Groups > comp.lang.python > #4380 > unrolled thread

What other languages use the same data model as Python?

Started by	Steven D'Aprano <steve+comp.lang.python@pearwood.info>
First post	2011-05-01 08:45 +0000
Last post	2011-05-04 07:28 -0700
Articles	20 on this page of 176 — 34 participants

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What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-01 08:45 +0000
Re: What other languages use the same data model as Python? Alec Taylor <alec.taylor6@gmail.com> - 2011-05-01 19:00 +1000
Re: What other languages use the same data model as Python? Chris Rebert <clp2@rebertia.com> - 2011-05-01 02:04 -0700
Re: What other languages use the same data model as Python? Terry Reedy <tjreedy@udel.edu> - 2011-05-01 15:10 -0400
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-02 10:37 +1200
Re: What other languages use the same data model as Python? Jorgen Grahn <grahn+nntp@snipabacken.se> - 2011-05-02 07:45 +0000
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-02 13:12 +0000
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-02 10:33 +1200
Re: What other languages use the same data model as Python? Terry Reedy <tjreedy@udel.edu> - 2011-05-01 21:42 -0400
Re: What other languages use the same data model as Python? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2011-05-02 00:28 -0700
Re: What other languages use the same data model as Python? Duncan Booth <duncan.booth@invalid.invalid> - 2011-05-02 08:43 +0000
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-03 13:39 +0100
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-03 14:49 +0000
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-03 15:20 +0000
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-03 22:10 +0100
Re: What other languages use the same data model as Python? Mel <mwilson@the-wire.com> - 2011-05-03 12:33 -0400
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-03 16:52 +0000
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-03 21:47 +0100
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-04 08:00 +1000
Re: What other languages use the same data model as Python? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-05-04 02:56 -0700
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-04 10:51 +0000
Re: What other languages use the same data model as Python? Paul Rubin <no.email@nospam.invalid> - 2011-05-04 03:58 -0700
Re: What other languages use the same data model as Python? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-05-04 06:12 -0700
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-04 14:44 +0100
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-05 00:20 +1000
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-04 18:09 +0100
Re: What other languages use the same data model as Python? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-05-04 09:18 -0700
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-04 18:03 +0100
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-05 20:55 +1200
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-05 11:31 +0100
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-07 21:21 +1200
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-07 19:28 +1000
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-08 10:39 +1200
Re: What other languages use the same data model as Python? Albert van der Horst <albert@spenarnc.xs4all.nl> - 2011-05-20 20:56 +0000
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-08 02:17 +0000
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-07 23:10 -0500
Re: What other languages use the same data model as Python? rusi <rustompmody@gmail.com> - 2011-05-07 22:48 -0700
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-09 12:52 +1200
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-09 11:38 +0100
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-09 21:18 +1000
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-09 21:53 +0100
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-09 14:29 +0000
Re: What other languages use the same data model as Python? Tim Golden <mail@timgolden.me.uk> - 2011-05-09 15:41 +0100
Re: What other languages use the same data model as Python? Ethan Furman <ethan@stoneleaf.us> - 2011-05-09 10:15 -0700
Re: What other languages use the same data model as Python? Mel <mwilson@the-wire.com> - 2011-05-09 13:38 -0400
Re: What other languages use the same data model as Python? Terry Reedy <tjreedy@udel.edu> - 2011-05-09 16:23 -0400
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-10 19:41 +1200
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-10 19:35 +1000
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-11 10:47 +1200
Re: What other languages use the same data model as Python? Terry Reedy <tjreedy@udel.edu> - 2011-05-10 15:18 -0400
Re: What other languages use the same data model as Python? Albert van der Horst <albert@spenarnc.xs4all.nl> - 2011-05-20 21:17 +0000
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-09 16:28 -0500
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-09 07:23 +0100
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-05 15:14 +0000
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-04 14:22 -0500
Re: What other languages use the same data model as Python? Benjamin Kaplan <benjamin.kaplan@case.edu> - 2011-05-04 15:46 -0400
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-04 14:58 -0500
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-04 21:40 +0100
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-05 21:31 +1200
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-05 14:50 +0000
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-05 12:14 +0000
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-05 22:37 +1000
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-04 20:58 +0100
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-04 16:49 -0500
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-05 07:12 +0100
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-05 21:08 +1200
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-05 19:12 +1000
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-05 14:30 +0000
Re: What other languages use the same data model as Python? TheSaint <nobody@nowhere.net.no> - 2011-05-07 20:18 +0800
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-05 12:49 +0000
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-05 14:31 +0000
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-05 09:40 -0500
Re: What other languages use the same data model as Python? Roy Smith <roy@panix.com> - 2011-05-05 10:49 -0400
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-04 14:47 -0500
Re: What other languages use the same data model as Python? Ben Finney <ben+python@benfinney.id.au> - 2011-05-05 07:43 +1000
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-05 12:43 +1000
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-05 15:42 +0000
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-07 22:04 +1200
Re: What other languages use the same data model as Python? Ben Finney <ben+python@benfinney.id.au> - 2011-05-08 06:09 +1000
Re: What other languages use the same data model as Python? Roy Smith <roy@panix.com> - 2011-05-07 16:24 -0400
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-08 10:54 +1200
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-08 09:43 +1000
Re: What other languages use the same data model as Python? Ben Finney <ben+python@benfinney.id.au> - 2011-05-08 11:16 +1000
Re: What other languages use the same data model as Python? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2011-05-07 23:16 -0700
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-08 16:32 +1000
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-10 13:49 +1200
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-10 03:13 +0000
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-10 14:05 +0000
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-10 16:09 +0100
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-10 15:16 +0000
