sum() vs. loop

[Steve Keller]

Christian Gollwitzer <auriocus at gmx.de> writes:

> > def sum_products(seq1, seq2):
> >      return sum([a * b for a, b in zip(seq1, seq2)])
> > def sum_products2(seq1, seq2):
> >      sum = 0
> >      for a, b in zip(seq1, seq2):
> >          sum += a * b
> >      return sum
> > [...]
>
> The first version constructs a list, sums it up and throws the list
> away, while the second version only keeps the running sum in
> memory. How about a generator expression instead, i.e.
> 
> 
>              sum((a * b for a, b in zip(seq1, seq2)))

Ah, of course.  Much cleaner and I should have seen that myself.
Thanks.

BUT

> (untested) ?

I have tested it and with () instead of [] it's even slower:

   explicit loop:   37s   ± .5s
   sum([...])       44s   ± .5s
   sum((...))       47.5s ± .5s

Now completely surprised.

Steve