__del__ and AttributeError problem

[Gordon McMillan]

Arun Sharma writes:

> class foo:
 /snip snip/

>         def __del__(self):
>                 print "foo dies\n"
>                 bar.something()
 /snip snip/
> Exception exceptions.AttributeError: "'None' object has no attribute
> 'something'" in <method foo.__del__ of foo instance at 80ad0c0>
> ignored bar dies
> 
> 
> Now for the question: why do I get the attribute error ? And what is
> the right way to handle the situation ? I'm using python 1.5.1.

Because of the order in which things happen when Python cleans up. If 
you really have to do something in a __del__ method which might get 
invoked by Python's cleanup, you need to do:

         def __del__(self, something=bar.something):
                 print "foo dies\n"
                 something()

Now bar.something is bound to a default argument which is held deep 
in the bowels of the __del__ method, so it won't go away until the 
containing class gets cleaned out.

Note: this is also a valuable optimization trick. It's significantly 
faster to get the default arg than it is to look up "bar.something".

- Gordon