Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]
Groups > comp.lang.python > #82088
| Path | csiph.com!usenet.pasdenom.info!gegeweb.org!usenet-fr.net!nerim.net!novso.com!newsfeed.xs4all.nl!newsfeed2a.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail |
|---|---|
| Return-Path | <python-python-list@m.gmane.org> |
| X-Original-To | python-list@python.org |
| Delivered-To | python-list@mail.python.org |
| X-Spam-Status | OK 0.001 |
| X-Spam-Evidence | '*H*': 1.00; '*S*': 0.00; 'that?': 0.05; 'subject:Python': 0.06; 'args)': 0.09; 'calls.': 0.09; 'pep': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'subject:using': 0.09; 'try:': 0.09; 'runs': 0.10; 'def': 0.12; 'jan': 0.12; 'agree.': 0.16; 'args:': 0.16; 'pythonic': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'reedy': 0.16; 'res': 0.16; 'rewriting': 0.16; 'roy': 0.16; 'true:': 0.16; 'unneeded': 0.16; ':-)': 0.16; 'wrote:': 0.18; 'code.': 0.18; 'bit': 0.19; '>>>': 0.22; 'putting': 0.22; 'header :User-Agent:1': 0.23; 'rid': 0.24; 'stopping': 0.24; 'gets': 0.27; 'header:X-Complaints-To:1': 0.27; 'header:In-Reply-To:1': 0.27; 'chris': 0.29; "i'm": 0.30; 'work.': 0.31; 'gives': 0.31; 'code': 0.31; 'lines': 0.31; 'controlled': 0.31; "d'aprano": 0.31; 'indentation': 0.31; 'raised': 0.31; 'seemingly': 0.31; 'steven': 0.31; 'except': 0.35; 'yield': 0.36; 'next': 0.36; 'should': 0.36; 'too': 0.37; 'two': 0.37; 'list': 0.37; 'being': 0.38; 'to:addr :python-list': 0.38; 'pm,': 0.38; 'to:addr:python.org': 0.39; 'changed': 0.39; 'received:org': 0.40; 'simple,': 0.60; 'break': 0.61; "you're": 0.61; 'kind': 0.63; 'more': 0.64; 'temporary': 0.65; 'brain': 0.68; 'smith': 0.68; 'glad': 0.83; 'received:fios.verizon.net': 0.84; 'short,': 0.84; 'wall.': 0.84; 'received:108': 0.93 |
| X-Injected-Via-Gmane | http://gmane.org/ |
| To | python-list@python.org |
| From | Terry Reedy <tjreedy@udel.edu> |
| Subject | Re: Python Iterables struggling using map() built-in |
| Date | Sun, 07 Dec 2014 19:38:08 -0500 |
| References | <004e01d01173$e1641c10$a42c5430$@gmail.com> <m61roh$i5m$1@ger.gmane.org> <CALwzid=79=i3Sez3fQYV7xU2bEAL4_ohPqxhuYj59Y5ihXk1Zg@mail.gmail.com> <mailman.16685.1417976998.18130.python-list@python.org> <5484e3d8$0$13013$c3e8da3$5496439d@news.astraweb.com> <roy-3F4751.19122007122014@news.panix.com> |
| Mime-Version | 1.0 |
| Content-Type | text/plain; charset=UTF-8; format=flowed |
| Content-Transfer-Encoding | 7bit |
| X-Gmane-NNTP-Posting-Host | pool-108-16-203-145.phlapa.fios.verizon.net |
| User-Agent | Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.6.0 |
| In-Reply-To | <roy-3F4751.19122007122014@news.panix.com> |
| X-BeenThere | python-list@python.org |
| X-Mailman-Version | 2.1.15 |
| Precedence | list |
| List-Id | General discussion list for the Python programming language <python-list.python.org> |
| List-Unsubscribe | <https://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 | <https://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.16692.1417999114.18130.python-list@python.org> (permalink) |
| Lines | 58 |
| NNTP-Posting-Host | 2001:888:2000:d::a6 |
| X-Trace | 1417999114 news.xs4all.nl 2921 [2001:888:2000:d::a6]:45759 |
| X-Complaints-To | abuse@xs4all.nl |
| Xref | csiph.com comp.lang.python:82088 |
Show key headers only | View raw
On 12/7/2014 7:12 PM, Roy Smith wrote:
> Chris Angelico wrote:
>>> I'm actually glad PEP 479 will break this kind of code. Gives a good
>>> excuse for rewriting it to be more readable.
>
> Steven D'Aprano <steve+comp.lang.python@pearwood.info> wrote:
>> What kind of code is that? Short, simple, Pythonic and elegant? :-)
>>
>> Here's the code again, with indentation fixed:
>>
>>
>> def myzip(*args):
>> iters = map(iter, args)
>> while iters:
>> res = [next(i) for i in iters]
>> yield tuple(res)
>
> Ugh. When I see "while foo", my brain says, "OK, you're about to see a
> loop which is controlled by the value of foo being changed inside the
> loop". That's not at all what's happening here, so my brain runs into a
> wall.
