Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #34300

Re: Good use for itertools.dropwhile and itertools.takewhile

Path csiph.com!usenet.pasdenom.info!aioe.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed4.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
Return-Path <python@mrabarnett.plus.com>
X-Original-To python-list@python.org
Delivered-To python-list@mail.python.org
X-Spam-Status OK 0.002
X-Spam-Evidence '*H*': 1.00; '*S*': 0.00; 'that?': 0.05; 'val': 0.07; 'iterate': 0.09; 'raised,': 0.09; 'def': 0.10; 'dec': 0.15; 'cleaner': 0.16; 'from:addr:mrabarnett.plus.com': 0.16; 'from:addr:python': 0.16; 'from:name:mrab': 0.16; 'iterable': 0.16; 'iterable:': 0.16; 'iterator': 0.16; 'iterator.': 0.16; 'message-id:@mrabarnett.plus.com': 0.16; 'nick': 0.16; 'object()': 0.16; 'partitioning': 0.16; 'received:84.93': 0.16; 'received:84.93.230': 0.16; 'sequence,': 0.16; 'sequence.': 0.16; 'true:': 0.16; 'twice.': 0.16; 'wed,': 0.16; 'wrote:': 0.17; 'odd': 0.17; 'yield': 0.17; 'skip:" 30': 0.20; 'subject:skip:i 10': 0.22; 'this:': 0.23; 'seems': 0.23; 'raise': 0.24; 'header :In-Reply-To:1': 0.25; 'header:User-Agent:1': 0.26; 'skip:" 20': 0.26; 'chris': 0.28; 'received:192.168.1.3': 0.29; 'skip:_ 10': 0.29; 'class': 0.29; 'received:84': 0.32; 'could': 0.32; 'to:addr :python-list': 0.33; 'fresh': 0.35; 'sequence': 0.35; 'pm,': 0.35; 'something': 0.35; 'there': 0.35; 'next': 0.35; 'but': 0.36; 'skip:p 20': 0.36; 'item': 0.37; 'subject:: ': 0.38; 'some': 0.38; 'description': 0.39; 'to:addr:python.org': 0.39; 'received:192': 0.39; 'received:192.168': 0.40; 'end': 0.40; 'think': 0.40; 'red': 0.60; 'kind': 0.61; 'skip:n 10': 0.63; 'header:Reply-To:1': 0.68; 'reply-to:no real name:2**0': 0.72; 'ask,': 0.84; 'object:': 0.84; 'reply-to:addr:python.org': 0.84; 'drops': 0.91; 'subject:Good': 0.91
X-CM-Score 0.00
X-CNFS-Analysis v=2.0 cv=BusfMPr5 c=1 sm=1 a=0nF1XD0wxitMEM03M9B4ZQ==:17 a=O2Kvzccb_dQA:10 a=2HYzhsMY58wA:10 a=ihvODaAuJD4A:10 a=OUOv7kDek9cA:10 a=8nJEP1OIZ-IA:10 a=EBOSESyhAAAA:8 a=8AHkEIZyAAAA:8 a=8qMxVT5i32MA:10 a=pGLkceISAAAA:8 a=Mp2tdt9SQ3vPMpyuRmAA:9 a=wPNLvfGTeEIA:10 a=MSl-tDqOz04A:10 a=0nF1XD0wxitMEM03M9B4ZQ==:117
X-AUTH mrabarnett:2500
Date Wed, 05 Dec 2012 17:57:19 +0000
From MRAB <python@mrabarnett.plus.com>
User-Agent Mozilla/5.0 (Windows NT 5.1; rv:17.0) Gecko/17.0 Thunderbird/17.0
MIME-Version 1.0
To python-list@python.org
Subject Re: Good use for itertools.dropwhile and itertools.takewhile
References <b80f3ab3-ef81-4806-86db-efd5800d4bb3@googlegroups.com> <mailman.474.1354653865.29569.python-list@python.org> <05bca175-2077-4fb8-917e-baee1a43a47d@googlegroups.com> <CAPTjJmrHAu=FtC2V=TN0WkxNbzpJx5CgdAm4J6N9C_1ZDR4Ehg@mail.gmail.com>
In-Reply-To <CAPTjJmrHAu=FtC2V=TN0WkxNbzpJx5CgdAm4J6N9C_1ZDR4Ehg@mail.gmail.com>
Content-Type text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding 7bit
X-BeenThere python-list@python.org
X-Mailman-Version 2.1.15
Precedence list
Reply-To python-list@python.org
List-Id General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe <http://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive <http://mail.python.org/pipermail/python-list/>
List-Post <mailto:python-list@python.org>
List-Help <mailto:python-list-request@python.org?subject=help>
List-Subscribe <http://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups comp.lang.python
Message-ID <mailman.508.1354730246.29569.python-list@python.org> (permalink)
Lines 68
NNTP-Posting-Host 2001:888:2000:d::a6
X-Trace 1354730246 news.xs4all.nl 6879 [2001:888:2000:d::a6]:44668
X-Complaints-To abuse@xs4all.nl
Xref csiph.com comp.lang.python:34300

