Weak Lists?

[Michael Chermside]

I would like a weak list -- a list in which the values are held with 
weak links. I can write one myself -- particularly if I only support the 
methods I care about (append(), __getitem__(), __iter__(), and sort()), 
but it seems like someone else has probably written (and tested!) this 
already... right?

For those who might be interested, I want this because I am creating a 
tree, with something sort of like this:

    def TreeNode:
        def __init__( self, parent ):
            self.parent = parent
            parent.childNodes.append( self )
            self.childNodes = []

... and I thought it would be nice to let the structure clean up without 
having to invoke the circular reference garbage collector.

-- Michael Chermside