Why does @foo.setter in Python not work for me?

Question

So, I'm playing with decorators in python 2.6, and I'm having some trouble getting them to work. Here's by class file:

class testDec:

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

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

What I thought this meant is to treat x like a property, but call these function on get and set. So, fire up IDLE and check it:

>>> from testDec import testDec
from testDec import testDec
>>> t = testDec()
t = testDec()
>>> t.x
t.x
called getter
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "testDec.py", line 18, in x
    return self._x
AttributeError: testDec instance has no attribute '_x'
>>> t.x = 5
t.x = 5
>>> t.x
t.x
5

Clearly the first call works as expected, since I call the getter, and there is no default value, and it fails. OK, good, I understand. However, the call to assign t.x = 5 seems to create a new property x, and now the getter doesn't work!

What am I missing?

Answer 1

You need to use new-style classes which you do by deriving your class from object:

class testDec(object):
   ....

Then it should work.

Answer 2

You seem to be using classic old-style classes. In order to properties work correctly you need to use new-style classes instead (inherit from object). Just declare your class as MyClass(object):

class testDec(object):

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

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

---

EDIT: it works. I don't see the reason of the downvotes.

>>> k = testDec()
>>> k.x
called getter
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/devel/class_test.py", line 6, in x
    return self._x
AttributeError: 'testDec' object has no attribute '_x'
>>> k.x = 5
called setter
>>> k.x
called getter
5
>>>