Trouble with assigning (or re-overloading) the assignment operator in Python

Question

I'm having trouble assigning the assignment operator.

I have successfully overloaded __setattr__. But after the object is initialized, I want __setattr__ to do something else, so I try assigning it to be another function, __setattr2__.

Code:

class C(object):

    def __init__(self):
        self.x = 0
        self.__setattr__ = self.__setattr2__

    def __setattr__(self, name, value):
        print "first, setting", name
        object.__setattr__(self, name, value)

    def __setattr2__(self, name, value):
        print "second, setting", name
        object.__setattr__(self, name, value)

c = C()
c.x = 1

What I get:

first, setting x
first, setting __setattr__
first, setting x

What I want/expect:

first, setting x
first, setting __setattr__
second, setting x

Answer 1

From the docs:

Special method lookup for new-style classes

For new-style classes, implicit invocations of special methods are only guaranteed to work correctly if defined on an object’s type, not in the object’s instance dictionary. That behaviour is the reason why the following code raises an exception (unlike the equivalent example with old-style classes):

>>> class C(object):
...     pass
...
>>> c = C()
>>> c.__len__ = lambda: 5
>>> len(c)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: object of type 'C' has no len()

Answer 2

Why not use a flag to indicate that __init__ is still in progress?

class C(object):
    def __init__(self):
        # Use the superclass's __setattr__ because we've overridden our own.
        super(C, self).__setattr__('initialising', True)
        self.x = 0
        # the very last thing we do in __init__ is indicate that it's finished
        super(C, self).__setattr__('initialising', False)

    def __setattr__(self, name, value):
        if self.initialising:
            print "during __init__, setting", name
            # I happen to like super() rather than explicitly naming the superclass
            super(C, self).__setattr__(name, value)
        else:
            print "after __init__, setting", name
            super(C, self).__setattr__(name, value)