[Python-Dev] Pre-PEP: Attribute Access Handlers v2

Gordon McMillan gmcm@hypernet.com
Fri, 21 Jul 2000 15:58:20 -0400

Paul Prescod  wrote:

> Performance is only one of the goals. Clarity is the more major
> one. Safety is another. When you start combining __getattr__ with
> multiply inherited base class __getattr__ and so forth you get
> into a real mess. This proposal does not have that problem.

You're doing some obsfucating here. Overriding a method with 
multiple base class implementations of that method with the 
desire to chain to one or more of the base class 
implementations of that method is a mess. It's not more of a 
mess because the method is named __getattr__. The obvious 
solution has nothing to do with the language - it's to use has-a 
instead of is-a.

This proposal changes those semantics. Hooking an attribute 
masks anything in a base class with that name. That's 
probably a good thing, but it should be made explicit since 
that's not the way __getattr__ behaves.

Similarly, there's a difference from __setattr__. If you assign to 
the instance.__dict__, the hook will no longer apply for that 
instance / attribute.

Also note that while this is *safer* than __xxxattr__, it's still 
not *safe*. Infinite recursion is less likely, but still easily 
Truth-in-PEPs-ly y'rs

- Gordon