为什么ClassProp实现不起作用?

基于 a question I previously asked ,我试图想出一个类属性,它既允许设置,也允许获取。所以我写了这个并把它放到一个模块里 util :

class classprop(object):
    def __init__(self, fget, fset=None):
        if isinstance(fget, classmethod):
            self.fget = fget
        else:
            self.fget = classmethod(fget)
        if not fset or isinstance(fset, classmethod):
            self.fset = fset
        else:
            self.fset = classmethod(fset)
    def __get__(self, *a):
        return self.fget.__get__(*a)()
    def __set__(self, cls, value):
        print 'In __set__'
        if not self.fset:
            raise AttributeError, "can't set attribute"
        fset = self.fset.__get__(cls)
        fset(value)

class X(object):
    @classmethod
    def _get_x(cls):
        return 1
    @classmethod
    def _set_x(cls, value):
        print 'You set x to {0}'.format(value)
    x = classprop(fget=_get_x, fset=_set_x)

当“获取”工作时,设置似乎没有被调用:

>>> util.X.x
1
>>> util.X.x = 1
>>> 

我做错什么了?

(我也看到了这种方法的实现有点不同。我特别想知道为什么 这 实现不起作用。)