gistfile1.py

>>> class User(object):
...     username = "bob"
... 
>>> class SuperUser(object):
...     position = "super"    
...     
...     def __init__(self, user):
...         self.user = user
...     
...     def __getattr__(self, attr):
...         return getattr(self.user, attr)
... 
>>> user = User()
>>> superuser = SuperUser(user)
>>> superuser.position
'super'
>>> superuser.username
'bob'
>>> superuser.unknown
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 8, in __getattr__
AttributeError: 'User' object has no attribute 'unknown'