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Re: The “does Python have variables?” debate

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  Re: The “does Python have variables?” debate Ned Batchelder <ned@nedbatchelder.com> - 2014-05-06 21:19 -0400
    Re: The “does Python have variables?” debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-07 09:18 +0300
      Re: The “does Python have variables?” debate Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-05-07 09:51 +0100
      Re: The “does Python have variables?” debate Ethan Furman <ethan@stoneleaf.us> - 2014-05-07 06:00 -0700
        Re: The “does Python have variables?” debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-07 17:17 +0300
          Re: The “does Python have variables?” debate Chris Angelico <rosuav@gmail.com> - 2014-05-08 00:30 +1000
      Re: The “does Python have variables?” debate Chris Angelico <rosuav@gmail.com> - 2014-05-08 00:14 +1000
        Re: The “does Python have variables?” debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-07 17:20 +0300
      Re: The “does Python have variables?” debate Jerry Hill <malaclypse2@gmail.com> - 2014-05-07 11:48 -0400
        Re: The “does Python have variables?” debate Mark H Harris <harrismh777@gmail.com> - 2014-05-07 14:31 -0500
          Re: The “does Python have variables?” debate Ben Finney <ben@benfinney.id.au> - 2014-05-08 05:57 +1000
            Re: The “does Python have variables?” debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-08 00:15 +0300
              Re: The “does Python have variables?” debate Mark H Harris <harrismh777@gmail.com> - 2014-05-07 16:35 -0500
                Re: The “does Python have variables?” debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-08 01:27 +0000
                  Re: The “does Python have variables?” debate Chris Angelico <rosuav@gmail.com> - 2014-05-08 12:09 +1000
                    Re: The “does Python have variables?” debate Steven D'Aprano <steve@pearwood.info> - 2014-05-08 03:41 +0000
                  Re: The “does Python have variables?” debate Dan Sommers <dan@tombstonezero.net> - 2014-05-08 03:43 +0000
                  Re: The “does Python have variables?” debate Mark H Harris <harrismh777@gmail.com> - 2014-05-09 17:34 -0500
                    Re: The “does Python have variables?” debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-10 01:11 +0000
                      Re: The “does Python have variables?” debate Larry Hudson <orgnut@yahoo.com> - 2014-05-10 00:46 -0700
              Re: The “does Python have variables?” debate Ben Finney <ben@benfinney.id.au> - 2014-05-08 10:35 +1000
                Re: The “does Python have variables?” debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-08 01:32 +0000
                Re: The “does Python have variables?” debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-08 09:19 +0300
                  Re: The “does Python have variables?” debate Ben Finney <ben@benfinney.id.au> - 2014-05-08 16:40 +1000
                    Re: The "does Python have variables?" debate Rustom Mody <rustompmody@gmail.com> - 2014-05-07 23:50 -0700
                      Re: The "does Python have variables?" debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-08 10:03 +0300
              Re: The “does Python have variables?” debate Ned Batchelder <ned@nedbatchelder.com> - 2014-05-07 21:33 -0400
              Re: The “does Python have variables?” debate Johannes Schneider <johannes.schneider@galileo-press.de> - 2014-05-08 09:26 +0200
                Re: The “does Python have variables?” debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-09 00:54 +0000
              Re: The “does Python have variables?” debate Joseph Martinot-Lagarde <joseph.martinot-lagarde@m4x.org> - 2014-05-08 10:07 +0200
              Re: The “does Python have variables?” debate Chris Angelico <rosuav@gmail.com> - 2014-05-08 18:14 +1000
                Re: The “does Python have variables?” debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-08 13:22 +0000
              Re: The “does Python have variables?” debate Ben Finney <ben@benfinney.id.au> - 2014-05-08 18:34 +1000
                Re: The “does Python have variables?” debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-08 12:43 +0300
                  Re: The “does Python have variables?” debate Ben Finney <ben@benfinney.id.au> - 2014-05-08 21:14 +1000
                    Re: The “does Python have variables?” debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-08 15:01 +0300
                      Re: The “does Python have variables?” debate Ben Finney <ben@benfinney.id.au> - 2014-05-09 05:14 +1000
                      Re: The “does Python have variables?” debate Ethan Furman <ethan@stoneleaf.us> - 2014-05-08 14:50 -0700
                        Re: The “does Python have variables?” debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-09 00:02 +0000
                          Re: The �  debate Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-05-09 13:10 +1200
                            Re: The �  debate Ben Finney <ben@benfinney.id.au> - 2014-05-09 13:13 +1000
