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

Groups > comp.lang.python > #90849

Re: Slices time complexity

X-FeedAbuse http://nntpfeed.proxad.net/abuse.pl feeded by 78.192.65.63
Path csiph.com!usenet.pasdenom.info!nntpfeed.proxad.net!news.muarf.org!news.roellig-ltd.de!open-news-network.org!border2.nntp.ams1.giganews.com!border1.nntp.ams1.giganews.com!nntp.giganews.com!newsfeed.xs4all.nl!newsfeed2.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
Return-Path <rosuav@gmail.com>
X-Original-To python-list@python.org
Delivered-To python-list@mail.python.org
X-Spam-Status OK 0.000
X-Spam-Evidence '*H*': 1.00; '*S*': 0.00; 'python.': 0.02; 'value,': 0.04; 'model,': 0.05; '*not*': 0.07; 'memory.': 0.07; 'referring': 0.07; 'transform': 0.07; 'explanation': 0.09; 'pointers': 0.09; 'references,': 0.09; 'cc:addr:python-list': 0.11; 'python': 0.11; '"python': 0.16; 'behaviour.': 0.16; 'chris,': 0.16; 'cons': 0.16; 'elements,': 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'lisp': 0.16; 'objects.': 0.16; 'play.': 0.16; 'pointers,': 0.16; 'semantics': 0.16; 'storing': 0.16; 'subscripting': 0.16; 'variable.': 0.16; 'prevent': 0.16; ':-)': 0.16; 'wrote:': 0.18; '(but': 0.19; 'pointed': 0.19; "python's": 0.19; 'value.': 0.19; '>>>': 0.22; 'cc:addr:python.org': 0.22; 'either.': 0.24; 'integer': 0.24; 'pointer': 0.24; 'cc:2**0': 0.24; 'references': 0.26; 'pass': 0.26; 'post': 0.26; 'header:In- Reply-To:1': 0.27; 'idea': 0.28; 'function': 0.29; 'specifically': 0.29; 'chris': 0.29; "doesn't": 0.30; 'said,': 0.30; 'message- id:@mail.gmail.com': 0.30; 'code': 0.31; "d'aprano": 0.31; 'helpful.': 0.31; 'pascal': 0.31; 'steven': 0.31; 'another': 0.32; 'programmers': 0.33; 'subject:time': 0.33; 'copying': 0.34; 'sense': 0.34; 'could': 0.34; 'something': 0.35; 'but': 0.35; 'received:google.com': 0.35; 'really': 0.36; 'fun,': 0.36; 'similar': 0.36; 'example,': 0.37; 'virtual': 0.37; 'being': 0.38; 'sometimes': 0.38; 'pm,': 0.38; 'rather': 0.38; 'anything': 0.39; 'explain': 0.39; 'itself': 0.39; 'though,': 0.39; 'skip:p 20': 0.39; 'how': 0.40; 'even': 0.60; 'most': 0.60; 'simply': 0.61; "you're": 0.61; 'first': 0.61; 'different': 0.65; 'talking': 0.65; 'between': 0.67; 'it!': 0.67; 'equals': 0.68; 'fact,': 0.69; '2015': 0.84; 'hardly': 0.84; 'to:none': 0.92; 'differences': 0.93
DKIM-Signature v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:cc :content-type; bh=WzOFX455vbzK899TU9HkGff1EYxm45/FRPdgT+Gc5So=; b=N5aipTJ+MF1TVjSprP08TNtGT9yoRCKbBJQ3bRA3+Z+yjXGvp3ssBU3ZD6Ns/Q6HHP vUz1OOlzymkCccP21XfKamxZDyHp04Re4ZLHmyOmI1oG7z+yMk93IzRjBg9d2Z+canFO p2pXVXs/zVPp6RG9tvKSNOOqMOR7Wy2cNBU8qQzEbSFKXQHkSfqUeQnTCuiYJvVXPxNZ oLpy/Kdynsm7zaYHhTQP9yMdHtwYPnIXgEXcAIlrfiDeZCWjzxxHG2585PlIia/QccL4 UTruTTCPF+zib8rrIQWBcMGgCHYmSrYL7ksAeVLoY3A14JJSNvEO0nsGPSt+dEwx6jQt 0EBQ==
MIME-Version 1.0
X-Received by 10.107.134.153 with SMTP id q25mr21687307ioi.27.1432041887940; Tue, 19 May 2015 06:24:47 -0700 (PDT)
In-Reply-To <555b2fa9$0$12996$c3e8da3$5496439d@news.astraweb.com>
References <9ceklad15llnv3npejq9iuh91soci8aeqo@4ax.com> <mailman.114.1431978628.17265.python-list@python.org> <7ea01590-a559-46e5-abf5-29622e39aae7@googlegroups.com> <555ac697$0$12910$c3e8da3$5496439d@news.astraweb.com> <862693ca-42cf-4f5b-ac12-133e43e7606b@googlegroups.com> <878uclf3bt.fsf@elektro.pacujo.net> <555af171$0$12995$c3e8da3$5496439d@news.astraweb.com> <874mn9ezaw.fsf@elektro.pacujo.net> <mailman.124.1432025439.17265.python-list@python.org> <555b2fa9$0$12996$c3e8da3$5496439d@news.astraweb.com>
Date Tue, 19 May 2015 23:24:47 +1000
Subject Re: Slices time complexity
From Chris Angelico <rosuav@gmail.com>
Cc "python-list@python.org" <python-list@python.org>
Content-Type text/plain; charset=UTF-8
X-BeenThere python-list@python.org
X-Mailman-Version 2.1.20+
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.134.1432041891.17265.python-list@python.org> (permalink)
Lines 53
NNTP-Posting-Host 2001:888:2000:d::a6
X-Trace 1432041891 news.xs4all.nl 2905 [2001:888:2000:d::a6]:55142
X-Complaints-To abuse@xs4all.nl
Xref csiph.com comp.lang.python:90849