Show key headers only | View raw

On 2012-12-05 13:45, Chris Angelico wrote:
> On Wed, Dec 5, 2012 at 12:17 PM, Nick Mellor <thebalancepro@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"?
>
Perhaps you could have some kind of partitioner object:

class Partitioner:
     _SENTINEL = object()

     def __init__(self, iterable):
         self._iterable = iter(iterable)
         self._unused_item = self._SENTINEL

     def takewhile(self, condition):
         if self._unused_item is not self._SENTINEL:
             if not condition(self._unused_item):
                 raise StopIteration

             yield self._unused_item
             self._unused_item = self._SENTINEL

         for item in self._iterable:
             if not condition(item):
                 self._unused_item = item
                 break

             yield item

         raise StopIteration

     def remainder(self):
         if self._unused_item is not self._SENTINEL:
             yield self._unused_item
             self._unused_item = self._SENTINEL

         for item in self._iterable:
             yield item

         raise StopIteration

def is_all_caps(word):
     return word == word.upper()

part = Partitioner("CAPSICUM RED fresh from QLD".split())
product = " ".join(part.takewhile(is_all_caps))
description = " ".join(part.remainder())
print([product, description])

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Good use for itertools.dropwhile and itertools.takewhile Nick Mellor <thebalancepro@gmail.com> - 2012-12-04 05:57 -0800
  Re: Good use for itertools.dropwhile and itertools.takewhile Neil Cerutti <neilc@norwich.edu> - 2012-12-04 14:23 +0000
    Re: Good use for itertools.dropwhile and itertools.takewhile Nick Mellor <thebalancepro@gmail.com> - 2012-12-04 06:47 -0800
      Re: Good use for itertools.dropwhile and itertools.takewhile Neil Cerutti <neilc@norwich.edu> - 2012-12-04 15:17 +0000
  Re: Good use for itertools.dropwhile and itertools.takewhile Vlastimil Brom <vlastimil.brom@gmail.com> - 2012-12-04 15:31 +0100
    Re: Good use for itertools.dropwhile and itertools.takewhile Nick Mellor <thebalancepro@gmail.com> - 2012-12-04 07:24 -0800
      Re: Good use for itertools.dropwhile and itertools.takewhile Vlastimil Brom <vlastimil.brom@gmail.com> - 2012-12-04 22:08 +0100
    Re: Good use for itertools.dropwhile and itertools.takewhile Nick Mellor <thebalancepro@gmail.com> - 2012-12-04 07:24 -0800
      Re: Good use for itertools.dropwhile and itertools.takewhile Neil Cerutti <neilc@norwich.edu> - 2012-12-04 18:26 +0000
  Re: Good use for itertools.dropwhile and itertools.takewhile Alexander Blinne <news@blinne.net> - 2012-12-04 18:18 +0100
    Re: Good use for itertools.dropwhile and itertools.takewhile DJC <djc@news.invalid> - 2012-12-04 18:28 +0000
      Re: Good use for itertools.dropwhile and itertools.takewhile Alexander Blinne <news@blinne.net> - 2012-12-04 19:48 +0100
        Re: Good use for itertools.dropwhile and itertools.takewhile Ian Kelly <ian.g.kelly@gmail.com> - 2012-12-04 12:37 -0700
          Re: Good use for itertools.dropwhile and itertools.takewhile Alexander Blinne <news@blinne.net> - 2012-12-04 21:33 +0100
