propertyを使うときはobjectを継承したクラス (new-style class) を使う

new-style classじゃない場合##

class Hoge:
    def __init__(self):
        self._x = 1

    @property
    def x(self):
        print 'property', self._x
        return self._x

    @x.setter
    def x(self, x):
        print 'setter'
        self._x = x

a = Hoge()
print a.x

a.x = 2
print a.x

結果##

property 1
1
2

new-style classの場合##

class Hoge(object):
    def __init__(self):
        self._x = 1

    @property
    def x(self):
        print 'property', self._x
        return self._x

    @x.setter
    def x(self, x):
        print 'setter'
        self._x = x

a = Hoge()
print a.x

a.x = 2
print a.x

結果##

property 1
1
setter
property 2
2

参考##

• http://www.gesource.jp/weblog/?p=643