[Python-Dev] Lockstep iteration - eureka!

[Thomas Wouters]

On Wed, Aug 09, 2000 at 04:01:18PM +0100, Just van Rossum wrote:

> PEP:            1716099-3
> Title:          Index-enhanced sequence iteration
> Version:        $Revision: 1.1 $
> Owner:          Someone-with-commit-rights

I'd be willing to adopt this PEP, if the other two PEPs on my name don't
need extensive rewrites anymore.

> Features
> 
>     It adds an optional clause to the 'for' statement:
> 
>         for <index> indexing <element> in <seq>:

Ever since I saw the implementation of FOR_LOOP I've wanted this, but I
never could think up a backwards compatible and readable syntax for it ;P

> Disadvantages:

>     It will break that one person's code that uses "indexing"
>     as a variable name.

This needn't be true, if it's done in the same way as Tim proposed the 'form
from import as as as' syntax change ;)

for_stmt: 'for' exprlist [NAME exprlist] 'in' testlist ':' suite ['else' ':' suite]

If the 5th subnode of the expression is 'in', the 3rd should be 'indexing'
and the 4th would be the variable to assign the index number to. If it's
':', the loop is index-less.

(this is just a quick and dirty example; 'exprlist' is probably not the
right subnode for the indexing variable, because it can't be a tuple or
anything like that.)

-- 
Thomas Wouters <thomas@xs4all.net>

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