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-11 01:27 +1000
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-10 16:40 +0100
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-11 01:44 +1000
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-10 13:51 +1200
Re: What other languages use the same data model as Python? MRAB <python@mrabarnett.plus.com> - 2011-05-10 03:47 +0100
Re: What other languages use the same data model as Python? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2011-05-09 23:15 -0700
Re: What other languages use the same data model as Python? John Nagle <nagle@animats.com> - 2011-05-04 14:52 -0700
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-04 19:46 -0500
Re: What other languages use the same data model as Python? John Nagle <nagle@animats.com> - 2011-05-04 21:32 -0700
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-05 22:06 +1200
Re: What other languages use the same data model as Python? John Nagle <nagle@animats.com> - 2011-05-05 08:41 -0700
Re: What other languages use the same data model as Python? Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-05 10:44 -0600
Re: What other languages use the same data model as Python? Chris Torek <nospam@torek.net> - 2011-05-06 17:57 +0000
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-07 21:39 +1200
Re: What other languages use the same data model as Python? Mel <mwilson@the-wire.com> - 2011-05-05 07:44 -0400
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-05 21:48 +1000
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-05 13:59 +0000
Re: What other languages use the same data model as Python? John Nagle <nagle@animats.com> - 2011-05-05 08:58 -0700
Re: What other languages use the same data model as Python? Neil Cerutti <neilc@norwich.edu> - 2011-05-05 13:19 +0000
Re: What other languages use the same data model as Python? Terry Reedy <tjreedy@udel.edu> - 2011-05-05 14:39 -0400
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-04 11:56 +0100
Re: What other languages use the same data model as Python? Devin Jeanpierre <jeanpierreda@gmail.com> - 2011-05-04 06:13 -0700
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-04 14:33 -0500
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-04 20:19 +0000
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-04 16:35 -0500
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-04 21:57 +0000
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-04 20:11 -0500
Re: What other languages use the same data model as Python? Mark Hammond <mhammond@skippinet.com.au> - 2011-05-05 12:09 +1000
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-04 23:01 -0500
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-05 22:19 +1200
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-05 14:17 +0000
Re: What other languages use the same data model as Python? Roy Smith <roy@panix.com> - 2011-05-05 10:31 -0400
Re: What other languages use the same data model as Python? Neil Cerutti <neilc@norwich.edu> - 2011-05-05 15:10 +0000
Re: What other languages use the same data model as Python? Roy Smith <roy@panix.com> - 2011-05-05 11:29 -0400
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-06 08:01 +1000
Re: What other languages use the same data model as Python? Neil Cerutti <neilc@norwich.edu> - 2011-05-06 13:10 +0000
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-05 16:57 +0000
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-05 16:56 +0000
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-05 11:58 -0500
Re: What other languages use the same data model as Python? Neil Cerutti <neilc@norwich.edu> - 2011-05-05 17:39 +0000
Re: What other languages use the same data model as Python? Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-05 13:13 -0600
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-05 15:12 -0500
Re: What other languages use the same data model as Python? Tim Roberts <timr@probo.com> - 2011-05-04 20:23 -0700
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-04 23:55 -0500
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-05 14:21 +0000
Re: What other languages use the same data model as Python? Mel <mwilson@the-wire.com> - 2011-05-05 08:09 -0400
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-05 07:34 +0100
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-05 14:10 +0000
Re: What other languages use the same data model as Python? Mel <mwilson@the-wire.com> - 2011-05-05 11:30 -0400
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-05 10:56 -0500
RE: What other languages use the same data model as Python? Andreas Tawn <andreas.tawn@ubisoft.com> - 2011-05-05 18:27 +0200
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-07 22:09 +1200
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-06 07:56 +1000
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-05 14:14 +0000
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-05 15:11 +0000
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-05 11:00 -0500
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-05 16:52 +0000
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-05 12:03 -0500
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-07 22:12 +1200
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-07 12:03 +0000
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-05 16:48 +0000
Re: What other languages use the same data model as Python? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2011-05-05 22:24 -0700
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-05 11:18 -0500
Re: What other languages use the same data model as Python? Ethan Furman <ethan@stoneleaf.us> - 2011-05-05 10:28 -0700
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-05 12:19 -0500
Re: What other languages use the same data model as Python? Chris Torek <nospam@torek.net> - 2011-05-06 18:17 +0000
Re: What other languages use the same data model as Python? Chris Torek <nospam@torek.net> - 2011-05-06 19:06 +0000
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-06 14:25 -0500
Re: What other languages use the same data model as Python? Chris Angelico <rosuav@gmail.com> - 2011-05-07 09:43 +1000
Re: What other languages use the same data model as Python? Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-04 16:22 -0600
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-04 19:51 -0500
Re: What other languages use the same data model as Python? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-05 14:51 +0000
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-04 21:20 +0100
Re: What other languages use the same data model as Python? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2011-05-04 22:10 -0700
Re: What other languages use the same data model as Python? harrismh777 <harrismh777@charter.net> - 2011-05-05 00:19 -0500
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-05 14:25 +0000
Re: What other languages use the same data model as Python? sturlamolden <sturla@molden.no> - 2011-05-04 07:44 -0700
Re: What other languages use the same data model as Python? Michael Torrie <torriem@gmail.com> - 2011-05-04 09:40 -0600
Re: What other languages use the same data model as Python? sturlamolden <sturla@molden.no> - 2011-05-04 09:40 -0700
Re: What other languages use the same data model as Python? Benjamin Kaplan <benjamin.kaplan@case.edu> - 2011-05-04 13:15 -0400
Re: What other languages use the same data model as Python? sturlamolden <sturla@molden.no> - 2011-05-04 10:19 -0700
Re: What other languages use the same data model as Python? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-05 15:48 +1200
Re: What other languages use the same data model as Python? Hans Georg Schaathun <hg@schaathun.net> - 2011-05-05 05:58 +0100
Re: What other languages use the same data model as Python? Grant Edwards <invalid@invalid.invalid> - 2011-05-05 14:24 +0000
Re: What other languages use the same data model as Python? Hrvoje Niksic <hniksic@xemacs.org> - 2011-05-03 15:50 +0200
Re: What other languages use the same data model as Python? sturlamolden <sturla@molden.no> - 2011-05-04 07:28 -0700

