[Python-Dev] why different between staticmethod and classmethod on non-callable object?
s7v7nislands at gmail.com
Wed Sep 2 10:24:30 CEST 2009
the three types: function, classmethod, staticmethod are descriptors.
but staticmethod's __get__ return the orignal value, others return
object of instancemethod. (from souce in Objects/funcobject.c)
so the staticmethod just like a wrap that make the wrapped object
'frozen'. like in your example.
is it right? the name and document are mis-understanded.
2009/9/2 P.J. Eby <pje at telecommunity.com>:
> At 08:50 PM 9/1/2009 -0400, Terry Reedy wrote:
>> Greg Ewing wrote:
>>> Benjamin Peterson wrote:
>>>> It depends on whether you're keeping the "callable" object around or
>>>> not. Somebody could add a __call__ method later.
>>> Good point. Removing the check sounds like the
>>> right thing to do, then.
>> Both classmethod & staticmethod are documented as having a *function*
>> (callable, as I interprete that) as their single argument. Seems reasonable
>> to me. Turning the argument into a function after the fact seems like a
>> really esoteric use case.
> The main use case for staticmethod is to prevent __get__ from being called
> on an object retrieved from a class or an instance. It just happens that
> the most common types of objects you'd want to do that on are functions.
> However, if for some reason you intend to make a *descriptor* available as
> an attribute (via a class default), then wrapping it with staticmethod is
> the only easy way to do it.
> For example, if you're writing a class whose instances have an attribute
> that holds a "property" instance, and you want to provide a class-level
> default, the simplest way to do it is to wrap the default property instance
> with staticmethod, so that it's not treated as a property of the
> (Property instances are of course not callable.)
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