[Python-Dev] PEP 447: add type.__locallookup__

[Ronald Oussoren]

On 9 Sep, 2013, at 17:43, Mark Shannon <mark at hotpy.org> wrote:

> I would like time to investigate this further, but at the moment I think it will either make attribute lookup poorly defined or slow.
> 
> Of the top of my head, the problem as a I see it is basically this:
> Currently, type.__getattribute__() is a fixed point in the lookup of attributes.
> The proposal means that a fixed point is not reached until the cls parameter of type.__getattribute__() is either object or type,
> otherwise type.__getattribute__() and type.__locallookup__ must bounce back and forth.
> 
> This will slow down *every* attribute lookup for what is a fairly obscure use case.

I did a benchmark run (see the pep for details) and that seems to indicate that the performance impact is very small, possibly because the patch keeps the attribute lookup cache used by _PyType_Lookup.

Anyway, I'm glad that there is now some real discussion on the proposal. Not unsurprisingly I'd love to have this, or something simular, in 3.4.  I had hoped to repost the PEP a while back with more information on how the API would affect PyObjC (code removal, performance impact), but haven't had time to move forward on that front :-(

Ronald


> 
> Cheers,
> Mark.
> 
> On 09/09/13 16:27, Guido van Rossum wrote:
>> Let's just accept this PEP. It looks like a nice addition to the metaclass machinery and I don't think we'll get much more useful feedback by waiting.
>> 
>> 
>> On Mon, Sep 9, 2013 at 7:30 AM, Ethan Furman <ethan at stoneleaf.us <mailto:ethan at stoneleaf.us>> wrote:
>> 
>>    On 07/30/2013 11:17 PM, Ronald Oussoren wrote:
>> 
>> 
>>        And something I forgot to ask: is anyone willing to be the BDFL-Delegate for
>>        PEP 447?
>> 
>> 
>>    *Bump*.
>> 
>>    It would be nice if this could make into 3.4.
>> 
>>    --
>>    ~Ethan~
>> 
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>> 
>> 
>> --
>> --Guido van Rossum (python.org/~guido <http://python.org/~guido>)
>> 
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