Why does the Python descriptor __set__ not get called

python

Solution

The other two answers allude to using metaclasses to accomplish what you want to do. To help learn about them, here's an example of applying one to the code in your question that makes it do what you want:

class _static_property(object):
    """Descriptor class used for declaring computed properties that
       don't require a class instance.
    """
    def __init__(self, getter, setter):
        self.getter = getter
        self.setter = setter

    def __get__(self, obj, objtype=None):
        print("In the getter function")
        return self.getter(obj)

    def __set__(self, obj, value):
        print("In setter function")
        self.setter(obj, value)

class _MyMetaClass(type):
    def getX(self):
        return self._x

    def setX(self, v):
        self._x = v

    X = _static_property(getX, setX)

class MyTest(object):
    __metaclass__ = _MyMetaClass  # Python 2 syntax
    _x = 42

#class MyTest(object, metaclass=_MyMetaClass):  # Python 3 (only) syntax
#    _x = 42

print(MyTest.__dict__)
print(MyTest.X)
MyTest.X = 12
print(MyTest.X)
print(MyTest.__dict__)

Classes are instances of their metaclass which is normally type `type`. However you can use that as a base class and derive your own specialized meta-subclass -- that in this case is one that has class attributes which are data descriptors (aka properties). Note that the `self` argument in a meta or meta-subclass method is a metaclass instance, which is a class. In code above, it's named `MyTest`.

Problem

Original source