[Python-ideas] Statements vs Expressions... why?

[Cliff Wells]

On Tue, 2008-09-16 at 13:06 +1200, Greg Ewing wrote:
> Cliff Wells wrote:
> 
> > s = 'abc'
> > x = for c in s: YIELD c     # x = 'a', 'b', 'c'
> 
> You mean that the value of (for c in s: YIELD c) is
> a tuple? Or that it's an iterator that produces that
> series of values?

The latter, although I admit not seeing the importance of the
distinction in this case.

> > I = [ 'spam', 'eggs' ]
> > 
> > for J in I:                 # J = 'spam' then 'eggs'
> >     YIELD (                 # evaluate to an iterable
> >         for j in J: YIELD j # j is 's' then 'p' then ...
> >     )
>  >
>  > so we get '-'.join( 's','p','a','m','e','g','g','s' )
> 
> I'm still not getting a clear idea of what semantics
> you intend for a for-loop-with-YIELD. Neither of the
> interpretations I suggested above (sequence or iterator)
> seems to produce this result.
> 
> > maybe this is clearer as
> > 
> > for J in I: 
> >     tmp = for j in J: YIELD j
> >     YIELD tmp
> 
> No, that's not any clearer. Can you provide a translation
> into current, valid Python?

My example was a translation of Arnaud's challenge:

    I = ['spam', 'eggs']
    def flatten(I):
         for J in I:
             for j in J:
                 yield j

     >>> '-'.join(flatten(['spam', 'eggs']))
     's-p-a-m-e-g-g-s'


It's possible there's a nuance you're seeing that I'm not (and
unfortunately we can't test).  What are you predicting as the output?

Cliff