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#4606

From	Steven D'Aprano <steve+comp.lang.python@pearwood.info>
Date	2011-05-04 10:51 +0000
Message-ID	<4dc12fb4$0$29991$c3e8da3$5496439d@news.astraweb.com>
In reply to	#4605

On Wed, 04 May 2011 02:56:28 -0700, Devin Jeanpierre wrote:

> Python is pass-by-value in a
> meaningful sense, it's just that by saying that we say that the values
> being passed are references/pointers. This is maybe one level of
> abstraction below what's ideal,

"Maybe"?

Given the following statement of Python code:

>>> x = "spam"

what is the value of the variable x? Is it...?

(1) The string "spam".

(2) Some invisible, inaccessible, unknown data structure deep in the 
implementation of the Python virtual machine, which the coder cannot 
access in any way using pure Python code.

(Possibly a pointer, but since it's an implementation detail, other 
implementations may make different choices.)

(3) Something else.

I argue that any answer except for (1) is (almost always) counter-
productive: it adds more confusion than shedding light. It requires 
thinking at the wrong level, at the implementation level instead of the 
level of Python code. If we define "value" to mean the invisible, 
inaccessible reference, then that leaves no word to describe was the 
string "spam" is.

(I say "almost always" counter-productive because abstractions leak, and 
sometimes you do need to think about implementation.)

> but Scheme, Java, etc. share this
> terminology. (Ruby calls it pass-by-reference AFAIK.

The intellectual contortions that some people will go through to hammer 
the square peg of actual programming language behaviour into the two 
round holes of "pass by value" and "pass by reference" never cease to 
astonish me.

> Whatever, a rose by any other name...)

Do you really think that roses would be the symbol of romantic love if 
they were called "disgusting stink-weeds of perversion and death"?

"How was the date last night?"
"Oh, it was marvelous! He presented me with a single red stink-weed, and 
then we went to a disgusting little restaurant. I had the swill."

When people cannot agree on the definition of words, how can they 
communicate? Pass by reference Ruby is completely different from the 
older usage in Pascal, VB and other languages. Likewise, pass by value in 
Java is completely different from that in older languages. Pass by 
reference in Ruby, and pass by value in Java, describe the same thing. 
What were these people thinking?

-- 
Steven

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#4608

From	Paul Rubin <no.email@nospam.invalid>
Date	2011-05-04 03:58 -0700
Message-ID	<7x62pqn34k.fsf@ruckus.brouhaha.com>
In reply to	#4606

Steven D'Aprano <steve+comp.lang.python@pearwood.info> writes:
>>>> x = "spam"
> what is the value of the variable x? Is it...?
> (1) The string "spam".

Python works about the same way as Lisp or Scheme with regard to this
sort of thing, and those languages have been described with quite a bit
of mathematical formality.  So if you want a precise theoretical
treatment you might look at the Scheme report.  It should be pretty
clear how it carries over to Python.

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#4611

From	Devin Jeanpierre <jeanpierreda@gmail.com>
Date	2011-05-04 06:12 -0700
Message-ID	<bcb5e532-9b2f-40a5-a586-e2a7768092ad@y12g2000yqh.googlegroups.com>
In reply to	#4606

On May 4, 6:51 am, Steven D'Aprano <steve
+comp.lang.pyt...@pearwood.info> wrote:
> On Wed, 04 May 2011 02:56:28 -0700, Devin Jeanpierre wrote:
> > Python is pass-by-value in a
> > meaningful sense, it's just that by saying that we say that the values
> > being passed are references/pointers. This is maybe one level of
> > abstraction below what's ideal,
>
> "Maybe"?
>
> Given the following statement of Python code:
>
> >>> x = "spam"
>
> what is the value of the variable x? Is it...?
>
> (1) The string "spam".
>
> (2) Some invisible, inaccessible, unknowndatastructure deep in the
> implementation of the Python virtual machine, which the coder cannot
> access in any way using pure Python code.
>
> (Possibly a pointer, but since it's an implementation detail, other
> implementations may make different choices.)
>
> (3) Something else.

