property.py

class Property(object):
    def __init__(self):
        self.name = None

    def setup_name(self, obj, cls):
        for k, v in cls.__dict__.iteritems():
            if v is self:
                self.name = k
                obj.__dict__[k] = None
                return

    def __get__(self, obj, cls):
        if obj is None:
            return None

        if self.name is None:
            self.setup_name(obj, obj.__class__)
        return obj.__dict__[self.name]

    def __set__(self, obj, value):
        if self.name is None:
            self.setup_name(obj, obj.__class__)
        obj.__dict__[self.name] = value

if __name__ == "__main__":
    class A(object):
        x = Property()

    obj = A()
    print A.x   # => None
    print obj.x # => None

    obj.x = 10
    print A.x   # => None
    print obj.x # => 10