atexit.register in case of errors

Mel Wilson mwilson at the-wire.com
Wed Feb 15 14:33:51 CET 2012


Andrea Crotti wrote:

> I have the following very simplified situation
> 
> from atexit import register
> 
> 
> def goodbye():
>      print("saying goodbye")
> 
> 
> def main():
>      while True:
>          var = raw_input("read something")
> 
> 
> if __name__ == '__main__':
>      register(goodbye)
>      main()
> 
> 
> But in my case the "goodbye" function is deleting the logging file which
> was created
> during the application execution.
> Now the problem is that it *always* executes, even when the applications
> quits for
> some bad errors.
> 
> Is there a way to have an exit hook, which doesn't execute in case of
> errors?
> I've seen the code of atexit and it apparently doesn't know anything
> about the current
> status and why the application is actually quitting, is that correct?

That's sort of the point: to do things that simply *have* to happen, even if 
you've lost control of the program.

The usual way to do what you're asking is

if __name__ == '__main__':
    main()
    goodbye()

and write main so that it returns after it's done all the things it's 
supposed to do.  If you've sprinkled `sys.exit()` all over your code, then 
don't do that.  If you're forced to deal with a library that hides 
`sys.exit()` calls in the functions, then you have my sympathy.  Library 
authors should not do that, and there have been threads on c.l.p explaining 
why they shouldn't.

	Mel.




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