As I said, a pointer or reference.

> I argue that any answer except for (1) is (almost always) counter-
> productive: it adds more confusion than shedding light. It requires
> thinking at the wrong level, at the implementation level instead of the
> level of Python code. If we define "value" to mean the invisible,
> inaccessible reference, then that leaves no word to describe was the
> string "spam" is.
>
> (I say "almost always" counter-productive because abstractions leak, and
> sometimes you do need to think about implementation.)

I don't know why you want to argue that it's counter-productive when
all I said was that it was meaningful / worked.

I don't think of "pass-by-value" involving references as being an
implementation-level thing. It's a way of thinking about Python's
behavior: a model. There don't even need to be actual references or
anything resembling them inside the implementation in order to apply
the model (for example, we probably all accept that Python could be
implemented using a turing machine, which lacks references/pointers).

Also, the word you suspected did not exist is "object". So if we have
var = "spam", var is a variable containing a reference to the object
"spam". Alternatively, it's a handle for the object "spam". I think
that's the call-by-sharing terminology, anyway.

> > but Scheme, Java, etc. share this
> > terminology. (Ruby calls it pass-by-reference AFAIK.
>
> The intellectual contortions that some people will go through to hammer
> the square peg of actual programming language behaviour into the two
> round holes of "pass by value" and "pass by reference" never cease to
> astonish me.

It isn't particularly contorted. I learned Python this way and it
makes perfect sense. It's just perhaps one level of abstraction away
from the ideal of what some programmers would think in. Python's "pass-
by-value" conforms exactly to the "pass-by-value" of other languages
such as C. The only twist is that you never get to dereference
pointers in Python, but you can in C. Not much of a twist if you ask
me, but then again, I've been thinking in this model for years. Maybe
I'm brainwashed. :)

> > Whatever, a rose by any other name...)
>
> Do you really think that roses would be the symbol of romantic love if
> they were called "disgusting stink-weeds of perversion and death"?
>
> "How was the date last night?"
> "Oh, it was marvelous! He presented me with a single red stink-weed, and
> then we went to a disgusting little restaurant. I had the swill."

Please don't argue with me in this manner. The point is that words
don't matter, the meaning behind them does. As long as it's clear
what's meant, and what's meant is internally-consistent, I don't have
much problem with it. Of course, this is a rule of thumb and you could
draw extreme scenarios where it just becomes a bother.

Devin Jeanpierre

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#4613

From	Hans Georg Schaathun <hg@schaathun.net>
Date	2011-05-04 14:44 +0100
Message-ID	<7q1898-f3l.ln1@svn.schaathun.net>
In reply to	#4611

On Wed, 4 May 2011 06:12:14 -0700 (PDT), Devin Jeanpierre
  <jeanpierreda@gmail.com> wrote:
:  I don't think of "pass-by-value" involving references as being an
:  implementation-level thing. It's a way of thinking about Python's
:  behavior: a model. (...)
:  It isn't particularly contorted. I learned Python this way and it
:  makes perfect sense. It's just perhaps one level of abstraction away
:  from the ideal of what some programmers would think in. Python's "pass-
:  by-value" conforms exactly to the "pass-by-value" of other languages
:  such as C.

It is contorted and implementation-level because it is one level below
the abstraction assumed by the language.  It only works by assuming 
knowledge of C, which is language which has proved unsuitable for
complex and abstract data modelling.  Digging down into C should be 
unnecessary to explain Python.  

By calling it pass-by-value you introduce a new data type which is
unknown to Python, namely the pointer.  

:               The only twist is that you never get to dereference
:  pointers in Python, but you can in C. Not much of a twist if you ask
:  me, but then again, I've been thinking in this model for years. Maybe
:  I'm brainwashed. :)

You are.  You explain Python in terms of C.  That's useful when you 
talk to other speakers of C.

If you want to explain the language to a broader audience, you should
use terminology from the language's own level of abstraction.


-- 
:-- Hans Georg

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#4615

From	Chris Angelico <rosuav@gmail.com>
Date	2011-05-05 00:20 +1000
Message-ID	<mailman.1147.1304518838.9059.python-list@python.org>
In reply to	#4613

On Wed, May 4, 2011 at 11:44 PM, Hans Georg Schaathun <hg@schaathun.net> wrote:
> It is contorted and implementation-level because it is one level below
> the abstraction assumed by the language.  It only works by assuming
> knowledge of C, which is language which has proved unsuitable for
> complex and abstract data modelling.  Digging down into C should be
> unnecessary to explain Python.

Sometimes, to explain Python, you need to dig down to the underlying
hardware - even deeper than C, if you like. And that's always going to
be the way, because abstractions leak from time to time. Or I should
say, they occasionally have confidential briefings with the press.
Abstracting everything perfectly is neither possible nor desirable.

Chris Angelico

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#4631

From	Hans Georg Schaathun <hg@schaathun.net>
Date	2011-05-04 18:09 +0100
Message-ID	<4sd898-0el.ln1@svn.schaathun.net>
In reply to	#4615

On Thu, 5 May 2011 00:20:34 +1000, Chris Angelico
  <rosuav@gmail.com> wrote:
:  Sometimes, to explain Python, you need to dig down to the underlying
:  hardware - even deeper than C, if you like.

