"Phillip J. Eby" wrote: <snip>

...

The AttributeProvider (that my rack have by default) raise an exception in MyItem.__init__ because i and s do not exist (indeed, I want to create them in the instance!)

Could you give the traceback? I think it is more likely your __init__ is failing because you are setting self.id. You should not set self.id directly in your __init__ method, you should call RackMountable's __init__ method like this:

Thanks for the insight. It is a pity that I can't write e-mail from where I work. When I'm back to the office, I will cut and paste the traceback and send it to you tomorrow. I hope it will be useful. You probably noticed that when you are at work, it's time to sleep for me. see you tomorrow :-) we-should-definitely-have-36-hours-a-day-ly yours, Jephte CLAIN minf7@educ.univ-reunion.fr