Paul Rubin wrote:
> Peter Otten <[EMAIL PROTECTED]> writes:
>> > all_heights = (block.height for block in stack if
>> > block.is_marked()) if is_empty(all_heights):
>> > raise SomeError("No marked block")
>>
>> Such a function would have to rebind the generator:
>
> Yeah, that's what I mean about generators not working the right way.
>
>> You can make it work, but the result tends to be messy:
>
> I think it's better underneath, but still syntactically ugly, to just
> defer the generator creation:
>
> all_heights = lambda:
> (block.height for block in stack if
> block.is_marked())
You still need the stop() trick to omit the heights after the marked block.
> if is_empty(all_heights ()):
> raise SomeError("No marked block")
> height = sum(all_heights ())
>
> Now sum and is_empty see two separate generators, so is_empty is
> straightforward:
>
> def is_empty(gen):
> try:
> gen.next()
> return True
> except StopIteration:
> return False
Alternatively you can turn all_heights into a list (comprehension) which
makes the test trivial.
I think it will be interesting to see how Python 3000's emphasis on
iterators will affect overall code complexity.
Peter
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