Sometimes you may need to narrow down the scope and explain a particular
implementation of python with its hardware, OS, and interpreter.
However, explaining just python, you do not know what the underlying
hardware/OS/interpreter is, and digging down into it is not possible.

:                                              And that's always going to
:  be the way, because abstractions leak from time to time. Or I should
:  say, they occasionally have confidential briefings with the press.
:  Abstracting everything perfectly is neither possible nor desirable.

Sure, but every language assumes a certain level of abstraction, and
when the abstraction breaks the language fails to be unambiguous and/or
portable.

-- 
:-- Hans Georg

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#4623

From	Devin Jeanpierre <jeanpierreda@gmail.com>
Date	2011-05-04 09:18 -0700
Message-ID	<b12913fb-cb13-475d-9ef7-5b6018a0f3ab@k15g2000pri.googlegroups.com>
In reply to	#4613

On May 4, 9:44 am, Hans Georg Schaathun <h...@schaathun.net> wrote:
> :               The only twist is that you never get to dereference
> :  pointers in Python, but you can in C. Not much of a twist if you ask
> :  me, but then again, I've been thinking in thismodelfor years. Maybe
> :  I'm brainwashed. :)
>
> You are.  You explain Python in terms of C.  That's useful when you
> talk to other speakers of C.
>
> If you want to explain the language to a broader audience, you should
> use terminology from the language's own level of abstraction.

No, I explained Python in terms of pointers/reference. I don't speak C
or come from a C background, I'm primarily a Python programmer. Also,
I don't agree with your notions of "should", I have seen it taught
this way to plenty of undergraduate students learning Python as their
first programming language, and they do fine. The precise notational
difference between sharing an object and copying a reference doesn't
matter, as long as you can draw a diagram of it and write/read code --
which they can, and they do fine.

I'm a bit uncomfortable with the vibe here. It's one thing for me to
self-deprecatingly suggest I'm brainwashed (with a smile), and another
for you to agree in complete seriousness.

Devin Jeanpierre

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#4629

From	Hans Georg Schaathun <hg@schaathun.net>
Date	2011-05-04 18:03 +0100
Message-ID	<9fd898-0el.ln1@svn.schaathun.net>
In reply to	#4623

On Wed, 4 May 2011 09:18:56 -0700 (PDT), Devin Jeanpierre
  <jeanpierreda@gmail.com> wrote:
:  I'm a bit uncomfortable with the vibe here. It's one thing for me to
:  self-deprecatingly suggest I'm brainwashed (with a smile), and another
:  for you to agree in complete seriousness.

I am sorry.  It was not meant to be an insult.  I do think that you
sit tightly in a frame of reference which is obviously not the only 
one appropriate, and IMNHO not the optimal one for the purpose.
"Brainwashed" was not a word I meant to take seriously.  Apologies.

I should have cut the C reference too; the same frame of reference 
could be adopted from any number of languages.  

Note that it was not the use of references as a concept I objected to,
but that they might be passed by value.  With the references being
purely abstract entities and not data objects, the idea that they
have values do not make sense.  And pass-by-value where the value
is a reference is just confusing.

-- 
:-- Hans Georg

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#4703

From	Gregory Ewing <greg.ewing@canterbury.ac.nz>
Date	2011-05-05 20:55 +1200
Message-ID	<92f70aF9pqU1@mid.individual.net>
In reply to	#4629

Hans Georg Schaathun wrote:
> With the references being
> purely abstract entities and not data objects,

It's not clear to me that references are any more abstract
than objects, or to put it another way, that objects are
any less abstract than references.

After all, in normal Python usage you never actually
*see* an object -- at best you see some string of characters
resulting from the str() or repr() of an object. The
object is a mental construct we use to make sense of the
behaviour we're seeing, as are references.

If you were to look inside the interpreter closely enough
to see the concrete representations of objects -- the
bit patterns in memory making them up -- then you would
also be able to see the bit patterns making up the
references.

-- 
Greg

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#4710

From	Hans Georg Schaathun <hg@schaathun.net>
Date	2011-05-05 11:31 +0100
Message-ID	<dtaa98-crn.ln1@svn.schaathun.net>
In reply to	#4703

On Thu, 05 May 2011 20:55:36 +1200, Gregory Ewing
  <greg.ewing@canterbury.ac.nz> wrote:
:  It's not clear to me that references are any more abstract
:  than objects, or to put it another way, that objects are
:  any less abstract than references.
: 
:  After all, in normal Python usage you never actually
:  *see* an object 

Sure, but you can refer directly to objects, pass objects around,
and refer to individual objects.  This is abstract in the sense
that it is far removed from the memory representation.  However,
the concept of a reference appears only when you explain how objects
are handled (semantics).  You cannot reference nor manipulate a 
reference in python, and that IMHO makes them more abstract.

-- 
:-- Hans Georg

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#4894

From	Gregory Ewing <greg.ewing@canterbury.ac.nz>
Date	2011-05-07 21:21 +1200
Message-ID	<92kh9cFgdcU1@mid.individual.net>
In reply to	#4710

Hans Georg Schaathun wrote:

> You cannot reference nor manipulate a 
> reference in python, and that IMHO makes them more abstract.

You can manipulate them just fine by moving them
from one place to another:

    a = b

You can use them to get at stuff they refer to:

    a = b.c
    a[:] = b[:]

You can compare them:

    if a is b:
       ...

