What other languages use the same data model as Python?

[Terry Reedy]

On 5/10/2011 3:41 AM, Gregory Ewing wrote:

> Actually, you're right. What I've presented is a paper-and-pencil
> implementation of the Python data model. Together with a set of
> rules for manipulating the diagram under the direction of Python
> code, you have a complete implementation of Python that you can
> execute in your head.

I think that it would be both fun and useful to have an animated 
graphical tutorial that used and box and arrow model. Names should be in 
ovals (instead of the little boxes used here due to text limitations) to 
differentiate them from objects. Immutable objects could have solid 
boundaries and mutables a broken line boundary. Collection objects would 
have dotted lines to separate slots. Ovals could also use different 
lines for builtins, globals, and locals.

> And you NEED such an implementation in order to reason correctly
> about Python programs under all circumstances.
>
> I find it very difficult to imagine *any* implementation of
> Python, computer-based or otherwise, that doesn't have something
> equivalent to references. Whether you call them that, or pointers,
> or arrows, or object bindings, or something else, the concept
> needs to be there in some form.

Since namespaces link names in a namespace with objects not in the 
namespace, any practical implementation needs a third entity to link or 
associated each name with an object. This is pretty much needed to 
explain multiple links without objects being in multiple locations. It 
is also needed to explain how an object can link to itself.

-- 
Terry Jan Reedy