def __set__(self, obj, value):
previousValue = getattr(obj, self.name)<EOL>super(observable_property, self).__set__(obj, value)<EOL>obj.diffuse(self.name, previousValue, value)<EOL>
Override the computed value of the property to
diffuse the change to observer.

:param obj: The instance that owns the property.
:param value: The new value for the property.