python3: 'where' keyword

[Paul Rubin]

Nick Coghlan <ncoghlan at iinet.net.au> writes:
> > Usage could be something like:
> >  >>> res = [ f(i) for i in objects ] where:
> >  >>>     def f(x):
> >  >>>         #do something
> 
> Hmm, this is actually a really interesting idea. Avoiding accidental
> namespace conflicts is certainly one of the advantages of using lambdas.

I like it too.  Seems a little perl-ish, but what the hey.

> In fact, any subexpressions in a complicated expression can be
> extracted and named for clarity without fear of screwing up the
> containing namespace, which would be an enormous boon for software
> maintainers.

Sure, why not:

    x = (-b + sqrt(discriminant))/(2*a) where:
          discriminant = b*b - 4*a*c

Maybe you could just have a where: suite that binds variables
within the suite:

    where:
       def f(x):
          #do something
    res = [ f(i) for i in objects ]

    where:
       discriminant = b*b - 4*a*c
    x = (-b + sqrt(discriminant))/(2*a) 

Syntax is
   where:
      suite
   statement

the suite has its own scope so any variable created there is local to
the suite plus the following statement.  The scope vanishes after the
statement.