[Python-3000] super(), class decorators, and PEP 3115 (original) (raw)

Phillip J. Eby pje at telecommunity.com
Mon Apr 30 21:35:36 CEST 2007

At 12:17 PM 4/30/2007 -0700, Guido van Rossum wrote:

Hm... Where is the class decorators PEP? I was expecting it.

Assuming class decorators are added, can't you do all of this using a custom metaclass?

The only thing I need for the GF PEP is a way for a method decorator to get a callback after the class is created, so that overloading will work correctly in cases where overloaded methods are defined in a subclass.

In essence, when you define an overloaded method inside a class body, you would like to be able to treat it as if it were defined with "self:class", where class is the enclosing class. In practice, this means that the actual overloading has to wait until the class definition is finished.

In Python 2.x, RuleDispatch implements this by temporary tinkering with metaclass, but if I understand correctly this would not be possible with PEP 3115. I didn't make this connection until I was fleshing out my PEP's explanation of how precedence works when you are overloading instance methods (as opposed to standalone functions).

If PEP 3115 were changed to restore support for metaclass, I could continue to use that approach. Otherwise, some other sort of hook is required.

The class decorator thing isn't an issue for the GF PEP as such; it doesn't use them directly, only via the metaclass hack. I just brought it up because I was looking for the class decorator PEP when I realized that the old way of doing them wouldn't be possible any more.

I'm not sure that your proposal for implementing an improved super has anything over the currently most-favored proposal by Timothy Delaney.

It's merely another use for the hook, that would save on having another special-purpose mechanism strictly for super(); I figured that having other uses for it (besides mine) would be a plus.

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