[Python-Dev] Getting rid of unbound methods: patch available

[Guido van Rossum]

> It's about staticmethods. I was writing a class, and its
> pretty-printing method got a function for converting a value to a
> string as an argument. I wanted to supply a default function. I
> thought that it should be in the namespace of the class, since its
> main use lies there. So I made it a staticmethod.
> 
> But - alas! After I declared the function a staticmethod, I couldn't
> make it a default argument for the method, since there's nothing to do
> with staticmethod instances.
> 
> The minor solution for this is to make staticmethod objects callable.
> This would solve my problem. But I suggest a further step: I suggest
> that if this is done, it would be nice if classname.staticmethodname
> would return the classmethod instance, instead of the function itself.
> I know that this things seems to contradict Guido's proposal, since he
> suggests to return the function instead of a strange object, and I
> suggest to return a strange object instead of a function. But this is
> not true; Both are according to the idea that class attributes should
> be, when possible, the same objects that were created when defining
> the class. This is more consistent with the behaviour of modules
> (module attributes are the objects that were created when the code was
> run), and is more consistent with the general convention, that running
> A = B
> causes
> A == B
> to be true. Currently, Class.func = staticmethod(func), and Class.func
> = func, don't behave by this rule. If the suggestions are accepted,
> both will.

Well, given that attribute assignment can be overloaded, you can't
depend on that requirement all the time.

> I just think it's simpler and cleaner that way. Just making
> staticmethods callable would solve my practical problem too.

The use case is fairly uncommon (though not invalid!), and making
staticmethod callable would add more code without much benefits. I
recommend that you work around it by setting the default to None and
substituting the real default in the function.

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)