when is a no-op not a no-op?

When is a = a not a no-op?  When a is a class variable accessed through self.a.  May be useful when you want a dynamic initializer for your instances on your class.  For example, a property like time_created.

>>> class A(object):

...    w = 4

...    def __init__(self):

...       self.w = self.w

...

>>> A()

<__main__.A object at 0x00DAE770>

>>> A().__dict__

{'w': 4}

>>> a = A()

>>> a.__dict__

{'w': 4}

>>> a.w = 5

>>> A.w

4

>>> a.w

5