detecting property modification

[Bruno Desthuilliers]

Mangabasi a écrit :
(snip)
>  
> When you say "The Body gets asked for the value of the attribute" that
> means that Body's __dict__ is being asked to provide a value
> corresponding to its 'pos' key, right?

Wrong. That means that attribute lookup rules are invoked, which may *or 
not* end up calling the Body *intance*'s __dict__ __setitem__ method to 
be called. Anyway:

>  Now I may want to ask a more
> specific question here.  How do I modify Body's __dict__ so that I can
> perform a task when __getitem__ method of the __dict__ is called?

This still won't solve your problem. What you want to trace are method 
calls on the objects returned by attribute lookup on instances of Body - 
not calls to instances __dict__ methods. In your example, what you want 
to trace are calls to pos.__getitem__, not calls to b.__dict__.__getitem__.

And if you what you really want is to trace any mutator call to any 
arbitrary object that may become an attribute of b, then I'm afraid 
you're in for a hard time...