                            Re: The �  debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-10 01:34 +0000
                              Re: The �  debate Mark H Harris <harrismh777@gmail.com> - 2014-05-09 21:34 -0500
                              Re: The �  debate Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-05-10 17:58 +1200
                                Re: The � debate Chris Angelico <rosuav@gmail.com> - 2014-05-10 17:10 +1000
                                  Re: The � debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-10 07:48 +0000
                                    Re: The � debate Chris Angelico <rosuav@gmail.com> - 2014-05-10 18:01 +1000
                                      Re: The � debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-10 11:21 +0300
                                    Re: The � debate Rustom Mody <rustompmody@gmail.com> - 2014-05-10 02:05 -0700
                                      Re: The � debate Ethan Furman <ethan@stoneleaf.us> - 2014-05-10 12:30 -0700
                                  Re: The � debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-10 11:18 +0300
                                    Re: The � debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-10 09:31 +0000
                  Re: The “does Python have variables?” debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-08 13:18 +0000
                    Re: The “does Python have variables?” debate Chris Angelico <rosuav@gmail.com> - 2014-05-08 23:46 +1000
                      Re: The “does Python have variables?” debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-08 14:22 +0000
                        Re: The “does Python have variables?” debate Chris Angelico <rosuav@gmail.com> - 2014-05-09 00:51 +1000
                          Re: The “does Python have variables?” debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-08 16:04 +0000
                            Re: The “does Python have variables?” debate Chris Angelico <rosuav@gmail.com> - 2014-05-09 02:10 +1000
                            Re: The “does Python have variables?” debate Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-05-08 21:02 -0400
                              Re: The “does Python have variables?” debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-09 01:32 +0000
                                Re: The “does Python have variables?” debate Roy Smith <roy@panix.com> - 2014-05-08 22:21 -0400
                                  Re: The “does Python have variables?” debate Chris Angelico <rosuav@gmail.com> - 2014-05-09 12:31 +1000
                                    Re: The "does Python have variables?" debate Rustom Mody <rustompmody@gmail.com> - 2014-05-08 22:40 -0700
                                      Re: The "does Python have variables?" debate Chris Angelico <rosuav@gmail.com> - 2014-05-09 15:51 +1000
                                        Re: The "does Python have variables?" debate Rustom Mody <rustompmody@gmail.com> - 2014-05-09 07:09 -0700
                                          Re: The "does Python have variables?" debate Chris Angelico <rosuav@gmail.com> - 2014-05-10 00:29 +1000
                                            Re: The "does Python have variables?" debate Rustom Mody <rustompmody@gmail.com> - 2014-05-09 09:07 -0700
                                  Re: The “does Python have variables?â€瑩 debate Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-05-09 19:51 -0400
                                  Re: The “does Python have variables?â€瑩 debate Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-05-10 01:03 +0100
                              Fortran (Was: The "does Python have variables?" debate) Roy Smith <roy@panix.com> - 2014-05-10 09:42 -0400
                                Re: Fortran (Was: The "does Python have variables?" debate) Terry Reedy <tjreedy@udel.edu> - 2014-05-10 14:31 -0400
                                Re: Fortran (Was: The "does Python have variables?" debate) Mark H Harris <harrismh777@gmail.com> - 2014-05-11 01:17 -0500
                                  Re: Fortran (Was: The "does Python have variables?" debate) Rustom Mody <rustompmody@gmail.com> - 2014-05-11 00:01 -0700
                                  Re: Fortran (Was: The "does Python have variables?" debate) Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-11 07:09 +0000
                                    Re: Fortran (Was: The "does Python have variables?" debate) Tomasz Rola <rtomek@ceti.pl> - 2014-05-11 18:09 +0200
                                      Re: Fortran Marko Rauhamaa <marko@pacujo.net> - 2014-05-11 19:27 +0300
                                        Re: Fortran Roy Smith <roy@panix.com> - 2014-05-11 13:51 -0400
                                          Re: Fortran Chris Angelico <rosuav@gmail.com> - 2014-05-12 04:08 +1000
                                            Re: Fortran Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-11 23:51 +0000
                                              Re: Fortran Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-05-12 01:27 +0100
                                                Re: Fortran Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-12 02:28 +0000
