[Python-Dev] PEP 447: add type.locallookup (original) (raw)

Ronald Oussoren ronaldoussoren at mac.com
Thu Sep 12 16:25:56 CEST 2013

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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