Good use for itertools.dropwhile and itertools.takewhile
neilc at norwich.edu
Wed Dec 5 15:34:37 CET 2012
On 2012-12-05, Chris Angelico <rosuav at gmail.com> wrote:
> On Wed, Dec 5, 2012 at 12:17 PM, Nick Mellor <thebalancepro at gmail.com> wrote:
>> takewhile mines for gold at the start of a sequence, dropwhile
>> drops the dross at the start of a sequence.
> When you're using both over the same sequence and with the same
> condition, it seems odd that you need to iterate over it twice.
> Perhaps a partitioning iterator would be cleaner - something
> like this:
> def partitionwhile(predicate, iterable):
> iterable = iter(iterable)
> while True:
> val = next(iterable)
> if not predicate(val): break
> yield val
> raise StopIteration # Signal the end of Phase 1
> for val in iterable: yield val # or just "yield from iterable", I think
> Only the cold hard boot of reality just stomped out the spark
> of an idea. Once StopIteration has been raised, that's it,
> there's no "resuming" the iterator. Is there a way around that?
> Is there a clean way to say "Done for now, but next time you
> ask, there'll be more"?
> I tested it on Python 3.2 (yeah, time I upgraded, I know).
Well, shoot! Then this is a job for groupby, not takewhile.
"""split s into product name and product description.
>>> prod_desc("CAR FIFTY TWO Chrysler LeBaron.")
['CAR FIFTY TWO', 'Chrysler LeBaron.']
>>> prod_desc("MR. JONESEY Saskatchewan's finest")
['MR. JONESEY', "Saskatchewan's finest"]
>>> prod_desc("no product name?")
['', 'no product name?']
>>> prod_desc("NO DESCRIPTION")
['NO DESCRIPTION', '']
prod = ''
desc = ''
for k, g in itertools.groupby(s.split(),
key=lambda w: any(c.islower() for c in w)):
a = ' '.join(g)
desc = a
prod = a
return [prod, desc]
This has no way to preserve odd white space which could break
evil product name differences.
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