[Python-3000] PEP: Eliminate __del__

Greg Ewing greg.ewing at canterbury.ac.nz
Sun May 6 01:46:38 CEST 2007

Giovanni Bajo wrote:

> class Holder:
>    def __init__(self):
>       self.resource = ....
>       self.__wr = weakref(self.resource, ....)
> So, are you 
> saying that it's possible that the weakreference refcount goes to zero 
> *before* Holder's refcount?

No, but depending on the order in which the dict contents
gets decrefed when Holder is deallocated, the __wr attribute
may get deallocated before the resource attribute. If that
happens, the callback is never called.

I have run the following code with Python 2.3, 2.4 and 2.5
and it does not print "Cleaning up":

from weakref import ref

class Resource:

def cleanup(x):
     print "Cleaning up"

class Holder:

     def __init__(self):
         self.resource = Resource()
         self.weakref = ref(self.resource, cleanup)

h = Holder()
del h

> Are you saying that the fact that it works for me in real-world code is 
> just out of luck and might randomically break?

If this is really what you're doing, then yes, it will
randomly break. I may have misunderstood exactly what it
is you're doing, however.


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