                                                  Re: Fortran Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-05-12 10:05 +0100
                                                  Re: Fortran Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-05-12 20:52 -0400
                                          Re: Fortran Ethan Furman <ethan@stoneleaf.us> - 2014-05-11 11:05 -0700
                                          Re: Fortran Chris Angelico <rosuav@gmail.com> - 2014-05-12 04:33 +1000
                                            Re: Fortran Roy Smith <roy@panix.com> - 2014-05-11 14:43 -0400
                                              Re: Fortran Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-11 23:15 +0000
                                                Re: Fortran MRAB <python@mrabarnett.plus.com> - 2014-05-12 00:51 +0100
                                                  Re: Fortran Roy Smith <roy@panix.com> - 2014-05-11 20:14 -0400
                                                    Re: Fortran alister <alister.nospam.ware@ntlworld.com> - 2014-05-12 14:14 +0000
                                                  Re: Fortran Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-12 01:11 +0000
                                                    Re: Fortran Dave Angel <d@davea.name> - 2014-05-11 23:27 -0400
                                                    Re: Fortran Grant Edwards <invalid@invalid.invalid> - 2014-05-12 14:07 +0000
                                              Re: Fortran Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-05-11 21:12 -0400
                                    Re: Fortran (Was: The "does Python have variables?" debate) Chris Angelico <rosuav@gmail.com> - 2014-05-12 02:42 +1000
                                    Re: Fortran Tomasz Rola <rtomek@ceti.pl> - 2014-05-11 20:04 +0200
                                    Re: Fortran Chris Angelico <rosuav@gmail.com> - 2014-05-12 04:12 +1000
                                  Re: Fortran (Was: The "does Python have variables?" debate) Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2014-05-11 19:05 +0200
                                    Re: Fortran (Was: The "does Python have variables?" debate) Mark H Harris <harrismh777@gmail.com> - 2014-05-11 13:54 -0500
                                      Re: Fortran (Was: The "does Python have variables?" debate) Chris Angelico <rosuav@gmail.com> - 2014-05-12 04:59 +1000
                                        Re: Fortran (Was: The "does Python have variables?" debate) Mark H Harris <harrismh777@gmail.com> - 2014-05-11 14:14 -0500
                                          Re: Fortran (Was: The "does Python have variables?" debate) albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-05-29 14:06 +0000
                                            Re: Fortran (Was: The "does Python have variables?" debate) Peter Pearson <ppearson@nowhere.invalid> - 2014-05-29 17:53 +0000
                                      Re: Fortran (Was: The "does Python have variables?" debate) Dave Angel <davea@davea.name> - 2014-05-11 23:10 -0400
                                        Re: Fortran (Was: The "does Python have variables?" debate) Mark H Harris <harrismh777@gmail.com> - 2014-05-11 23:10 -0500
                                          Re: Fortran (Was: The "does Python have variables?" debate) Mark H Harris <harrismh777@gmail.com> - 2014-05-11 23:26 -0500
                                            Re: Fortran (Was: The "does Python have variables?" debate) Chris Angelico <rosuav@gmail.com> - 2014-05-12 14:53 +1000
                                      Re: Fortran (Was: The "does Python have variables?" debate) Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2014-05-12 10:44 +0200
                                        Re: Fortran (Was: The "does Python have variables?" debate) Mark H Harris <harrismh777@gmail.com> - 2014-05-13 00:33 -0500
                                          Re: Fortran (Was: The "does Python have variables?" debate) Steven D'Aprano <steve@pearwood.info> - 2014-05-13 05:48 +0000
                                            Re: Fortran (Was: The "does Python have variables?" debate) Mark H Harris <harrismh777@gmail.com> - 2014-05-13 00:55 -0500
                                            Re: Fortran (Was: The "does Python have variables?" debate) Chris Angelico <rosuav@gmail.com> - 2014-05-13 15:56 +1000
                                              Re: Fortran (Was: The "does Python have variables?" debate) Steven D'Aprano <steve@pearwood.info> - 2014-05-13 09:34 +0000
                                                Re: Fortran (Was: The "does Python have variables?" debate) Chris Angelico <rosuav@gmail.com> - 2014-05-13 20:00 +1000
                                                  Re: Fortran (Was: The "does Python have variables?" debate) Rustom Mody <rustompmody@gmail.com> - 2014-05-13 03:44 -0700
                                                    Re: Fortran (Was: The "does Python have variables?" debate) Chris Angelico <rosuav@gmail.com> - 2014-05-13 20:50 +1000
