How can I get the list of registered atexit functions in Python3?

Question

In Python, I can use the atexit module to register function to be executed when Python exits. Is there a way to retrieve the list of registered exit handlers?

Answer 1

here is a pure-python way to access the registered functions (the callable objects), but not the arguments they would be called with. It's a bit of a hack, but for debugging and the like, it will do just fine :

Python 3.5.3 (default, Jul  9 2020, 13:00:10) 
[GCC 6.3.0 20170516] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import atexit
>>> class Capture:
...     def __init__(self):
...         self.captured = []
...     def __eq__(self, other):
...         self.captured.append(other)
...         return False
... 
>>> c = Capture()
>>> atexit.unregister(c)
>>> print(c.captured)
[<function <lambda> at 0x7fc47631d730>, <built-in function write_history_file>]
>>> atexit.unregister(c.captured[0])  # this will work

How it works: as documented, atexit.unregister(c) removes any occurrence of c from the callback list. It does so by comparing each callback in turn with c for equality. This leads to the call c.__eq__(other), with other being the callback (this call is never skipped, as the other way around raises NotImplemented). Capture.__eq__ then copies its argument.