That's about all you can do with pointers in Pascal,
and I've never heard anyone argue that Pascal pointers
are any more or less abstract than any other piece of
data in that language.

As for "referencing" a reference, you can't really do
that in Pascal either, at least not the way you can
in C, because (plain) Pascal doesn't have an address-of
operator. The only way to get a pointer to a pointer
in Pascal is to heap-allocate a single pointer, which
isn't normally a very useful thing to do.

-- 
Greg

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#4895

From	Chris Angelico <rosuav@gmail.com>
Date	2011-05-07 19:28 +1000
Message-ID	<mailman.1286.1304760534.9059.python-list@python.org>
In reply to	#4894

On Sat, May 7, 2011 at 7:21 PM, Gregory Ewing
<greg.ewing@canterbury.ac.nz> wrote:
> Hans Georg Schaathun wrote:
>
>> You cannot reference nor manipulate a reference in python, and that IMHO
>> makes them more abstract.
>
> You can manipulate them just fine by moving them
> from one place to another:

I think "manipulate" here means things like pointer arithmetic, which
are perfectly normal and common in C and assembly, but not in
languages where they're references.

Chris Angelico

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#4923

From	Gregory Ewing <greg.ewing@canterbury.ac.nz>
Date	2011-05-08 10:39 +1200
Message-ID	<92m01eFeilU1@mid.individual.net>
In reply to	#4895

Chris Angelico wrote:

> I think "manipulate" here means things like pointer arithmetic,

I don't believe that allowing arithmetic on pointers
is a prerequisite to considering them first-class values.
You can't do arithmetic on pointers in Pascal, for
example, but nobody argues that Pascal pointers are
not values.

-- 
Greg

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#5875

From	Albert van der Horst <albert@spenarnc.xs4all.nl>
Date	2011-05-20 20:56 +0000
Message-ID	<llii6g.45q@spenarnc.xs4all.nl>
In reply to	#4895

In article <mailman.1286.1304760534.9059.python-list@python.org>,
Chris Angelico  <rosuav@gmail.com> wrote:
>On Sat, May 7, 2011 at 7:21 PM, Gregory Ewing
><greg.ewing@canterbury.ac.nz> wrote:
>> Hans Georg Schaathun wrote:
>>
>>> You cannot reference nor manipulate a reference in python, and that IMHO
>>> makes them more abstract.
>>
>> You can manipulate them just fine by moving them
>> from one place to another:
>
>I think "manipulate" here means things like pointer arithmetic, which
>are perfectly normal and common in C and assembly, but not in
>languages where they're references.

Adding an integer to a reference to an array element could have been
perfectly well-defined in Algol:
        ref real operator+(ref real, int)
That is called overloading of the plus operator not "pointer arithmetic".
It is a misconception that these manipulation are dirty or ill-defined
or unsafe.

A similar extension would be possible in Python.
Allusion to assembler where one adds a number to a register
and can't tell whether the register contains an address or data
are misleading.

[This is not to say that I think it is advisable].

>
>Chris Angelico

Groetjes Albert.

--
-- 
Albert van der Horst, UTRECHT,THE NETHERLANDS
Economic growth -- being exponential -- ultimately falters.
albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst

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#4932

From	Steven D'Aprano <steve+comp.lang.python@pearwood.info>
Date	2011-05-08 02:17 +0000
Message-ID	<4dc5fd42$0$29991$c3e8da3$5496439d@news.astraweb.com>
In reply to	#4894

On Sat, 07 May 2011 21:21:45 +1200, Gregory Ewing wrote:

> Hans Georg Schaathun wrote:
> 
>> You cannot reference nor manipulate a reference in python, and that
>> IMHO makes them more abstract.
> 
> You can manipulate them just fine by moving them from one place to
> another:
> 
>     a = b

I see no reference there, nor do I see any moving taking place. What I 
see is a name binding operation. What is happening is that the name "a" 
is being bound to the object "b" (or to be precise, to whatever object is 
currently bound to name "b").

Since you haven't explained what you think is happening, I can only 
guess. My guess is that you are thinking about some implementation of the 
Python VM which uses some sort of reference internally. Perhaps it's 
CPython, which uses pointers, or some C++ implementation which actually 
uses an indirect pointer-like data structure called "reference", or maybe 
even some old-time FORTRAN I implementation that simulates pointers with 
integer indexes into a fixed size array. It could be anything.

But whatever you're thinking of, it's not the behaviour of *Python* code, 
it's behaviour of the Python virtual machine's implementation.

It astonishes me how hard it is to distinguish between abstraction levels 
when discussing computer languages. We don't have this problem in other 
fields. Nobody talking about (say) Solitaire on a computer would say:

"Blat the pixels in the rect A,B,C,D to the rect E,F,G,H. That will free 
up the Ace of Spades and allow you to memcopy the records in the far 
right column of the tableau into the foundation."

but when it comes to high-level computer languages like Python, we do the 
equivalent *all the time*. (I include myself in this.) And people get 
into (often angry) arguments over definitions, when what they're really 
arguing about is what is happening at different abstraction levels.

A simplified view:

At the Python level: binding of objects to names. No data is copied 
except by use of a direct "copy" instruction, e.g. slicing.

At the Python VM level: objects pushed and popped from a stack.

