Why is this Python Borg / Singleton pattern working

Question

i just stumbled around the net and found these interesting code snipped:

http://code.activestate.com/recipes/66531/

class Borg:
    __shared_state = {}
          


        

Answer 1

Because the class's instance's __dict__ is set equal to the __share_state dict. They point to the same object. (Classname.__dict__ holds all of the class attributes)

When you do:

b1.foo = "123"

You're modifying the dict that both b1.__dict__ and Borg.__shared_state refer to.