                                            Re: Fortran (Was: The "does Python have variables?" debate) Gene Heskett <gheskett@wdtv.com> - 2014-05-13 02:31 -0400
                                              Re: Fortran (Was: The "does Python have variables?" debate) Steven D'Aprano <steve@pearwood.info> - 2014-05-13 07:22 +0000
                                                Re: Fortran (Was: The "does Python have variables?" debate) Roy Smith <roy@panix.com> - 2014-05-13 07:16 -0400
                                                  Re: Fortran (Was: The "does Python have variables?" debate) Chris Angelico <rosuav@gmail.com> - 2014-05-13 21:21 +1000
                                                  Re: Fortran (Was: The "does Python have variables?" debate) Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-05-13 14:42 +0100
                                                Re: Fortran (Was: The "does Python have variables?" debate) Gene Heskett <gheskett@wdtv.com> - 2014-05-13 07:42 -0400
                                          Re: Fortran Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2014-05-13 19:33 +0200
                                            Re: Fortran Marko Rauhamaa <marko@pacujo.net> - 2014-05-13 22:57 +0300
                                              Re: Fortran Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-14 00:10 +0000
                                                Re: Fortran Ian Kelly <ian.g.kelly@gmail.com> - 2014-05-13 21:43 -0600
                                                Re: Fortran Marko Rauhamaa <marko@pacujo.net> - 2014-05-14 07:35 +0300
                                                  Re: Fortran Steven D'Aprano <steve@pearwood.info> - 2014-05-14 06:58 +0000
                                                    Re: Fortran Marko Rauhamaa <marko@pacujo.net> - 2014-05-14 11:46 +0300
                                                Re: Fortran Sturla Molden <sturla.molden@gmail.com> - 2014-05-14 23:05 +0000
                                                struct.unpack: why 's' fmt char convert to bytestring GuoChao <cx63@outlook.com> - 2014-05-15 20:34 +0800
                                                Re: struct.unpack: why 's' fmt char convert to bytestring Dave Angel <davea@davea.name> - 2014-05-15 09:49 -0400
                                                Re: struct.unpack: why 's' fmt char convert to bytestring MRAB <python@mrabarnett.plus.com> - 2014-05-15 15:47 +0100
                                              Re: Fortran Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2014-05-14 15:13 +0200
                                              Re: Fortran albert@spenarnc.xs4all.nl (Albert van der Horst) - 2014-05-29 14:26 +0000
                                                Re: Fortran Marko Rauhamaa <marko@pacujo.net> - 2014-05-29 17:50 +0300
                                                  Re: Fortran Chris Angelico <rosuav@gmail.com> - 2014-05-30 00:58 +1000
                                                    Re: Fortran Marko Rauhamaa <marko@pacujo.net> - 2014-05-29 18:09 +0300
                                                  Re: Fortran Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-29 17:57 +0000
                                                    Re: Fortran Marko Rauhamaa <marko@pacujo.net> - 2014-05-29 21:55 +0300
                            Re: The “does Python have variables?” debate Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-05-09 09:13 +0100
                    Re: The “does Python have variables?” debate Michael Torrie <torriem@gmail.com> - 2014-05-08 08:06 -0600
                    Re: The “does Python have variables?” debate Chris Angelico <rosuav@gmail.com> - 2014-05-09 00:13 +1000
              Re: The “does Python have variables?” debate Terry Reedy <tjreedy@udel.edu> - 2014-05-08 15:21 -0400
                Re: The “does Python have variables?” debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-08 23:06 +0300
                  Re: The “does Python have variables?” debate Ethan Furman <ethan@stoneleaf.us> - 2014-05-08 15:36 -0700
              Re: The “does Python have variables?” debate Ethan Furman <ethan@stoneleaf.us> - 2014-05-08 17:05 -0700
              Re: The “does Python have variables?” debate Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-05-09 01:47 +0100
        Re: The “does Python have variables?” debate Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-05-08 00:57 +0000
        Re: The “does Python have variables?” debate Roy Smith <roy@panix.com> - 2014-05-08 08:41 -0400
          Re: The “does Python have variables?” debate Chris Angelico <rosuav@gmail.com> - 2014-05-08 22:54 +1000
          Re: The “does Python have variables?” debate Ethan Furman <ethan@stoneleaf.us> - 2014-05-08 06:18 -0700
            Re: The “does Python have variables?” debate Marko Rauhamaa <marko@pacujo.net> - 2014-05-08 17:03 +0300
              Re: The “does Python have variables?” debate Ethan Furman <ethan@stoneleaf.us> - 2014-05-08 16:09 -0700
          Re: The “does Python have variables?” debate "Neil D. Cerutti" <neilc@norwich.edu> - 2014-05-08 10:47 -0400

