In Python 2.2.3 there's a problem with accidental 
subclassing from a Python module, e.g.

import MyStuff

class A(MyStuff):
     pass

this gives no error until you try to instantiate the
class:

o = A()

TypeError: 'module' object is not callable

In Python 2.3 the error is generated at module 
startup time:

class A(MyStuff):
     pass
TypeError: function takes at most 2 arguments (3 given)

Since it is rather common that you create modules which
have the same name as their most important class, I
would find it more appropriate to raise a TypeError
with a message "can't subclass a module instance"
in both versions.