howto prevent class variable assignment

[Uwe Mayer]

Hi,

when an instance variable of a class is not found, python tries to fall back
to the class variable. 
I want to use that feature to provide default settings for a class which can
be overwritten by assignments to variables with the same name.

This quickly becomes difficult to handle when you get confused wether your
assignment was made to a class variable or an instance variable. I
therefore want to prevent write access to class variables. How do I do
that?

Here some example code:

>>> class A(object):
...   cInt = 5
...   cList = [1,2,3]
...   def __init__(self):
...     self.cInt = 6
... 
>>> a = A()
>>> a.cInt
6
>>> a.__class__.cInt
5

>>> a.cList[2] = 5   #<-- prevent this
>>> a.cList
[1, 2, 5]

>>> a.cInt = 42       #<-- allow this
>>> a.cInt
42
>>> a.__class__.cInt
5

>>>A.cInt = 10       #<-- prevent this

I tried to overwrite __setattr__(self, name, value) method, but this is only
called if I call it on an instance, i.e.

>>> a.cInt = 5

but not when I call it on the class:

>>> A.cInt = 10


Can anyone give me some pointers or suggentions how to handle this?

Thanks
Uwe