I agree. Too tricky. The code should have been
def myzip(*args):
if args:
iters = map(iter, args)
while True:
res = [next(i) for i in iters]
yield tuple(res)
However, this 'beautiful' code has a trap. If one gets rid of the
seemingly unneeded temporary list res by telescoping the last two lines
into a bit too much into
yield tuple(next(i) for i in iters)
we now have an infinite generator, because tuple() swallows the
StopIteration raised as a side-effect of next calls.
def myzip(*args):
if args:
iters = map(iter, args)
while True:
try:
result = [next(i) for i in iters]
except StopIteration
return
yield tuple(res)
makes the side-effect dependence of stopping clearer. Putting
yield tuple([next(i) for i in iters])
in the try would also work.
--
Terry Jan Reedy
Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread
Re: Python Iterables struggling using map() built-in Chris Angelico <rosuav@gmail.com> - 2014-12-08 05:29 +1100
Re: Python Iterables struggling using map() built-in Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-12-08 10:33 +1100
Re: Python Iterables struggling using map() built-in Chris Angelico <rosuav@gmail.com> - 2014-12-08 10:50 +1100
Re: Python Iterables struggling using map() built-in Roy Smith <roy@panix.com> - 2014-12-07 19:27 -0500
Re: Python Iterables struggling using map() built-in Chris Angelico <rosuav@gmail.com> - 2014-12-08 11:35 +1100
Re: Python Iterables struggling using map() built-in Steven D'Aprano <steve@pearwood.info> - 2014-12-08 09:40 +0000
Re: Python Iterables struggling using map() built-in Chris Angelico <rosuav@gmail.com> - 2014-12-08 20:50 +1100
Re: Python Iterables struggling using map() built-in Roy Smith <roy@panix.com> - 2014-12-08 19:02 -0500
Re: Python Iterables struggling using map() built-in Roy Smith <roy@panix.com> - 2014-12-07 19:12 -0500
Re: Python Iterables struggling using map() built-in Chris Angelico <rosuav@gmail.com> - 2014-12-08 11:34 +1100
Re: Python Iterables struggling using map() built-in Roy Smith <roy@panix.com> - 2014-12-07 19:45 -0500
Re: Python Iterables struggling using map() built-in Chris Angelico <rosuav@gmail.com> - 2014-12-08 12:00 +1100
Re: Python Iterables struggling using map() built-in MRAB <python@mrabarnett.plus.com> - 2014-12-08 03:09 +0000
Re: Python Iterables struggling using map() built-in Terry Reedy <tjreedy@udel.edu> - 2014-12-07 19:38 -0500
Re: Python Iterables struggling using map() built-in Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-12-08 18:06 +1300
Re: Python Iterables struggling using map() built-in Ned Batchelder <ned@nedbatchelder.com> - 2014-12-07 20:06 -0500
Re: Python Iterables struggling using map() built-in Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-12-09 13:50 +1100
Re: Python Iterables struggling using map() built-in Terry Reedy <tjreedy@udel.edu> - 2014-12-09 00:03 -0500
Re: Python Iterables struggling using map() built-in Steven D'Aprano <steve@pearwood.info> - 2014-12-09 06:40 +0000
Re: Python Iterables struggling using map() built-in Terry Reedy <tjreedy@udel.edu> - 2014-12-09 15:06 -0500
Re: Python Iterables struggling using map() built-in Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-12-10 11:10 +1100
Re: Python Iterables struggling using map() built-in Chris Angelico <rosuav@gmail.com> - 2014-12-10 11:20 +1100
Re: Python Iterables struggling using map() built-in Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-12-10 00:24 +0000
Re: Python Iterables struggling using map() built-in Roy Smith <roy@panix.com> - 2014-12-09 21:44 -0500
Re: Python Iterables struggling using map() built-in Steven D'Aprano <steve@pearwood.info> - 2014-12-10 09:24 +0000
Re: Python Iterables struggling using map() built-in Chris Angelico <rosuav@gmail.com> - 2014-12-10 20:32 +1100
Re: Python Iterables struggling using map() built-in Marko Rauhamaa <marko@pacujo.net> - 2014-12-10 12:58 +0200
Re: Python Iterables struggling using map() built-in Ian Kelly <ian.g.kelly@gmail.com> - 2014-12-10 09:46 -0700
Re: Python Iterables struggling using map() built-in Steven D'Aprano <steve@pearwood.info> - 2014-12-11 04:01 +0000
Re: Python Iterables struggling using map() built-in Ian Kelly <ian.g.kelly@gmail.com> - 2014-12-11 15:00 -0700
Re: Python Iterables struggling using map() built-in Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-12-12 10:28 +1100
Re: Python Iterables struggling using map() built-in Ian Kelly <ian.g.kelly@gmail.com> - 2014-12-11 16:57 -0700
Re: Python Iterables struggling using map() built-in Roy Smith <roy@panix.com> - 2014-12-11 20:55 -0500
Re: Python Iterables struggling using map() built-in Ian Kelly <ian.g.kelly@gmail.com> - 2014-12-12 00:36 -0700
Re: Python Iterables struggling using map() built-in Chris Angelico <rosuav@gmail.com> - 2014-12-12 11:44 +1100
Re: Python Iterables struggling using map() built-in Terry Reedy <tjreedy@udel.edu> - 2014-12-10 12:48 -0500
Re: Python Iterables struggling using map() built-in Ian Kelly <ian.g.kelly@gmail.com> - 2014-12-10 13:32 -0700
Re: Python Iterables struggling using map() built-in Terry Reedy <tjreedy@udel.edu> - 2014-12-10 23:17 -0500
Re: Python Iterables struggling using map() built-in Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-12-08 18:00 +1300
csiph-web