At the VM implementation level: Name binding may be implemented by 
copying pointers, or some other reference, in some data structure 
representing name spaces. Or by any other mechanism you like, so long as 
the behaviour at the Python level is the same.

At the assembly language level: memory is copied from one address to 
another.

At the hardware level: we usually describe bit manipulation in terms of 
binary AND, XOR and OR, but even that may be an abstraction: it's 
possible that the only binary op physically used by the machine is NAND.

-- 
Steven

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#4937

From	harrismh777 <harrismh777@charter.net>
Date	2011-05-07 23:10 -0500
Message-ID	<iJoxp.14507$Du7.1343@newsfe04.iad>
In reply to	#4932

Steven D'Aprano wrote:
>   Nobody talking about (say) Solitaire on a computer would say:
>
> "Blat the pixels in the rect A,B,C,D to the rect E,F,G,H. That will free
> up the Ace of Spades and allow you to memcopy the records in the far
> right column of the tableau into the foundation."
>
> but when it comes to high-level computer languages like Python, we do the
> equivalent *all the time*.

     I find exception to that argument. That is an example of the bogus 
analogy fallacy. (I am offering this in friendship, actually). The two 
cases have nothing to do with one another, do not affect one another 
directly or indirectly, and are not helpful for comparison sake. 
Analogies are generally not helpful in discussion and ought to be 
avoided generally... except for entertainment sake... and frankly I have 
found many of your analogies most entertaining (and creative) !

     Second point, we seldom do anything *all the time* /  this is a 
fallacy that presupposes extreme references, as we think about the 
argument; extreme exageration is not helpful... may or may not be 
rightly extreme, and may or may not be relevant.

     What can be said (about the argument) is that we sometimes waste 
time arguing over abstraction layers with limited cross-dependent 
understanding.

(I include myself in this.)

     (myself, as well)   ... the humility is appreciated.

> And people get
> into (often angry) arguments over definitions, when what they're really
> arguing about is what is happening at different abstraction levels.

     Sometimes. More often than not, folks are not really angry (I am 
seldom angry at my computer terminal... its one of the places where I 
relax, learn, communicate, and relate with other computer scientists who 
enjoy what they do because its enjoyable. I do agree with you that we 
all sometimes talk past each other because we're arguing from within a 
'different' level of abstraction.



kind regards,
m harris

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#4941

From	rusi <rustompmody@gmail.com>
Date	2011-05-07 22:48 -0700
Message-ID	<1cf03d24-5e64-4770-a03b-b82978b35a6b@y27g2000prb.googlegroups.com>
In reply to	#4932

On May 8, 7:17 am, Steven D'Aprano <steve
+comp.lang.pyt...@pearwood.info> wrote:
> On Sat, 07 May 2011 21:21:45 +1200, Gregory Ewing wrote:
> > Hans Georg Schaathun wrote:
>
> >> You cannot reference nor manipulate a reference in python, and that
> >> IMHO makes them more abstract.
>
> > You can manipulate them just fine by moving them from one place to
> > another:
>
> >     a = b
>
> I see no reference there, nor do I see any moving taking place. What I
> see is a name binding operation. What is happening is that the name "a"
> is being bound to the object "b" (or to be precise, to whatever object is
> currently bound to name "b").
>
> Since you haven't explained what you think is happening, I can only
> guess. My guess is that you are thinking about some implementation of the
> Python VM which uses some sort of reference internally. Perhaps it's
> CPython, which uses pointers, or some C++ implementation which actually
> uses an indirect pointer-like data structure called "reference", or maybe
> even some old-time FORTRAN I implementation that simulates pointers with
> integer indexes into a fixed size array. It could be anything.
>
> But whatever you're thinking of, it's not the behaviour of *Python* code,
> it's behaviour of the Python virtual machine's implementation.
>
> It astonishes me how hard it is to distinguish between abstraction levels
> when discussing computer languages. We don't have this problem in other
> fields. Nobody talking about (say) Solitaire on a computer would say:
>
> "Blat the pixels in the rect A,B,C,D to the rect E,F,G,H. That will free
> up the Ace of Spades and allow you to memcopy the records in the far
> right column of the tableau into the foundation."
>
> but when it comes to high-level computer languages like Python, we do the
> equivalent *all the time*.

It has to be so -- because the Turing machine like the modern computer
is an unbelievable abstraction squasher.  Yes unbelievable in the
sense that people simply cant come to terms with this.  [Witness your
"It astonishes me..." Harris: "I take exception.." etc]

The modern computer (von Neumann) <- self-modifying code <- Data=Code
<- Undecidability (Halting problem) <- Consistency XOR Completeness
(Godels theorem(s)) <- Leaky Abstractions as inevitable

If anyone thinks Godels theorems are easy trivial, he probably does
not know what he is talking about,  Yet we think that computers are
easy to understand?

[Ive personally witnessed PhDs in computer science not appreciate
compilers' inability to do certain things, and yet they could go and
take a bunch of lectures on the halting problem.  What they understand
is anybody's guess :-) ]

Coming back to topic:  The argument (about bindings, variables etc)
arises because python (like lisp) is an imperative language
masquerading as a functional one.
Such arguments dont arise in Haskell or in assembly language.
They arise and are tolerable in C.
They are terrible in C++ because all the abstractions are built to
leak.

