Python atexit.register not being called after termination

Question

I am working on a program that needs to call a function right before exiting, and was successfully using atexit.register(myFunction) to do so, until it stopped working. Even when I try running just a simple script, the registered function is not being called...

Here is the simple code:

import atexit def all_done(): print ('all_done()') print ('Registering') atexit.register(all_done) print ('Registered')

And the output is:

Registering Registered

When it should be:

Registering Registered all_done()

What could be the problem? Like I said, it was working for a while, then suddenly stopped.

I'm not able to reproduce your problem. I'm getting your expected output. — Fred Larson
– Fred Larson, Commented Mar 24, 2020 at 21:42
Like I said, it was working at one point. I get the sense that something must have messed up the module somehow, because I don't think anything is wrong with the code. — Patricia
– Patricia, Commented Mar 24, 2020 at 21:58
There isn't enough to go on, so a bit of a wild guess... the interpreter actually never terminates (i.e. you're using IDE that keeps the session alive)? The other options being, it gets terminated by a signal which is (can)not be handled and interpreter terminates without calling registered function? — Ondrej K.
– Ondrej K., Commented Mar 24, 2020 at 22:17

JEREDEK · Accepted Answer · 2023-08-22 14:47:46Z

Welcome, 2 year old post. In case you're having the same problem: keep in mind that, quote, "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."

That means things like a system shutdown or os._exit() won't call the atexit function, but things like a keyboard interrupt or sys.exit() will do no problem.

example:

import atexit def all_done(): print ('all_done()') print ('Registering') atexit.register(all_done) print ('Registered') os._exit()

will output

Registering Registered

But, this code here:

import atexit def all_done(): print ('all_done()') print ('Registering') atexit.register(all_done) print ('Registered') sys.exit()

will output

Registering Registered all_done()

Hope i was of help!

source: https://docs.python.org/3/library/atexit.html

Patricia · Accepted Answer · 2020-03-25 11:23:18Z

I ended up not using atexit, instead just

try: ... finally: ...

which is now working. Still don't know why atexit doesn't work, though...

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