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#71156

On 09/05/2014 02:02, Dennis Lee Bieber wrote:
> On 08 May 2014 16:04:51 GMT, Steven D'Aprano
> <steve+comp.lang.python@pearwood.info> declaimed the following:
>
>> Personally, I think that trying to be general and talk about "many other
>> languages" is a failing strategy. Better to be concrete: C, Pascal,
>> Algol, Fortran, VB (I think) are good examples of the "value in a box at
>> a fixed location" model. Of those, Algol, Pascal and Fortran are either
>> obsolete or legacy, and C is by far the most well-known by people here.
>> (For some reason, few people seem to migrate from VB to Python.) Hence,
>> "C-like".
>>
>
> 	Obsolete and Legacy? Fortran still receives regular standards updates
> (currently 2008, with the next revision due in 2015).
>

http://arstechnica.com/science/2014/05/scientific-computings-future-can-any-coding-language-top-a-1950s-behemoth/

-- 
My fellow Pythonistas, ask not what our language can do for you, ask 
what you can do for our language.

Mark Lawrence

---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

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#71103

On 05/08/2014 07:18 AM, Steven D'Aprano wrote:
> Nobody has suggested flogging anyone, not even figuratively. Unless you 
> believe that correcting a misapprehension, no matter how gently it is 
> done, is a flogging, I don't see how you draw the conclusion that Ben is 
> talking about flogging anyone.

Agreed, although this entire thread of conversation kind of illustrates
a kind of debating of issues that happen regularly on this mailing list
and probably does turn off a lot of newbies, and probably turned off the
original poster a long time ago.

Kind of reminds me of the three-headed knight scene in Monty Python.
While the heads debate amongst themselves, Robin sneaks off and the
heads don't even notice.  Here, someone comes along and asks the list a
question, and while answering the question, the discussion rapidly takes
off in its own direction as members debate some underlying fact that may
or may not be important to the original poster.  In fact by now I'm sure
most people have completely forgotten the original post entirely and I'm
can't even remember if we even answered his question.  But I am pretty
sure he's long gone from the lists.  Of course there is also a problem
of drive-by questions on this list, so we often never know if the poster
did get an answer.

Obviously there's nothing wrong with having this discussion in general.
 I think it's been quite interesting.

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#71104

On Fri, May 9, 2014 at 12:06 AM, Michael Torrie <torriem@gmail.com> wrote:
> Agreed, although this entire thread of conversation kind of illustrates
> a kind of debating of issues that happen regularly on this mailing list
> and probably does turn off a lot of newbies, and probably turned off the
> original poster a long time ago.

The subject line has been changed. I don't see a problem with
tangential discussions that were spawned by someone's question.

ChrisA

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#71122

On 5/8/2014 4:14 AM, Chris Angelico wrote:
> On Thu, May 8, 2014 at 6:07 PM, Joseph Martinot-Lagarde
> <joseph.martinot-lagarde@m4x.org> wrote:
>> For me, names bound to values is the same concept as pointer pointing to
>> memory.

You are missing a level of indirection. In CPython, a name (always in 
some namespace) represents a pointer to a pointer. The first pointer is 
calculated as an offset from the base pointer of the namespace. For a C 
array namespace (used for functions), the offset is constant (for that 
function and namespace). For a python dict namespace, the offset is 
calculated from the hash of the name, the size of the dict, and the 
previous contents of the hash table. This complication allows the 
namespace to grow and shrink. In either case, the second pointer if 
overwritten to 'rebind' the name.

