[Python-Dev] Explicit Lexical Scoping (pre-PEP?)

[Guido van Rossum]

On 7/5/06, Michael Chermside <mcherm at mcherm.com> wrote:
> Guido writes:
>    [discussion of how to fix the can't-bind-outer-scope-vars wart]
> > I think we have to continue to search for a solution that extends the
> > idea of global declarations.
> >
> > I've proposed extending its meaning to refer to the nearest outer
> > scope where the variable is set; if there is no such scope it's an
> > error. This will break a small number of program but probably not very
> > many; still, it'll require a future statement or waiting until Python
> > 3.0. The downside is that "global" is not a very intuitive word for
> > this new meaning.
>
> I disagree with your last statement -- I think "global" _is_ a very
> intuitive word for this. As I understand it, in programming "global"
> has two meanings, closely intertwined. One is "universal, same
> throughout the system". For instance, "The singleton pattern is used
> to create a single, global instance of a type." The second meaning is
> the term "global variable". This term developed (I believe) in
> languages that had only two scopes: local-to-current-function and
> global-to-entire-program. But the term "global variable" refers to
> any variable whose assignment is a "side effect", regardless of
> whether that variable is global-to-entire-program, global-to-module,
> or even global-to-enclosing-function. I have even heard the term
> "global variable" (mis)used to refer to any kind of side effect.
>
> Anyhow, in Python only builtins is _really_ global -- even today's
> global keyword only refers to module scope. So I believe that it
> would be a very reasonable interpretation of "global" to mean
> "not local", and implement as "search enclosing scopes in order
> to find the binding".

I really wish I could agree with you, because that would make the
choice so much easier.

However I still don't believe "global" has the stretchiness in its
meaning that you claim it has. Have you ever heard a Python programmer
talking about closures use the word "global variable"?

Are there any other native speakers who side with Michael?

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)