There is an option in python where you can execute a function when the interpreter terminates.

Consider this below example, save the code in a file and run it.

import atexit


def aa_atexit():
    print('atexit of this aa called')


atexit.register(aa_atexit)
print('started')

$ python3 atexit_example.py

Output:

started
atexit of this aa called

aa_atexit is called just before the interpreter terminates.


As per python documentation:

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.

Consider the below example:

Hence we can register functions to perform cleanup tasks in with atexit. Also, these functions are executed FILO/LIFO (first in last out or last in first out) order.

import atexit


class CC:
    def __init__(self):
        atexit.register(self.gg)

    def gg(self):
        print('atexit of cc called')


class BB:
    def __init__(self):
        atexit.register(self.hh)

    def hh(self):
        print('atexit of bb called')

    def bb(self):
        CC()
        print('bb called')


def aa_atexit():
    print('atexit of this aa called')


atexit.register(aa_atexit)
BB().bb()
print('started')

rana@brahma$ python atexit_experiment.py 
bb called
started
atexit of cc called
atexit of bb called
atexit of this aa called

Just like how we can register the function with atexit, we can unregister the functions as well.

Use of atexit register:

https://mail.python.org/pipermail/python-bugs-list/2009-January/069209.html