If fact, in the current state it seem that it is impossible to implement real class-properties, for a simple reason: 

descriptor.__set__ is only called when setting the attribute of an instance, but not of a class!!



```python
import math

class TrigConst: 
    const = math.pi
    def __get__(self, obj, objtype=None):
        print("__get__ called")
        return self.const
    
    def __set__(self, obj, value):
        print("__set__ called")
        self.const = value
        

class Trig:
    const = TrigConst()              # Descriptor instance
```

```python
Trig().const             # calls TrigConst.__get__
Trig().const = math.tau  # calls TrigConst.__set__
Trig.const               # calls TrigConst.__get__
Trig.const = math.pi     # overwrites TrigConst attribute with float.
```