>> bar = foo copies the pointer and not the underlying memory.

It copies the second pointer of foo, in the underlying memory pointed at 
by the foo's first pointer, to the memory pointed at by bar's first pointer.

 >> This is not a foreign concept to C programmers.

Once one gets the indirection correct.

> That is how it's implemented in CPython, after all... modulo the whole
> refcounting thing, of course. But that's not strictly a part of the
> definition of Python; it's just implementation. You could implement
> Python on pencil-and-paper (aka a dry run), and as long as you have a
> concept of names that reference objects, it's going to be fine.

For paper-aided mental execution, most people would not bother to 
implement version and run dependent features, such as 'id()' and most of 
the possible uses of 'is' (other than 'is None', etc.). For code that 
also avoids such features, such shortcuts would indeed be fine.

> "reference" might be done with a physical piece of string connecting a
> Post-It note with a name to a box with the object's state, meaning
> there's no way of copying any pointer, and it's still Python.

-- 
Terry Jan Reedy

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#71127

Terry Reedy <tjreedy@udel.edu>:

>> On Thu, May 8, 2014 at 6:07 PM, Joseph Martinot-Lagarde
>> <joseph.martinot-lagarde@m4x.org> wrote:
>>> For me, names bound to values is the same concept as pointer
>>> pointing to memory.
>
> You are missing a level of indirection. In CPython, a name (always in
> some namespace) represents a pointer to a pointer. The first pointer
> is calculated as an offset from the base pointer of the namespace. For
> a C array namespace (used for functions), the offset is constant (for
> that function and namespace). For a python dict namespace, the offset
> is calculated from the hash of the name, the size of the dict, and the
> previous contents of the hash table. This complication allows the
> namespace to grow and shrink. In either case, the second pointer if
> overwritten to 'rebind' the name.

Terry, you are talking about an implementation. Joseph is talking about
the concept.

You can tell a C programmer that a Python variable always holds a
pointer to an object, and they get the idea right away ("Oh, so '.' in
Python is the same as '->' in C") and start producing efficient, correct
Python code.


Marko

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#71134

On 05/08/2014 01:06 PM, Marko Rauhamaa wrote:
> Terry Reedy <tjreedy@udel.edu>:
>
>>> On Thu, May 8, 2014 at 6:07 PM, Joseph Martinot-Lagarde
>>> <joseph.martinot-lagarde@m4x.org> wrote:
>>>> For me, names bound to values is the same concept as pointer
>>>> pointing to memory.
>>
>> You are missing a level of indirection. In CPython, a name (always in
>> some namespace) represents a pointer to a pointer. The first pointer
>> is calculated as an offset from the base pointer of the namespace. For
>> a C array namespace (used for functions), the offset is constant (for
>> that function and namespace). For a python dict namespace, the offset
>> is calculated from the hash of the name, the size of the dict, and the
>> previous contents of the hash table. This complication allows the
>> namespace to grow and shrink. In either case, the second pointer if
>> overwritten to 'rebind' the name.
>
> Terry, you are talking about an implementation. Joseph is talking about
> the concept.
>
> You can tell a C programmer that a Python variable always holds a
> pointer to an object, and they get the idea right away ("Oh, so '.' in
> Python is the same as '->' in C") and start producing efficient, correct
> Python code.

Right up until they want to dereference.

--
~Ethan~

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#71138

Back when I was trying to learn the differences between Python's name-binding and C-like variables, a couple folks 
stepped up and provided great assistance.

This first email, while delving into details that are not accessible in Python, still helped a great deal:

https://mail.python.org/pipermail/python-list/2009-February/526880.html


This next explained why the previous, while accurate from a CS standpoint, was not useful in Python as Python simply 
does not allow access to one of the layers, so trying to think about that layer when working with Python is not productive:

https://mail.python.org/pipermail/python-list/2009-February/526909.html

--
~Ethan~

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#71139

On 09/05/2014 01:05, Ethan Furman wrote:
> Back when I was trying to learn the differences between Python's
> name-binding and C-like variables, a couple folks stepped up and
> provided great assistance.
>
> This first email, while delving into details that are not accessible in
> Python, still helped a great deal:
>
> https://mail.python.org/pipermail/python-list/2009-February/526880.html
>
>
> This next explained why the previous, while accurate from a CS
> standpoint, was not useful in Python as Python simply does not allow
> access to one of the layers, so trying to think about that layer when
> working with Python is not productive:
>
> https://mail.python.org/pipermail/python-list/2009-February/526909.html
>
> --
> ~Ethan~

Please, please can the link directly above be regarded as the final, 
final say on this matter?  Thank you in anticipation.

