method decorators and more on decorators

Gabriel Genellina gagsl-py2 at yahoo.com.ar
Wed Jul 30 06:06:08 CEST 2008


En Tue, 29 Jul 2008 08:45:02 -0300, Themis Bourdenas <bourdenas at gmail.com>  
escribi�:

> On Mon, Jul 28, 2008 at 11:12 AM, Gabriel Genellina
> <gagsl-py2 at yahoo.com.ar>wrote:
>
>> En Sun, 27 Jul 2008 15:26:39 -0300, Themistoklis Bourdenas <
>> tbourden at doc.ic.ac.uk> escribió:
>>
>> > On a related note, as the actual instance method of myclass is not foo
>> but
>> > decorate(foo), why are they called method decorators? This does not
>> decorate
>> > methods, they decorate functions and eventually the decorated  
>> functions
>> > become methods. The name method decorator sounds a bit misleading to  
>> me.
>>
>> Where have you found it? I've always seen the expression "function
>> decorator" or just "decorator", not "method decorator".
>
> well a few occurrences of it can be found in PEP 318

In a very strict sense, I'd say that all those references to "method  
decorators" are wrong - because those "def" statements inside a "class"  
statement define functions, not methods. In that sense almost every Python  
programmer is wrong too: in this example

class X:
   @decorator
   def foo(self): pass

most (if not all) people would refer to "foo" as "the foo method in class  
X" - even if foo is really a function, not a method.
So a less restrictive meaning is usually adopted - and we all consider  
"foo" a method, and we're all happy... except in your case, when you just  
hit a point where the distinction is relevant.
Perhaps a more careful wording in the PEP would help in those corner cases.

>> > So returning to my original question is there any way I can get the  
>> class
>> > inside decorate()? I guess there is not, but just asking to make sure.
>>
>> "the class inside decorate"? What do you mean? The type of the x  
>> instance
>> in an x.foo() call? That should be determined inside the wrapped  
>> function
>> -when it is actually called-.
>>
>> Yes, what I was hoping is that it might be possible to get the name of  
>> the
> class the function is eventually is going to be bound to, but I guess  
> that's
> not very likely to be possible. I wanted the name well before the  
> function
> is called, actually even before an instance of the class is created.

No, I think it's not possible - not using a function decorator, because  
when it is applied, the class doesn't exist yet.
You might use a metaclass (or a class decorator, available on 2.6 and  
3.0); iterate over the dictionary of the class about to be created and  
process their functions in any way you like.

> Anyway,
> I 've solved my problem with other means. Just out curiosity though, has
> there been any talk about actual method decorators? I guess you can work
> around them with the introduction of class decorators or even now with
> meta-classes, but you have to wrap methods manually with no syntactic  
> sugar.

Mmm... methods are ephemeral objects, once the call is completed, the  
method usually gets destroyed, so I don't think a true "method decorator"  
would be very useful.
If you really want to customize a method, since they are created by the  
function type's __get__, a crazy idea would be to inherit from the  
function type and return something different in its __get__ - but I've  
never done something like that and don't even know if it's possible at  
all...

-- 
Gabriel Genellina




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