Message3204

When accessing an instance attribute defined by a descriptor, any
AttributeError raised by the descriptor itself will be swallowed, and
replaced by the standard AttributeError:

Jython 2.3a0 on java1.6.0_06
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>>> class Desc(object):
...     def __get__(self, instance, type):
...         raise AttributeError("Custom message")     
... 
>>> class Foo(object):
...     desc = Desc()
... 
>>> Foo.desc
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 3, in __get__
AttributeError: Custom message
>>> Foo().desc
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'Foo' object has no attribute 'desc'