Like I always did before 3.9, nonetheless: a custom "property" rewrite.

The problem is, "property" does a lot of things, and if one will need everything its in there, it is a lot of code.

I guess it is possible to just subclass property itself, so that we can get an extra .class_getter decorator.

A class setter, obviously, would involve either a custom metaclass or an especialisation of __setattr__.

Let's see if I can come with a reasonably short classproperty.

[after tinkering a bit]

So, it turns out simply inheriting property and adding a decorator for a "class getter" is not easily feasible - "property" is not written with subclassing and expanding its functionality in mind.

Therefore, the "easy" thing, and subset is to write a custom descriptor decorator, which will just convert a single method into a classgetter - and no set, del or inheritance support at all.

On the other hand, the code is short and simple:

class classproperty:
    def __init__(self, func):
        self.fget = func
    def __get__(self, instance, owner):
        return self.fget(owner)

And this simply works as expected:

In [19]: class A:
    ...:     @classproperty
    ...:     def test(cls):
    ...:         return f"property of {cls.__name__}"
    ...: 

In [20]: A.test
Out[20]: 'property of A'

Another way, if one wants to go all the way to have a class attribute setter, it is a matter of writing a plain property on a custom metaclass (which can exist just for holding the desired properties). This approach however will render the properties invisible on the instances - they will work only on the class itself:

In [22]: class MetaA(type):
    ...:     @property
    ...:     def test(cls):
    ...:         return cls._test
    ...:     @test.setter
    ...:     def test(cls, value):
    ...:         cls._test = value.upper()
    ...: 

In [23]: class A(metaclass=MetaA):
    ...:     pass
    ...: 

In [24]: A.test = "hello world!"

In [25]: A.test
Out[25]: 'HELLO WORLD!'

In [26]: A().test
--------------------------------------------------------------
...
AttributeError: 'A' object has no attribute