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

Groups > comp.lang.python > #98447

Re: Question about math.pi is mutable

Path csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail
From Chris Angelico <rosuav@gmail.com>
Newsgroups comp.lang.python
Subject Re: Question about math.pi is mutable
Date Sun, 8 Nov 2015 23:28:00 +1100
Lines 17
Message-ID <mailman.124.1446985683.16136.python-list@python.org> (permalink)
References <mailman.77.1446804678.16136.python-list@python.org> <n1i6d4$bfg$1@dont-email.me> <mailman.90.1446826322.16136.python-list@python.org> <n1iv1c$hst$1@dont-email.me> <mailman.103.1446867842.16136.python-list@python.org> <n1kmse$p0o$1@dont-email.me> <mailman.104.1446896120.16136.python-list@python.org> <n1koqr$v63$1@dont-email.me> <mailman.105.1446898544.16136.python-list@python.org> <n1kshk$brb$1@dont-email.me> <87d1vlzy4p.fsf@elektro.pacujo.net> <878u69zxww.fsf@elektro.pacujo.net> <n1l3kd$5ma$1@dont-email.me> <563eba85$0$1611$c3e8da3$5496439d@news.astraweb.com> <n1n8mc$33l$1@dont-email.me> <87ziyowy83.fsf@elektro.pacujo.net> <n1nb0f$atn$1@dont-email.me>
Mime-Version 1.0
Content-Type text/plain; charset=UTF-8
X-Trace news.uni-berlin.de jwCMrXk020QagfXNZewzqgXNS9QKLPMA1SkI5b2kQihA==
Return-Path <rosuav@gmail.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; 'cpython': 0.05; 'subject:Question': 0.05; 'cc:addr:python-list': 0.09; 'literal': 0.09; 'lookup': 0.09; 'python.': 0.11; 'things.': 0.15; "(i'm": 0.16; 'from:addr:rosuav': 0.16; 'from:name:chris angelico': 0.16; 'hashes': 0.16; 'operation,': 0.16; 'reason).': 0.16; 'received:io': 0.16; 'received:psf.io': 0.16; 'wrote:': 0.16; 'looked': 0.16; 'module,': 0.18; '2015': 0.20; 'cc:2**0': 0.20; 'cc:addr:python.org': 0.20; 'assuming': 0.22; 'constant': 0.22; 'seems': 0.23; 'header:In-Reply-To:1': 0.24; 'sort': 0.25; "i've": 0.25; 'message-id:@mail.gmail.com': 0.27; 'specifically': 0.28; 'dictionary': 0.29; 'structure,': 0.29; 'common': 0.33; 'similar': 0.33; 'case,': 0.34; 'received:google.com': 0.35; 'text': 0.35; 'nov': 0.35; 'received:209.85': 0.36; 'pm,': 0.36; 'subject:: ': 0.37; 'received:209.85.213': 0.37; 'received:209': 0.38; 'names': 0.38; 'why': 0.39; 'data': 0.39; 'where': 0.40; 'still': 0.40; 'some': 0.40; 'your': 0.60; 'virtually': 0.66; 'overall': 0.72; 'chrisa': 0.84; 'stored,': 0.84; 'to:none': 0.91
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=tMHOb2Moj5fdr+Z0wvIeMmJ/Pt5UkXOnpXb9nESH0uU=; b=0Znv3giMJ2TKLQm/KWgBsuwTVUsSCM9J82tPM9Ka0P7rJRA1y6ke4BDXlf3a8q9A1k EktuB/BNDkgpKxgeHYKKPy5+FKsyHdi/A2yZkEa/IaQFCPm9CELoVkbmyDQ1cmYDWlZu pAUeOLtVTBFoAMPtvAqd/TMNi5wg4GXSIejqjYQKPaD7JUQcRYdbcQgxBN8btz2wIYpA fW6LFv7aI7gOYlC2tKJkyRJRj/ZvkqUNU2XyxEFSdIC1ejxVw/CpgsAN1If/MPA+QKxa vieF/dU4nhBKMxs0LkiyPImME1mxHOrArC62hDAXFGXrYfGlNmgf1UDyRyBbNQDQD6Nc NAtQ==
X-Received by 10.50.56.70 with SMTP id y6mr4572750igp.13.1446985681048; Sun, 08 Nov 2015 04:28:01 -0800 (PST)
In-Reply-To <n1nb0f$atn$1@dont-email.me>
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>
Xref csiph.com comp.lang.python:98447

Show key headers only | View raw

On Sun, Nov 8, 2015 at 10:19 PM, BartC <bc@freeuk.com> wrote:
> I've never understood why this seems to be necessary in Python. Why do names
> have to be looked up? (I'm assuming this is searching by name in some sort
> of table.)

Yes, if by "searching" you include hash-table lookup. A CPython
dictionary is a *highly* optimized data structure, specifically
because it's used virtually everywhere (I understand Lua's "table"
type has similar optimizations for the same reason). In the common
case, where your names come from literal text in the module, the
strings used for the lookup will be interned constants, and their
hashes will have been precalculated and stored, so the lookup is
pretty easy. So it's a constant-time operation, and while that
constant may be larger than a simple offset-and-fetch, it's still
pretty fast in the overall scheme of things.

