[Python-Dev] 'hasattr' is broken by design

[Steve Holden]

On 8/24/2010 9:45 AM, Benjamin Peterson wrote:
> 2010/8/24 Hrvoje Niksic <hrvoje.niksic at avl.com>:
>> On 08/24/2010 02:31 PM, Benjamin Peterson wrote:
>>>
>>> 2010/8/24 Hrvoje Niksic<hrvoje.niksic at avl.com>:
>>>>
>>>>  The __length_hint__ lookup expects either no exception or
>>>> AttributeError,
>>>>  and will propagate others.  I'm not sure if this is a bug.  On the one
>>>> hand,
>>>>  throwing anything except AttributeError from __getattr__ is bad style
>>>> (which
>>>>  is why we fixed the bug by deriving our business exception from
>>>>  AttributeError), but the __length_hint__ check is supposed to be an
>>>> internal
>>>>  optimization completely invisible to the caller of list().
>>>
>>> __length_hint__ is internal and undocumented, so it can do whatever it
>>> wants.
>>
>> Of course, but that's beside the point.  In this case __length_hint__ was
>> neither implemented in the class, nor were we aware of its existence, and
>> the code still broke (as in the example in previous mail).  The point I'm
>> making is that:
>>
>> a) a "business" case of throwing anything other than AttributeError from
>> __getattr__ and friends is almost certainly a bug waiting to happen, and
>>
>> b) making the proposed change is bound to break real, production code.
> 
> I agree with. This is why the change is not making its way into any
> maintenance release.
> 
> 
> 
+1

regards
 Steve
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