Show key headers only | View raw

On Tue, May 19, 2015 at 10:42 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> On Tue, 19 May 2015 06:50 pm, Chris Angelico wrote:
>
>> On Tue, May 19, 2015 at 6:39 PM, Marko Rauhamaa <marko@pacujo.net> wrote:
>>> For example, you could explain Python's object references as pointers
>>> (memory addresses) if you considered that helpful. (That's how Lisp
>>> textbooks often explain cons cells.)
>>
>> Sorta-kinda-maybe, but if a C programmer's idea of pointers is invoked
>> to explain Python's object references, the differences will start to
>> be problematic:
>>
>> 1) Pointer arithmetic simply doesn't exist in Python. Arrays/lists are
>> not just pointers to their first elements, and subscripting is most
>> definitely NOT "add to pointer and dereference".
>> 2) In fact, dereferencing as a whole isn't really a 'thing' either. At
>> best, it happens automatically.
>> 3) References actually mean something. Copying a pointer doesn't.
>> Whether the Python you're using is refcounted (CPython) or
>> mark-and-sweep (uPy, I think) or some other model, an additional
>> reference to the same object will prevent it from being disposed of,
>> which isn't the case in C.
>> 4) A pointer is itself a value. You can pass a
>> pointer-to-local-variable to another function and have that function
>> change a local variable.
>> 5) Furthermore, since a pointer is a value, you can have pointers to
>> pointers, etc. Doesn't make any sense in Python.
>
> Chris, that is one of the best explanations for why "references equals
> pointers" is *not* a good explanation for Python's behaviour. I may have to
> steal it :-)

:) They say that turnabout is fair play. I stole your "Python vs
MATLAB" python-tutor post about call-by-value vs call-by-reference vs
object semantics for years (until some other pages picked up the same
content). Go for it!

That said, though, I was specifically referring to C's pointer
semantics. As Gregory pointed out, Pascal has rather different pointer
semantics; but if you're talking about Python references and
considering using any concept of object addressing and pointers, it's
most likely going to be something similar to C/assembly, where a
pointer is a dereferenceable integer storing an offset into memory.

(But don't even get *started* on near vs far pointers, code vs data
segments and the thunks required to transform between them,
memory-mapped disk, virtual segments, overlapping segments, shared
memory, memory-mapped I/O, and all those other things that C
programmers sometimes contend with. Fun, but hardly anything to do
with Python objects. :) )

