py2.1->py2.3.3 __getattr__ confusion

[Holger Joukl]

Hi there,
please excuse my rather lengthy post.
With introduction of the new style classes, something
seems to have changed for __getattr__ hooks, even
for classic classes:

getattr.py:
class A: # classic!
    def __getattr__(self, attr):
        print "-->A.__getattr__"
        print "attr=", attr
        print "<--A.__getattr__"
        return self.__dict__[attr]

a = A()
print "a.__dict__:",  a.__dict__
a.foo()
x = a.foo
print "a.foo:", a.foo

$ python2.1 getattr2.py
a.__dict__: {}
A.foo()
a.foo: <method A.foo of A instance at c37d0>

$ python2.3 getattr2.py
a.__dict__: {}
A.foo()
a.foo: -->A.__getattr__
attr= __repr__
<--A.__getattr__
Traceback (most recent call last):
  File "getattr2.py", line 22, in ?
    print "a.foo:", a.foo
  File "getattr2.py", line 6, in __getattr__
    return self.__dict__[attr]
KeyError: '__repr__'

I didn´t find the explanation for this behaviour in the
"what´s new" sections and the docs (and googling).
Probably I missed it - any hints?

Formerly, the instance attribute lookup mechanism was:
1. local __dict__
2. corresponding class definition
3. __getattr__

Now, this seems to work different for the a.foo lookup,
but not for the a.foo() method invocation?!

If I change my class A __getattr__ method in the following way,
I seem to workaround the problem:

class A:
    def __getattr__(self, attr):
        print "-->A.__getattr__"
        print "attr=", attr
        print "<--A.__getattr__"
        return self.__dict__[attr]
        # Use this Try-except-raise AttributeError to get the same
behaviour
        # in python 2.2+ as in python 1.5.2
#        try:
#            return self.__dict__[attr]
#        except KeyError:
#           raise AttributeError

Is this a valid workaround to apply to old __getattr__ hooks?

Thanks for any hints,
 Holger

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