weakref confusion

[Mathias Mamsch]

Hi,

I have some confusion concerning the weakref module.
I am trying to save a weak reference to a bound member function of a class
instance for using it as a callback function. But I always get dead
references, when I try to create a reference to a bound member function. It
seems as if an instance of a class owns no reference to its memberfunctions ,
so the the reference count is always zero. How can I come behind that?


If I do:
----------------
import weakref

class A:
def Test(data): print data

def MyTest (data): print data
AInst = A()

x = weakref.ref (AInst.Test) # x is a dead reference
y = weakref.ref (MyTest) # y is a working reference
f = AInst.Test
z = weakref.ref(f) # z works ...
del f # now z dies ....
----------------

[Jeff Epler]

Re: weakref confusion

On Wed, Feb 25, 2004 at 06:36:59PM +0100, Mathias Mamsch wrote:[color=blue]
> Hi,
>
> I have some confusion concerning the weakref module.[/color]

This is because the class dictionary holds a '<function Test>', but the
expression 'A.Test' returns an '<unbound method A.Test>'. You can
understand why this is the case by looking at what happens in a
subclass:[color=blue][color=green][color=darkred]
>>> class A:[/color][/color][/color]
... def m(): pass[color=blue][color=green][color=darkred]
>>> class B(A): pass
>>> A.m, B.m[/color][/color][/color]
(<unbound method A.m>, <unbound method B.m>)[color=blue][color=green][color=darkred]
>>> A.__dict__['m'][/color][/color][/color]
<function m at 0x813adfc>

just like bound methods on instances, unbound methods are created "on
demand", and are tied to the class that the attribute reference was
performed on.

Jeff