-- 
My fellow Pythonistas, ask not what our language can do for you, ask 
what you can do for our language.

Mark Lawrence

---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com

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#71063

On Wed, 07 May 2014 11:48:15 -0400, Jerry Hill wrote:

> On Wed, May 7, 2014 at 2:18 AM, Marko Rauhamaa <marko@pacujo.net> wrote:
>> Ned Batchelder <ned@nedbatchelder.com>:
>>
>>> Why is "variable" sacrosanct and can only be used to describe C
>>> semantics, but we're OK reusing class, int, and function?
>>
>> The Python language specification calls them variables; the terminology
>> discussion should end there.
> 
> Personally, I found the idea that a python variable is a name + value
> pairing to be useful when learning the language, especially when I was
> struggling with the calling semantics (that is, the differences between
> call-by-value, call-by-reference, and call-by-object).  I think it's
> rather silly for someone to insist that python doesn't have variables. 
> On the other hand, I think it can be useful to point out that python
> variable aren't like C variables, and that thinking of python variables
> as having two parts -- names and values -- really can help people who
> are struggling to learn the language.  I know it certainly helped me.

+1

I was in the same position, and I found that while I saw people talking 
about "name bindings" and similar, the difference never sank in until 
somebody (I forget who) said "Python doesn't have variables, it has name 
bindings". Until then, I was still labouring under the misapprehension 
that my mental model of variables I learned from Pascal (equivalent to 
that of C) applied to Python too. Being exposed to an outrageous claim 
like "Python has no variables" lead me to question my assumptions.

Most of the time, when you're just assigning values to a variable name, 
it's a difference that makes no difference. But at the edges, you run 
into some of the differences:

* If you think that variables are necessarily known at compile-time, 
  then Python has no variables.

* If you think that variables have an address, then Python has no 
  variables.

* If you think of variables as a box inside of which the compiler 
  puts a value, then Python has no variables.

* If you think of id(x) as the identity of the *name* "x" rather
  than the identity of the object bound to "x", that is, if you
  think of id(x) as like a pointer to x, then you are mistaken.




-- 
Steven D'Aprano
http://import-that.dreamwidth.org/

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#71093

In article <mailman.9742.1399477705.18130.python-list@python.org>,
 Jerry Hill <malaclypse2@gmail.com> wrote:

> thinking of python variables as having two parts -- names and values 
> -- really can help people who are struggling to learn the language.

There's many levels of learning, and we see them all on this list.

For people who are just learning programming, and are learning Python as 
their first language, we need to keep things simple.  These are the 
people who are still struggling to understand basic concepts such as 
algorithms, loops, and the most fundamental data structures.  For those 
people, talking about variables as a container to hold a value is the 
right level of abstraction.

At some point, that model no longer fits reality well enough that it 
becomes a barrier to further learning.  When I write:

def mutate(x, y):
    x = 42
    y[0] = 42

x = 4
y = [4]

mutate(x, y)
print x, y

and run it, unless I really understand about name binding and argument 
passing, I'm going to be totally befuddled by the result.  At that 
point, I need to unlearn something I thought I understood, and that's 
really hard (en.wikipedia.org/wiki/Principles_of_learning#Primacy).

So, this leads us to the classic dilemma in teaching.  If I simplify 
things at first, it's easier to learn initially, but I'm setting the 
student up for problems later.  If I try to be 100% correct about 
everything initially, it's like drinking from a firehose.  It's hard to 
say which is better.  I do know that when I first learned F = M * A in 
high-school physics, we didn't worry about what happens if the M is 
moving very fast, or is very small, or if its quarks are spinning in the 
wrong direction.

