Class property (was: Class methods)

Bengt Richter bokr at oz.net
Sat Oct 15 04:10:50 CEST 2005


On Thu, 06 Oct 2005 11:05:10 +0200, Laszlo Zsolt Nagy <gandalf at designaproduct.biz> wrote:

>Hughes, Chad O wrote:
>
>> Is there any way to create a class method?  I can create a class 
>> variable like this:
>>
>Hmm, seeing this post, I have decided to implement a 'classproperty' 
>descriptor.
>But I could not. This is what I imagined:
>
>class A(object):
>    _x = 0
>    @classmethod
>    def get_x(cls):
>        print "Getting x..."
>        return cls._x
>    @classmethod
>    def set_x(cls,value):
>        print "Setting x..."
>        cls._x = value
>    x = classproperty(get_x,set_x)
>
>Usage example:
>
> >>>print A.x
>Getting x
>0
> >>>A.x = 8
>Setting x
> >>>print A.x
>Getting x
>8
>
>I was trying for a while, but I could not implement a 'classproperty' 
>function. Is it possible at all?
>Thanks,
>
>   Les
>
Using Peter's advice (not tested beyond what you see):

 >>> class A(object):
 ...     _x = 0
 ...     class __metaclass__(type):
 ...         def get_x(cls):
 ...             print "Getting x..."
 ...             return cls._x
 ...         def set_x(cls,value):
 ...             print "Setting x..."
 ...             cls._x = value
 ...         x = property(get_x, set_x)
 ...
 >>> A.x
 Getting x...
 0
 >>> A.x = 8
 Setting x...
 >>> A.x
 Getting x...
 8
 >>> vars(A).items()
 [('__module__', '__main__'), ('__metaclass__', <class '__main__.__metaclass__'>), ('_x', 8), ('_
 _dict__', <attribute '__dict__' of 'A' objects>), ('__weakref__', <attribute '__weakref__' of 'A
 ' objects>), ('__doc__', None)]
 >>> A._x
 8
 >>> vars(A).keys()
 ['__module__', '__metaclass__', '_x', '__dict__', '__weakref__', '__doc__']

Regards,
Bengt Richter



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