[Python-ideas] Where-statement (Proposal for function expressions)

[Jim Jewett]

On Thu, Jul 16, 2009 at 8:04 PM, Jan Kaliszewski<zuo at chopin.edu.pl> wrote:

> ... I don't see any reasonable *semantics* of
> return or yield within where-block in proposed form.

next_batch = myfilter(candidates, failed) where:
    failed=[]
    for x in this_batch:
        if magical(x):
            # We actually found one!!!
            return x
        # more failures, of course.
        # bias the next batch to a different section
        # of the search space.
        failed.append(x)

I leave to others the judgment on whether or not any function
containing code is already too long...

alternatively,

provide(foo(item)) where:
    start_to_generate_an_item()
    if flag():
        # Are there reasons to return instead of throwing?
        raise HigherPriority
    item=finish_generation()

Again, I'm not certain that the style should be encouraged, but
neither I am sure it shouldn't be.

-jJ