[Python-Dev] @decoration of classes (original) (raw)

Jack Diederich jack at performancedrivers.com
Tue Mar 29 02:55:50 CEST 2005

On Sat, Mar 26, 2005 at 12:36:08PM -0800, Josiah Carlson wrote:

Eric Nieuwland <eric.nieuwland at xs4all.nl> wrote: > > Given the ideas so far, would it possible to: > > def meta(cls): > ... > > @meta > class X(...): > ... It is not implemented in Python 2.4. From what I understand, making it happen in Python 2.5 would not be terribly difficult. The question is about a "compelling use case". Is there a use where this syntax is significantly better, easier, etc., than an equivalent metaclass? Would people use the above syntax if it were available? For compelling, I think the code smell put off by the "no conflict" metaclass generator recipe (which also appeared in Alex Martelli's PyCon talk) is fairly compelling from a duck typing point of view.

would you rather

class K: metaclass = no_conflict(MetaA, MetaB)

or

@decoA @decoB class K: pass

Unless you actually want a class two inherit magic methods from two different types you don't need two metaclasses. You just need the class manipulations that are done in two different metaclasses.

I get around this[1] by defining a function that calls things that manipulate classes, the metaclass's init will make the 'register' function static if it is defined in the dict and then call it with (name, cls). If I called that method 'decorate' instead and spelled it @decorate I'd be a happy camper.

-jackdied

[1] "Register" metatype, define the register method to screw around with your class definition or leave it out to let your parent class do its thing

class Register(type): def init(cls, name, bases, dict): if ('register' in dict): setattr(cls, 'register', staticmethod(dict['register'])) cls.register(name, cls)

I call it Register because largely I just use it to check the dict for special methods and put classes in one or more global buckets. I have cron jobs that operate on the different buckets.

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