How can a Python function be called on script exit reliably?

Question

How do you register a function with all the correct handlers etc to be called when the Python script is exitted (successfully or not)?

I have tried:

@atexit.register
def finalise():
    '''
    Function handles program close
    '''
    print("Tidying up...")
    ...
    print("Closing")

...but this does not get called when the user closes the command prompt window for example (because @atexit.register decorated functions do not get called when the exitcode is non zero)

I am looking for a way of guaranteeing finalise() is called on program exit, regardless of errors.

For context, my Python program is a continually looping service program that aims to run all the time.

Thanks in advance

score 3 · Answer 1 · edited May 23 '17 at 11:46

3

I don't think it can be done in pure Python. From documentation:

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.

I think you may find this useful: How to capture a command prompt window close event in python

edited May 23 '17 at 11:46

Community

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answered Dec 18 '12 at 11:30

Kugel

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score 0 · Answer 2 · answered Dec 18 '12 at 11:28

0

Have you tried to just catch all kinds of exceptions in your main function or code block?

answered Dec 18 '12 at 11:28

djc

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Just tried it, unfortunately it doesn't throw an error when the user closes the command prompt, so it doesn't handle that exit. Thanks for the thought. – James Dec 18 '12 at 11:33

Jakub M. · Answer 3 · 2012-12-18T12:46:15.027

0

This one should work

works both on Ctrl-C and when the assertion fails. Maybe you can use a similar construct and pack it as a decorator, or whatever.

def main():
  print raw_input('> ')
  # do all your stuff here  

if __name__ == '__main__':
  try:
    main()
  finally:
    print 'Bye!'

edited Dec 18 '12 at 12:46

answered Dec 18 '12 at 11:37

Jakub M.

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Okay, not sure I understand how this is to work - could you elaborate a little? Are you saying that `assert` should throw an error when the user closes the command prompt, which is then caught in the `try:...catch:` hence allowing me to handle the exit? – James Dec 18 '12 at 11:48
@James: sorry for confusion, I edited the question. `assert 0` was just an example, that it *will* catch an error and print "Bye". Also, when you press `Ctrl-C`, the `finally` part will be executed. – Jakub M. Dec 18 '12 at 12:47
1

Sorry, I'm afraid that doesn't catch the error of a user closing the command prompt running the Python script. – James Dec 18 '12 at 13:10

score 0 · Answer 4 · edited May 23 '17 at 12:32

0

For context, my Python program is a continually looping service program that aims to run all the time.

This is very hard to get right (see How do you create a daemon in Python?). You should use a library like http://pypi.python.org/pypi/python-daemon/ instead.

edited May 23 '17 at 12:32

Community

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answered Dec 18 '12 at 11:58

Jochen Ritzel

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score -1 · Answer 5 · answered Dec 18 '12 at 11:42

-1

atexit.register(func)

func = lambda x: x

Use http://docs.python.org/2/library/atexit.html

answered Dec 18 '12 at 11:42

Giorgos Komnino

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Yup, not reliable as described above. – James Dec 18 '12 at 11:44
When user closes interpreter probably it is called os.exit() instead of sys.exit() , Correect? – Giorgos Komnino Dec 18 '12 at 11:47
Yup, quite possibly. I need to handle all exiting. – James Dec 18 '12 at 11:49

How can a Python function be called on script exit reliably?

5 Answers5