[Python-Dev] re: LANL syntax (case/branch)

[gvwilson@nevex.com]

> > Greg Wilson wrote:
> > One student (a physicist who now does computer graphics) sent me:
> > 
> >         if x is:
> >             expr1, expr2:
> >                 code using x (which is either val1 or val2)
> >             expr3:
> >                 code using x (which is guaranteed to be val3)
> >             else:
> >                 code using x (which is something else)

> Ka-Ping Yee wrote:
> I like this quite a lot! One question: in that last "else" clause,
> wouldn't "x" be undefined?

(Quick flip through notes): "x is None in the else branch".

Looking at it again, it came up as part of the question "Why isn't
assignment an operator?"  The student in question was used to doing:

if (x = foo())
{
    body
}
else if (x = bar())
{
    body
}
else
{
    body
}

and wanted to have something in Python that would (a) provide more
flexibility than a C/C++ case statement, while (b) making it clear
that the alternatives really were mutually exclusive.

I think.  Or maybe not.  He talked really, really fast...

Greg