Python design pattern series: recursive data structures

I introduce a recursive structure in which you can create and object, and add to it at will.

class ObjectProxy(object):
    def __init__(self, dictionary=None):
        if dictionary:
            for a, b in dictionary.items():
                if isinstance(b, (list, tuple)):
                    setattr(self, a, [ObjectProxy(x)\
                    if isinstance(x, dict) else x for x in b])
                else:
                    setattr(self, a, ObjectProxy(b)\
                    if isinstance(b, dict) else b)

    def __repr__(self):
        return '' % ', '.join(self.__dict__.keys())
    
    def __getattr__(self, attr):
        try:
            return dict.__getattr__(self, attr)
        except:
            if not self.__dict__.has_key(attr):
                self.__dict__[attr] = ObjectProxy()
            return self.__dict__[attr]
        
    def __setattr__(self, attr, value):
        if self.__dict__.has_key(attr) or '__' in attr:
            dict.__setattr__(self, attr, value)
        else:
            self.__dict__[attr] =  value

a = ObjectProxy()
a.b.c.d = 3
a.m.d_ = 2