Pourquoi l'utilisation de `property()` avec les méthodes décorées `@classmethod` provoque-t-elle des erreurs en Python ?

class Foo(object):
    _var = 5

    @classmethod
    def getvar(cls):
        return cls._var

    @classmethod
    def setvar(cls, value):
        cls._var = value

    var = property(getvar, setvar)

>>> f = Foo()
>>> f.getvar()
5
>>> f.setvar(4)
>>> f.getvar()
4
>>> f.var
Traceback (most recent call last):
  File <stdin>, line 1, in ?
TypeError: 'classmethod' object is not callable
>>> f.var=5
Traceback (most recent call last):
  File <stdin>, line 1, in ?
TypeError: 'classmethod' object is not callable

class foo(object):
    _var = 5
    
    class __metaclass__(type):  # Python 2 syntax for metaclasses
        pass

    @classmethod
    def getvar(cls):
        return cls._var

    @classmethod
    def setvar(cls, value):
        cls._var = value
    

>>> foo.__metaclass__.var = property(foo.getvar.im_func, foo.setvar.im_func)
>>> foo.var
5
>>> foo.var = 3
>>> foo.var
3