PEP 318 (was Re: [Python-Dev] Re: Guido's Magic Code was:
Phillip J. Eby
pje at telecommunity.com
Mon Nov 3 20:09:55 EST 2003
At 11:02 AM 11/4/03 +1100, Delaney, Timothy C (Timothy) wrote:
> > From: Alex Martelli [mailto:aleaxit at yahoo.com]
> > BTW, when we do come around to PEP 318, I would suggest the 'as'
> > clause on a class statement as the best way to specify a metaclass.
>I just realised what has been bugging me about the idea of
> def foop() as staticmethod:
>and it applies equally well to
> class Newstyle as type:
>Basically, it completely changes the semantics associated with 'as' in
>Python - which are to give something a different name (technically, to
>rebind the object to a different name).
>OTOH, the first case above means 'create this (function) object, call this
>decorator, and bind the name to the new object'. So instead of taking an
>existing object (with an existing name) and rebinding it to a new name, it
>is creating an object, doing something to it and binding it to a name. A
>definite deviation from the current 'as' semantics, but understandable.
>However, the second case above is doing something completely different. It
>is creating a new object (a class) and binding it to a name. As a side
>effect, it is changing the metaclass of the object. The 'as' in this case
>has nothing whatsoever to do with binding the object name, but a name in
>the object's namespace.
>I suppose you could make the argument that the metaclass has to act as a
>decorator (like in the function def above) and set the __metaclass__
>attribute, but that would mean that existing metaclasses couldn't work. It
>would also mean you were defining the semantics at an implementation level.
>I'm worried that I'm being too picky here, because I *like* the way the
>above reads. I'm just worried about overloading 'as' with too many
>essentially unrelated meanings.
Well, there's always 'is'...
def foop() is staticmethod:
class Newstyle is type:
Interestingly, this usage is rather similar to Eiffel, which IIRC
introduces code suites with 'is', although I think without the modifier.
I'm not all that enthused about the metaclass usage, mainly because there's
already an okay syntax (__metaclass__) for it. I'd rather that class
decorators (if added) were decorators in the same way as function
decorators. Why? Because I think that correct, combinable class
decorators are probably easier for most people to write than correct,
combinable metaclasses, and they are more easily combined than metaclasses are.
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