[Zope] update existing instances of a class?

[Sascha Ottolski]

Am Freitag, 10. September 2004 01:14 schrieb John Schinnerer:
> Anyone know of more info anywhere on updating existing class
> instances when the class (in a python product) is modified by adding
> some properties?
>
> > Also, you could just add class variables to your object's class
> > which have sensible default.
>
> I don't understand - previous instances will not have the properties
> unless they are updated, correct?

not exactly, I think. If you change the definition of the class to have 
new attributes, every instances of that class will have these 
attributes, too. Of course, they will only have their default values, 
all the same. but at least you can be sure that every instance has the 
attributes.

next step would be to touch every instance to give them their own 
values. this might be a simple as

class MyClass:
    attr = None  # new
    attr2 = ''   # new

    def updateAttr(self, attr, attr2):
        self.attr = attr
        self.attr2 = attr2


Than you might write a PythonScript to find your instances and call the 
updateAttr() method on them.


Hope that helps a bit,

Sascha