Dynamically change __del__

Peter Otten __peter__ at web.de
Fri Apr 30 21:47:40 CEST 2010


Nikolaus Rath wrote:

> Apparently Python calls the class attribute __del__ rather than the
> instance's __del__ attribute. Is that a bug or a feature? Is there any
> way to implement the desired functionality without introducing an
> additional destroy_has_been_called attribute?

For newstyle classes __special__() methods are always looked up in the 
class, never in the instance.

Your best bet is probably to manage the lifetime of the instance explicitly 
with try...finally or a context manager:

>>> import contextlib
>>> class T(object):
...     def close(self):
...             print "Cleaning up."
...
>>> with contextlib.closing(T()) as t:
...     print t
...
<__main__.T object at 0x7fc50c1e61d0>
Cleaning up.

Alternatively you can try and cook up something with weakref.ref and a 
callback.

Peter



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