[Python-Dev] Short-circuiting iterators

[Raymond Hettinger]

[Matthew F. Barnes]
> The ability to remotely terminate a for-loop also struck me as
somewhat
> interesting:
> 
>     def estimate(item, iterable):
>         . . .
>         if good_enough:
>             iterable.stop()
>             return result
> 
>     for x in iterable:
>         . . .
>         approx *= estimate(x, iterable)

Good inspiration; wrong technique.  For the RightWay(tm), try a
functional approach composing a target calculation with a function
generating successively more accurate approximations and a consumer
function that stops when the desired accuracy is achieved.  The idea is
to decouple the steps into side-effect-free, reusable components.  For a
worked-out, comprehensive example, see
http://www.md.chalmers.se/~rjmh/Papers/whyfp.pdf .


> But these are highly contrived and hardly compelling.

That suggests an answer to your earlier question as to whether
itertools.interruptable(iterable) would be a useful addition ;-)



Raymond