          Re: Good use for itertools.dropwhile and itertools.takewhile Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-12-04 21:13 +0000
        Re: Good use for itertools.dropwhile and itertools.takewhile MRAB <python@mrabarnett.plus.com> - 2012-12-04 20:17 +0000
  Re: Good use for itertools.dropwhile and itertools.takewhile Terry Reedy <tjreedy@udel.edu> - 2012-12-04 15:44 -0500
    Re: Good use for itertools.dropwhile and itertools.takewhile Nick Mellor <thebalancepro@gmail.com> - 2012-12-04 17:17 -0800
      Re: Good use for itertools.dropwhile and itertools.takewhile Chris Angelico <rosuav@gmail.com> - 2012-12-06 00:45 +1100
        Re: Good use for itertools.dropwhile and itertools.takewhile Neil Cerutti <neilc@norwich.edu> - 2012-12-05 14:34 +0000
          Re: Good use for itertools.dropwhile and itertools.takewhile Ian Kelly <ian.g.kelly@gmail.com> - 2012-12-05 08:33 -0700
            Re: Good use for itertools.dropwhile and itertools.takewhile Neil Cerutti <neilc@norwich.edu> - 2012-12-05 16:11 +0000
      Re: Good use for itertools.dropwhile and itertools.takewhile Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-12-05 15:32 +0000
      Re: Good use for itertools.dropwhile and itertools.takewhile Ian Kelly <ian.g.kelly@gmail.com> - 2012-12-05 09:16 -0700
      Re: Good use for itertools.dropwhile and itertools.takewhile MRAB <python@mrabarnett.plus.com> - 2012-12-05 17:57 +0000
    Re: Good use for itertools.dropwhile and itertools.takewhile Nick Mellor <thebalancepro@gmail.com> - 2012-12-04 17:17 -0800
      Re: Good use for itertools.dropwhile and itertools.takewhile Neil Cerutti <neilc@norwich.edu> - 2012-12-05 13:29 +0000
        Re: Good use for itertools.dropwhile and itertools.takewhile Nick Mellor <thebalancepro@gmail.com> - 2012-12-05 09:04 -0800
          Re: Good use for itertools.dropwhile and itertools.takewhile MRAB <python@mrabarnett.plus.com> - 2012-12-05 17:57 +0000
          Re: Good use for itertools.dropwhile and itertools.takewhile Neil Cerutti <neilc@norwich.edu> - 2012-12-05 18:16 +0000
            Re: Good use for itertools.dropwhile and itertools.takewhile Nick Mellor <thebalancepro@gmail.com> - 2012-12-05 11:01 -0800
              Re: Good use for itertools.dropwhile and itertools.takewhile Neil Cerutti <neilc@norwich.edu> - 2012-12-05 20:13 +0000
              Re: Good use for itertools.dropwhile and itertools.takewhile Vlastimil Brom <vlastimil.brom@gmail.com> - 2012-12-05 22:36 +0100
                Re: Good use for itertools.dropwhile and itertools.takewhile Neil Cerutti <neilc@norwich.edu> - 2012-12-06 13:06 +0000
                Re: Good use for itertools.dropwhile and itertools.takewhile Vlastimil Brom <vlastimil.brom@gmail.com> - 2012-12-06 15:12 +0100
          Re: Good use for itertools.dropwhile and itertools.takewhile Alexander Blinne <news@blinne.net> - 2012-12-06 14:40 +0100
  Re: Good use for itertools.dropwhile and itertools.takewhile Terry Reedy <tjreedy@udel.edu> - 2012-12-04 17:21 -0500
  Re: Good use for itertools.dropwhile and itertools.takewhile Paul Rubin <no.email@nospam.invalid> - 2012-12-06 13:29 -0800

csiph-web