AST structures and memory leaks

[Robin Becker]

I want to have an AST container A contain instances of B and would like
the instances to know who contains them, but can't seem to avoid memory
leaks.

The general structure is

class A:
    def __init__(self):
        self.list=[]
    def add(self,b1):
        self.list.append(b)

class B:
    def __init__(self,owner):
        self.owner=owner

a=A()
a.add(B(a))

which is clearly loopy :)

Is there any way to find the 'owner' of an instance?
-- 
Robin Becker