Mangabasi a écrit : > On Dec 21, 4:46 pm, Bruno Desthuilliers > <[EMAIL PROTECTED]> wrote: > >>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... > > > Now I am curious about these "attribute lookup rules". > My understanding was: > > When an attribute name is accessed in an instance > > First __getattribute__(self, name) is called.
Which is itself resolved first (methods being attributes) !-) __getattribute__ can itself be overloaded, so the only thing you can bet is that the first __getattribute__ method found in the mro will be called. All the rest is the *default* lookup rule: > This guy looks into the > instance's dictionary for the name, Yes. > if not found then looks into the > parent class's dictionary, You mean : the class's dictionnary. > if not found searches the base classes, if > not found checks __getattr__, and invoke it if found > still not found raises an > AttributeError. > Does this look right? Given the above corrections, mostly, yes. Note that the first one already makes a big difference. Also, it doesn't take into accounts __slots__ and descriptors. Let's ignore slots for the moment - we still have descriptors (property, functions, and other computed attributes), which have their __get__ method invoked when looked up. > If not, are these attribute lookup rules > documented somewhere? I have not been paying much attention to the > new style classes, have things changed with the introduction of these > new style classes? Well, yes, somewhat. Else we wouldn't have them, isn't it ? Anyway, wrt/ your problem, wether you use old-style or new-style classes won't make much difference: hooking into Body's instances attribute lookup won't let you trace attribute lookup on objects that are themselves attributes of a Body instance (hmmm, not very clear, sorry...re-reading it slowly, it should make sens. Hopefully...). -- http://mail.python.org/mailman/listinfo/python-list
