[Python-ideas] Variations on a loop

[Bruce Frederiksen]

Bruce Leban wrote:
>
>
> On Fri, Aug 29, 2008 at 6:19 AM, Mathias Panzenböck 
> <grosser.meister.morti at gmx.net <mailto:grosser.meister.morti at gmx.net>> 
> wrote:
>
>     Bruce Frederiksen wrote:
>     > We already have statements that only apply within loops (break and
>     > continue), how about some expressions that only apply in for loops:
>     > 'last' and 'empty':
>
>     I don't know. I don't like either. What about named loops/loop
>     objects? Using
>     this you have no need for new keywords:
>
>     myloop = for x in items:
>            result += str(x)
>            if not myloop.last:
>                    result += ', '
>     if myloop.empty:
>            result = 'no data'
>
>
> This is interesting. I don't like the fact that you have the loop 
> variable scope extending past the end of the loop and it's not clear 
> what we can do with that. It occurs to me that we can do something 
> like this without changes to the language but it's clumsy:
>
> for x in funky(items):
>     result += str(x.value)
>     if not x.last():
>         result += ', '
> else:
>     if x == funky_empty:
>         result = 'no data'
>
So x.first seems to make more sense than x.last.  You could also name 
the loops like:

outer = funky(items1)
for x in outer:
    middle = funky(items2)
    for y in middle:
        inner = funky(items3)
        for z in inner:
            middle.continue_()

It seems to implement this, funky.continue_ and funky.break_ would have 
to raise exceptions.  If the for loop honored the 'throw' method (of 
generators), it seems like this might be made to work...

-bruce