getting special from type, not instance (was Re: [Python-Dev] copy confusion) (original) (raw)

Armin Rigo arigo at tunes.org
Thu Jan 13 11:16:33 CET 2005

Hi Guido,

On Wed, Jan 12, 2005 at 09:59:13AM -0800, Guido van Rossum wrote:

The descriptor for getattr and other special attributes could claim to be a "data descriptor"

This has the nice effect that x[y] and x.getitem(y) would again be equivalent, which looks good.

On the other hand, I fear that if there is a standard "metamethod" decorator (named after Phillip's one), it will be misused. Reading the documentation will probably leave most programmers with the feeling "it's something magical to put on methods with __ in their names", and it won't be long before someone notices that you can put this decorator everywhere in your classes (because it won't break most programs) and gain a tiny performance improvement.

I guess that a name-based hack in type_new() to turn all *() methods into data descriptors would be even more obscure?

Finally, I wonder if turning all methods whatsoever into data descriptors (ouch! don't hit!) would be justifiable by the feeling that it's often bad style and confusing to override a method in an instance (as opposed to defining a method in an instance when there is none on the class).
(Supporting this claim: Psyco does this simplifying hypothesis for performance reasons and I didn't see yet a bug report for this.)

In all cases, I'm +1 on seeing built-in method objects (PyMethodDescr_Type)
become data descriptors ("classy descriptors?" :-).

Armin

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