Question

I have 2 instances x and y of a same class RBnode.
Is there a way to exchange their identities so that all reference to x goes to y and vice versa?

For example,

x = RBnode()
y = RBnode()
x.data = 1
y.data = 2
L = [x,y]

exchange_identity(x,y)
print x.data, y.data, (L[0] is y)

>>> 2 1 True

Actually I’m building an extension of Red-Black tree. Nodes of the tree are implemented as object. When writing the node removal method, I need to exchange two nodes, so that the node to be removed gets “at the bottom” of the tree.

First I tried to just exchange data in the two nodes:

def remove_node(self, y):
    ''' remove node y from tree
    return (y.key,y.value) if successful'''
... ... ...

    # exchange y's data with that of its successor y.next 

    y.key = y.next.key
    y.value = y.next.value

But later an error occurred when remove_node was called and the caller function was holding a reference to a node x, which happens to be y.next. Something like

x = y.next
self.remove_node(y)
x.parent
>>> AttributeError: 'NoneType' object has no attribute 'parent'

I could exchange all corresponding attributes of x and y.
But that takes pretty many lines since the structure of a node is rather complicated.

Answer 1

I must be missing something, because what’s wrong with this?

>>> class RBnode(object):
...   pass
... 
>>> x = RBnode()
>>> y = RBnode()
>>> id(x), id(y)
(20552592, 20552528)
>>> x,y = y,x
>>> id(x), id(y)
(20552528, 20552592)

Or have you meant for reassigning all the names, like some kind of identity theft of an object? While it would be possible working at the C level, I would be pretty surprised if you could do it from within python without breaking things majorly.