Python method reference kills garbage collection?

[Just van Rossum]

Troels Walsted Hansen wrote:

> Consider the following program. What is so special about references to the
> object's own methods that cause the object to never be garbage collected? Is
> this a cyclic reference problem, and if so why doesn't the cycle detector
> (--with-cycle-gc) cure the problem?
> 
> class a:
>     def __init__(self):
>         self.f = self.f1
>     def __del__(self):
>         print "this is never printed"
>     def f1(self):
>         pass
> b=a()
> b=a()

The cycle collector doesn't collect objects of classes with __del__ methods.
(See http://www.python.org/doc/current/lib/module-gc.html for a brief
axplanation.).

Just