Python object @property

Question

I'm trying to create a point class which defines a property called "coordinate". However, it's not behaving like I'd expect and I can't figure out why.

class Point:
    def __init__(self, coord=None):
        self.x = coord[0]
        self.y = coord[1]

    @property
    def coordinate(self):
        return (self.x, self.y)

    @coordinate.setter
    def coordinate(self, value):
        self.x = value[0]
        self.y = value[1]

p = Point((0,0))
p.coordinate = (1,2)

>>> p.x
0
>>> p.y
0
>>> p.coordinate
(1, 2)

It seems that p.x and p.y are not getting set for some reason, even though the setter "should" set those values. Anybody know why this is?

Schnabel

What happens if you try to print p.coordinate just after you have instantiated the object, before trying to change it? – Facelifting

This is a gotcha old-style-classes-vs-new-style-classes and you might expect either property() or the IDE would catch it. – Pickerel

Possible duplicate of Property getter/setter have no effect in Python 2 – Cepheus

Answer 1

The property method (and by extension, the @property decorator) requires a new-style class i.e. a class that subclasses object.

For instance,

class Point:

should be

class Point(object):

Also, the setter attribute (along with the others) was added in Python 2.6.

Frenchify

But if I create a property inside a classic class, error raised? – Ankara

Answer 2

It will work if you derive Point from object:

class Point(object):
    # ...

Nahum