments may also be passed to :func:`register` to be passed along to the registered function when it is called:

def goodbye(name, adjective):
    print('Goodbye, %s, it was %s to meet you.' % (name, adjective))

import atexit
atexit.register(goodbye, 'Donny', 'nice')

# or:
atexit.register(goodbye, adjective='nice', name='Donny')

Usage as a :term:`decorator`:

import atexit

def goodbye():
    print("You are now leaving the Python sector.")

This only works with functions that can be called without arguments.