[Python-Dev] Type/class (original) (raw)

Steven D. Majewski sdm7g@Virginia.EDU
Fri, 11 May 2001 09:43:32 -0400 (EDT)

Catching up on this thread -- mostly because it looks like I'm going to have to use ExtensionClass to make pyobjc classes into python classes rather than types -- you can add that to the lisp of real world uses of Don's Metaclass hack that Tim
questioned.

Reading up on MetaClasses in Smalltalk again makes me appreciate the simplicity of a prototype system where everything is just an object -- all objects can be cloned, and some objects are only used for cloning -- they are the exemplars of their type which fill the role of Classes.

Unfortunately, although prototypes would be a lot simpler, it would be a pretty incompatible change for Python -- I can't think of any way to get there without a lot of breakage.

(Still -- I wonder if there's a way they could be used under the covers in the implementation to make it simpler. Prototype semantics are basically a superset of Class based semantics, which is how it was easy to do Smalltalk in Self.)

Classes are necessary for statically typed O-O languages, but IMHO, make a lot less sense for dynamic languages. If Py3K were to be a clean start, I'ld urge basing it on prototypes, but as an incremental creation -- I don't know how to get there from here (unless it could sneak in under the implementation covers!)

BTW: XlispStat, which has a prototype object system with multiple inheritence also doesn't have "super" -- there is a (call-next-method [ args... ]) function/macro which searches for the base classes. I'm sure there's a lower level function to just get the next method, but typically, call-next-method is what's used. There is no search for non-method attributes, as all of the base class instance vars are merged and made into slots of the instance itself. ( There's no class variables -- there's no classes.)

The closest python equivalent would be, as has been discussed in this thread, a super method or function that does attribute lookup on the bases.

-- Steve Majewski