ChrisA

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

Thread

Slices time complexity Mario Figueiredo <marfig@gmail.com> - 2015-05-18 20:23 +0100
  Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-19 05:36 +1000
    Re: Slices time complexity Mario Figueiredo <marfig@gmail.com> - 2015-05-18 20:49 +0100
      Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-19 06:04 +1000
  Re: Slices time complexity Todd <toddrjen@gmail.com> - 2015-05-18 21:42 +0200
  Re: Slices time complexity Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-18 13:49 -0600
    Re: Slices time complexity Fabien <fabien.maussion@gmail.com> - 2015-05-18 21:54 +0200
      Re: Slices time complexity Todd <toddrjen@gmail.com> - 2015-05-18 22:23 +0200
    Re: Slices time complexity Mario Figueiredo <marfig@gmail.com> - 2015-05-18 22:04 +0100
      Re: Slices time complexity Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-18 22:38 +0100
      Re: Slices time complexity Terry Reedy <tjreedy@udel.edu> - 2015-05-18 19:04 -0400
    Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-18 19:20 -0700
      Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 15:13 +1000
        Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-18 22:33 -0700
          Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-19 10:12 +0300
            Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 18:16 +1000
              Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-19 11:39 +0300
                Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-19 18:50 +1000
                Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-19 12:35 +0300
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 23:44 +1000
                Re: Slices time complexity Christian Gollwitzer <auriocus@gmx.de> - 2015-05-20 23:54 +0200
                Re: Slices time complexity Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-19 23:00 +1200
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 11:47 +1000
                Re: Slices time complexity Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-05-20 08:07 -0400
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 22:42 +1000
                Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-19 23:24 +1000
                Re: Slices time complexity Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-20 12:31 +1200
                Re: Slices time complexity Ben Finney <ben+python@benfinney.id.au> - 2015-05-20 10:42 +1000
                Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-20 07:24 +0300
                Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 21:30 -0700
                Re: Slices time complexity Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-20 06:06 +0100
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 15:57 +1000
                Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-20 09:17 +0300
                Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 23:23 -0700
                Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-20 09:46 +0300
                Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-20 00:03 -0700
                Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-20 10:45 +0300
                List semantics [was Re: Slices time complexity] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 17:23 +1000
                Re: List semantics [was Re: Slices time complexity] Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-20 20:54 +1200
                Re: List semantics [was Re: Slices time complexity] Ned Batchelder <ned@nedbatchelder.com> - 2015-05-20 04:08 -0700
                Re: List semantics [was Re: Slices time complexity] Terry Reedy <tjreedy@udel.edu> - 2015-05-20 14:42 -0400
                Re: List semantics [was Re: Slices time complexity] Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-05-21 11:06 +1200
                Re: List semantics [was Re: Slices time complexity] Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-21 12:10 +1000
                Re: Slices time complexity "Bartc" <bartc@freeuk.com> - 2015-05-20 10:56 +0100
                Re: Slices time complexity Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-05-20 10:16 +0100
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-21 15:19 +1000
                Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-21 09:20 +0300
                Re: Slices time complexity bartc <bart4858@gmail.com> - 2015-05-21 06:34 -0700
                Re: Slices time complexity MRAB <python@mrabarnett.plus.com> - 2015-05-21 17:50 +0100
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-22 03:16 +1000
                Re: Slices time complexity bart4858@gmail.com - 2015-05-21 12:48 -0700
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 12:26 +1000
                Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-20 12:36 +1000
                Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 20:02 -0700
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 21:43 +1000
                Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-19 18:59 +0300
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 03:46 +1000
                Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-20 04:12 +1000
                Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-19 21:19 +0300
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 10:43 +1000
                Re: Slices time complexity Marko Rauhamaa <marko@pacujo.net> - 2015-05-20 07:30 +0300
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 15:33 +1000
                Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 15:58 +1000
                Re: Slices time complexity Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-05-19 15:18 +0100
            Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 04:46 -0700
              Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 05:14 -0700
          Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 18:19 +1000
            Re: Slices time complexity Rustom Mody <rustompmody@gmail.com> - 2015-05-19 04:41 -0700
  Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-19 19:45 +1000
    Re: Slices time complexity Serhiy Storchaka <storchaka@gmail.com> - 2015-05-19 13:15 +0300
    Re: Slices time complexity Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2015-05-19 12:09 +0100
    Re: Slices time complexity "Bartc" <bartc@freeuk.com> - 2015-05-19 15:52 +0100
      Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-20 03:07 +1000
        Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-20 03:19 +1000
        Re: Slices time complexity Mario Figueiredo <marfig@gmail.com> - 2015-05-20 20:51 +0100
          Re: Slices time complexity Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-20 14:33 -0600
          Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-21 06:35 +1000
          Re: Slices time complexity Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-20 21:47 +0100
            Re: Slices time complexity Mario Figueiredo <marfig@gmail.com> - 2015-05-20 22:23 +0100
          Re: Slices time complexity Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-21 17:35 +1000
            Re: Slices time complexity Chris Angelico <rosuav@gmail.com> - 2015-05-21 18:25 +1000
    Re: Slices time complexity Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-19 09:15 -0600
    Re: Slices time complexity Serhiy Storchaka <storchaka@gmail.com> - 2015-05-19 22:51 +0300

csiph-web