All that is needed is a descriptor which calls the decorated functiosn
without any parameters.
This could serve to use classes as namespaces for "live" globals - if one
will do some sort
of reactive programing, it might even find some use.
A descriptor with a for that would be something like:
class staticproperty:
def __init__(self, func, setter=None):
self.func = func
self.setter = setter
def __get__(self, instance, owner):
return self.func
# setter code (won't work statically)
def __set__(self, instance, value):
return self.setter(value)
def setter(self, func):
return type(self)(self.func, func)
I wrote the "setter" code above, but actually it won't work statically -
for the descriptor protocol to call __set__ it must be operating with an
instance of the class. It could still work involving metaclasses - but if
you want the
setter only, the above snippet should work.
Should it be on the stdlib? I don't think so - its usage would be too
specific, and
there are differing interpretations to what it should actually do.
On Sat, 18 Dec 2021 at 14:23, Christopher Barker <[email protected]>
wrote:
> I'm confused about what a staticproperty would even be.
>
> Usually, properties are a way to provide an interface that "looks like" a
> simple attribute, but does some computation under the hood. But that
> computation usually requires instance data to do its thing -- so a static
> one wouldn't be useful.
>
> In fact, in Python, a staticmethod is not very useful at all anyway, all
> it is is a function that lives in the class namespace. Making it a property
> would make it look like a class attribute.
>
> Hmm, I guess one use case would be to make a read only class attribute.
>
> Anyway, the thing is that both staticmethod and property are implimented
> using descriptors, which I think can only be invoked by instance attribute
> lookup. That is, the class attribute IS a descriptor instance.
>
> And Chris A says -- there may be a way to get a similar effect with
> Metaclasses, but we'd have to know what your goal is to advise on how to do
> that.
>
> Note: you can put a descriptor on class, and the __get__ will be called,
> to get part of what I think you want:
>
> In [52]: class Ten:
> ...: def __get__(self, obj, objtype=None):
> ...: return 10
> ...: def __set__(self, obj, value):
> ...: raise AttributeError("attribute can not be set")
> ...:
>
> In [53]: class A:
> ...: y = Ten()
> ...:
>
> # attribute access does call the descriptor's __get__:
>
> In [54]: A.y
> Out[54]: 10
>
> But setting the attribute replaces the descriptor, rather than raising an
> exception:
>
> In [55]: A.y = 12
>
> In [56]: A.y
> Out[56]: 12
>
> Honestly, I don't quite "get" how all this works, but the usual thing is
> for Descriptors to be invoked on instance attribute access.
>
> -CHB
>
>
> On Sat, Dec 18, 2021 at 8:30 AM <[email protected]> wrote:
>
>> In the following situations:
>>
>>
>> class Data(object):
>> @staticmethod
>> @property
>> def imagesTotal():
>> return 10
>>
>> print(Data.imagesTotal)
>>
>>
>> The "print(Data.imagesTotal)" can't print "10", it print "<property
>> object at 0x...>".
>>
>> It might be a good idea to use "@staticproperty" to solve this problem.
>> "@staticproperty" is a decorators, it mix the @staticmethod and @property.
>> Then the static property has getter and setter.
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>>
>
>
> --
> Christopher Barker, PhD (Chris)
>
> Python Language Consulting
> - Teaching
> - Scientific Software Development
> - Desktop GUI and Web Development
> - wxPython, numpy, scipy, Cython
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