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

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You seem to be using classic old-style classes in python 2. In order for properties to work correctly you need to use new-style classes instead (in python 2 you must 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

It works:

>>> 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
>>>

Another detail that might cause problems is that both methods need the same name for the property to work. If you define the setter with a different name like this it won’t work:

@x.setter
def x_setter(self, value):
    ...

And one more thing that is not completely easy to spot at first, is the order: The getter must be defined first. If you define the setter first, you get name 'x' is not defined error.

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