ChrisA

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

Thread

Question about math.pi is mutable "wangq@travelsky.com" <wangq@travelsky.com> - 2015-11-06 10:33 +0800
  Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-06 12:30 +0000
    Re: Question about math.pi is mutable Lorenzo Sutton <lorenzofsutton@gmail.com> - 2015-11-06 17:12 +0100
      Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-06 19:30 +0000
        Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-07 06:40 +1100
          Re: Question about math.pi is mutable Christian Gollwitzer <auriocus@gmx.de> - 2015-11-06 20:59 +0100
          Re: Question about math.pi is mutable Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-11-06 23:19 +0100
            Re: Question about math.pi is mutable Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-11-07 00:48 +0100
            Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-07 13:00 +1100
        Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-07 14:43 +1100
          Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-07 11:23 +0000
            Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-07 22:35 +1100
              Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-07 11:57 +0000
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-07 23:15 +1100
                Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-07 13:00 +0000
                Re: Question about math.pi is mutable Laura Creighton <lac@openend.se> - 2015-11-07 15:09 +0100
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-07 16:23 +0200
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-07 16:28 +0200
                Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-07 15:01 +0000
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-07 19:46 +0200
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-08 14:07 +1100
                Re: Question about math.pi is mutable Random832 <random832@fastmail.com> - 2015-11-08 01:29 -0500
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-08 13:59 +1100
                Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-08 10:40 +0000
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 13:02 +0200
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 11:19 +0000
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 13:50 +0200
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 12:39 +0000
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 14:43 +0200
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 13:42 +0000
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 16:33 +0200
                Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 02:11 +1100
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-09 11:58 +1100
                Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-08 23:28 +1100
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-09 11:35 +1100
                Re: Question about math.pi is mutable Michael Torrie <torriem@gmail.com> - 2015-11-08 08:59 -0700
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 17:54 +0000
                Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 05:01 +1100
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 18:58 +0000
                Re: Question about math.pi is mutable Ian Kelly <ian.g.kelly@gmail.com> - 2015-11-08 12:51 -0700
                Re: Question about math.pi is mutable Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-11-08 18:13 -0500
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 23:54 +0000
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 11:00 +1100
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-09 00:11 +0000
                Re: Question about math.pi is mutable Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-11-09 08:18 -0500
                Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 11:04 +1100
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 11:26 +1100
                Re: Question about math.pi is mutable Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-11-09 21:29 +1300
                Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 11:36 +1100
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 11:50 +1100
                Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 11:56 +1100
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 12:04 +1100
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-09 22:22 +1100
                Re: Question about math.pi is mutable Random832 <random832@fastmail.com> - 2015-11-09 10:32 -0500
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-10 06:45 +1100
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-10 13:37 +1100
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-10 17:10 +1100
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-10 22:34 +1100
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-10 13:26 +0000
                Re: Question about math.pi is mutable Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-11-11 18:38 +1100
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-11 10:30 +0200
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-11 22:20 +1100
                Re: Question about math.pi is mutable Terry Reedy <tjreedy@udel.edu> - 2015-11-10 03:30 -0500
                Re: Question about math.pi is mutable Laura Creighton <lac@openend.se> - 2015-11-10 11:33 +0100
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-10 23:14 +1100
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-11 12:10 +1100
                Re: Question about math.pi is mutable Laura Creighton <lac@openend.se> - 2015-11-09 21:07 +0100
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-10 10:21 +1100
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-09 16:54 +0000
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-10 06:52 +1100
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 08:00 +1100
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 22:35 +0000
                Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 09:54 +1100
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-09 13:23 +1100
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-09 12:22 +0000
                Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 23:36 +1100
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-08 22:30 +1100
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 12:24 +0000
                Re: Question about math.pi is mutable Grant Edwards <invalid@invalid.invalid> - 2015-11-07 16:16 +0000
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-07 20:00 +0200
                Re: Question about math.pi is mutable Grant Edwards <invalid@invalid.invalid> - 2015-11-08 03:31 +0000
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 09:45 +0200
                Re: Question about math.pi is mutable Christian Gollwitzer <auriocus@gmx.de> - 2015-11-08 09:00 +0100
                Re: Question about math.pi is mutable Paul Rubin <no.email@nospam.invalid> - 2015-11-08 00:08 -0800
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 11:49 +0200
                Re: Question about math.pi is mutable Grant Edwards <invalid@invalid.invalid> - 2015-11-09 14:49 +0000
                Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-07 15:19 +0000
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-08 14:50 +1100
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 11:44 +0200
                Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-08 22:11 +1100
                Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 13:25 +0200
                Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 11:06 +0000
        Re: Question about math.pi is mutable Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-09 15:49 +0100
        Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-10 10:29 +1100
        Re: Question about math.pi is mutable Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-10 11:03 +0100
        Re: Question about math.pi is mutable Michael Torrie <torriem@gmail.com> - 2015-11-13 20:11 -0700
        Re: Question about math.pi is mutable Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-14 16:02 +0100
    Re: Question about math.pi is mutable Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-11-06 23:26 +0100
      Re: Question about math.pi is mutable Terry Reedy <tjreedy@udel.edu> - 2015-11-06 20:49 -0500
      Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-07 13:06 +1100
      Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-07 23:02 +0000
        Re: Question about math.pi is mutable Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-11-07 23:27 +0000
        Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-08 10:32 +1100
        Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-08 10:52 +1100
          Re: Question about math.pi is mutable Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-11-12 21:40 +0100
            Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-13 09:04 +1100
              Re: Question about math.pi is mutable Denis McMahon <denismfmcmahon@gmail.com> - 2015-11-13 09:19 +0000
                Re: Question about math.pi is mutable Larry Hudson <orgnut@yahoo.com> - 2015-11-13 18:30 -0800
            Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-12 22:19 +0000
              Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-13 09:52 +1100

csiph-web