Question

I want to override access to one variable in a class, but return all others normally. How do I accomplish this with __getattribute__?

I tried the following (which should also illustrate what I’m trying to do) but I get a recursion error:

class D(object):     def __init__(self):         self.test=20         self.test2=21     def __getattribute__(self,name):         if name=='test':             return 0.         else:             return self.__dict__[name]  >>> print D().test 0.0 >>> print D().test2 ... RuntimeError: maximum recursion depth exceeded in cmp 

Answer 1

You get a recursion error because your attempt to access the self.__dict__ attribute inside __getattribute__ invokes your __getattribute__ again. If you use object‘s __getattribute__ instead, it works:

class D(object):     def __init__(self):         self.test=20         self.test2=21     def __getattribute__(self,name):         if name=='test':             return 0.         else:             return object.__getattribute__(self, name) 

This works because object (in this example) is the base class. By calling the base version of __getattribute__ you avoid the recursive hell you were in before.

Ipython output with code in foo.py:

In [1]: from foo import *  In [2]: d = D()  In [3]: d.test Out[3]: 0.0  In [4]: d.test2 Out[4]: 21 

Update:

There’s something in the section titled More attribute access for new-style classes in the current documentation, where they recommend doing exactly this to avoid the infinite recursion.