Where python sits in this (circular) spectrum is an interesting
question
(and I watch the arguments with much interest)

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#4967

From	Gregory Ewing <greg.ewing@canterbury.ac.nz>
Date	2011-05-09 12:52 +1200
Message-ID	<92os6dF5jbU1@mid.individual.net>
In reply to	#4932

Steven D'Aprano wrote:

> Since you haven't explained what you think is happening, I can only 
> guess.

Let me save you from guessing. I'm thinking of a piece of paper with
a little box on it and the name 'a' written beside it. There is an
arrow from that box to a bigger box.

                            +-------------+
      +---+                 |             |
    a | --+---------------->|             |
      +---+                 |             |
                            +-------------+

There is another little box labelled 'b'. After executing
'a = b', both little boxes have arrows pointing to the same
big box.

                            +-------------+
      +---+                 |             |
    a | --+---------------->|             |
      +---+                 |             |
                            +-------------+
                                  ^
      +---+                       |
    b | --+-----------------------|
      +---+

In this model, a "reference" is an arrow. Manipulating references
consists of rubbing out the arrows and redrawing them differently.
Also in this model, a "variable" is a little box. It's *not* the
same thing as a name; a name is a label for a variable, not the
variable itself.

It seems that you would prefer to eliminate the little boxes and
arrows and write the names directly beside the objects:

                            +-------------+
                          a |             |
                            |             |
                          b |             |
                            +-------------+

                                 +-------------+
                               c |             |
                                 |             |
                                 |             |
                                 +-------------+

But what would you do about lists? With little boxes and arrows, you
can draw a diagram like this:

      +---+      +---+
    a | --+----->|   |      +-------------+
      +---+      +---+      |             |
                 | --+----->|             |
                 +---+      |             |
                 |   |      +-------------+
                 +---+

(Here, the list is represented as a collection of variables.
That's why variables and names are not the same thing -- the
elements of the list don't have textual names.)

But without any little boxes or arrows, you can't represent the
list itself as a coherent object. You would have to go around
and label various objects with 'a[0]', 'a[1]', etc.

                            +-------------+
                       a[0] |             |
                            |             |
                            |             |
                            +-------------+

                                 +-------------+
                            a[1] |             |
                                 |             |
                                 |             |
                                 +-------------+

This is not very satisfactory. If the binding of 'a' changes,
you have to hunt for all your a[i] labels, rub them out and
rewrite them next to different objects. It's hardly conducive
to imparting a clear understanding of what is going on,
whereas the boxes-and-arrows model makes it instantly obvious.

There is a half-way position, where we use boxes to represent
list items, but for bare names we just draw the arrow coming
directly out of the name:

                 +---+
     a --------->|   |      +-------------+
                 +---+      |             |
                 | --+----->|             |
                 +---+      |             |
                 |   |      +-------------+
                 +---+

But this is really just a minor variation. It can be a useful
shorthand, but it has the drawback of making it seem as though
the binding of a bare name is somehow different from the
binding of a list element, when it isn't really.

Finally, there's another benefit of considering a reference to
be a distinct entity in the data model. If you think of the
little boxes as being of a fixed size, just big enough to
hold a reference, then it's obvious that you can only bind it
to *one* object at a time. Otherwise it might appear that you
could draw more than one arrow coming out of a name, or write
the same name next to more than one object.

It seems to me that the boxes-and-arrows model, or something
isomorphic to it, is the most abstract model you can make of
Python that captures everything necessary to reason about it
both easily and correctly.

-- 
Greg

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#4988

From	Hans Georg Schaathun <hg@schaathun.net>
Date	2011-05-09 11:38 +0100
Message-ID	<6qsk98-em1.ln1@svn.schaathun.net>
In reply to	#4967

On Mon, 09 May 2011 12:52:27 +1200, Gregory Ewing
  <greg.ewing@canterbury.ac.nz> wrote:
:  Let me save you from guessing. I'm thinking of a piece of paper with
:  a little box on it and the name 'a' written beside it. There is an
:  arrow from that box to a bigger box.
: 
:                              +-------------+
:        +---+                 |             |
:      a | --+---------------->|             |
:        +---+                 |             |
:                              +-------------+

The flaw of this model, and I am not discounting its merits, just
pointing out that it isn't perfect, is that it creates the illusion
that references are boxes (objects) just like data objects, leading
the reader to think that we could have a reference to a reference.
If they are all boxes, by can't we make reference thereto?


-- 
:-- Hans Georg

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#4989

From	Chris Angelico <rosuav@gmail.com>
Date	2011-05-09 21:18 +1000
Message-ID	<mailman.1330.1304939912.9059.python-list@python.org>
In reply to	#4988

On Mon, May 9, 2011 at 8:38 PM, Hans Georg Schaathun <hg@schaathun.net> wrote:
> The flaw of this model, and I am not discounting its merits, just
> pointing out that it isn't perfect, is that it creates the illusion
> that references are boxes (objects) just like data objects, leading
> the reader to think that we could have a reference to a reference.
> If they are all boxes, by can't we make reference thereto?

http://www.xkcd.com/895/

Analogies are like diagrams. Not all of them are perfect or useful.

The boxes are different sizes. If you really want them to look
different, do one as squares and one as circles, but don't try that in
plain text.

Chris Angelico

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What other languages use the same data model as Python?

Contents

#4606

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#4989