OK, so that takes care of newbies.  There's another whole class of 
people who learn Python.  These are the people who have been doing this 
for a long time.  They already know several of C, C++, Java, Lisp, 
Javascript, Go, Fortran, Pascal, Forth, etc.  For them, learning a new 
language is an entirely different process from the newbie.  For them, 
it's just a matter of "Oh, yeah, Python does classes this way, and has 
that kind of scoping, and the standard library includes this bunch of 
data structures, and ints are really bignums, and this flavor of 
strings, and there's some funky whitespace thing going on".  Those are 
the people who want to know about name binding up front.

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#71094

On Thu, May 8, 2014 at 10:41 PM, Roy Smith <roy@panix.com> wrote:
> At some point, that model no longer fits reality well enough that it
> becomes a barrier to further learning.  When I write:
>
> def mutate(x, y):
>     x = 42
>     y[0] = 42
>
> x = 4
> y = [4]
>
> mutate(x, y)
> print x, y
>
> and run it, unless I really understand about name binding and argument
> passing, I'm going to be totally befuddled by the result.

Easiest way to explain that is probably to just say, right at the
beginning, that *assignment to a name is special*. When you assign to
x inside mutate(), stuff happens. You're not assigning to y, so
different stuff happens. If you called a method on y, or anything like
that, it'd be the same kind of "stuff" as you're seeing here; but
assigning directly to the name is a different sort of operation from
everything else. (Explaining the difference between "x = x + 1" and "x
+= 1" can come later. MUCH later, probably when you try to augassign
to a tuple's element.)

The advantage of singling out assignment is that, as well as handling
the difference between rebinding and mutation, it also picks up the
magic "this is now local" mode change. Compare:

x = [1,2,3]
def mutate1():
    x += [4]
def mutate2():
    x.append(4)

One of them needs a 'global' declaration to work, and the other
doesn't, because assigning is special.

ChrisA

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#71099

On 05/08/2014 05:41 AM, Roy Smith wrote:
> In article <mailman.9742.1399477705.18130.python-list@python.org>,
>   Jerry Hill <malaclypse2@gmail.com> wrote:
>
>> thinking of python variables as having two parts -- names and values
>> -- really can help people who are struggling to learn the language.
>
> There's many levels of learning, and we see them all on this list.
>
> For people who are just learning programming, and are learning Python as
> their first language, we need to keep things simple.  These are the
> people who are still struggling to understand basic concepts such as
> algorithms, loops, and the most fundamental data structures.  For those
> people, talking about variables as a container to hold a value is the
> right level of abstraction.

-1

There is nothing wrong with simplifying concepts for newbies, but use one that fits the language.  There is nothing 
difficult with either the sticky note analogy or the pieces of paper and a string analogy.

Teaching someone that Python variables are containers is a massive fail.


> OK, so that takes care of newbies.  There's another whole class of
> people who learn Python.  These are the people who have been doing this
> for a long time.

There's also the whole class of programmers who only know one language, or only a small handful of related languages 
that all pretty much operate the same as far as variables are concerned.  The simple analogies is also helpful for them.

--
~Ethan~

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#71102

Ethan Furman <ethan@stoneleaf.us>:

> On 05/08/2014 05:41 AM, Roy Smith wrote:
>> For those people, talking about variables as a container to hold a
>> value is the right level of abstraction.
>
> [...]
>
> Teaching someone that Python variables are containers is a massive fail.

But that's what they are.

We are really debating on the suitability of a metaphor. The palm of my
hand is a "container" for a horse. You can ask, Which horse are you
holding? when it's only the reins I'm holding.

Or maybe we can think of Python's data model as a city with structures
of different sizes and shapes. A variable is a container that holds the
address of a structure...


Marko

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#71135

On 05/08/2014 07:03 AM, Marko Rauhamaa wrote:
> Ethan Furman <ethan@stoneleaf.us>:
>> On 05/08/2014 05:41 AM, Roy Smith wrote:
>>>
>>> For those people, talking about variables as a container to hold a
>>> value is the right level of abstraction.
>>
>> Teaching someone that Python variables are containers is a massive fail.
>
> But that's what they are.

No, it's not.


> We are really debating on the suitability of a metaphor.

Exactly.  And the "a variable is a box that holds the value" is a great metaphor for languages that assign a name to a 
fixed location -- languages such as Pascal, Basic, FoxPro, and C.  In these languages when you say `a = b` you now have 
*two* copies of the data (at least for the most part); in Python (and similar languages) you have two *names* for one 
copy of the data.


> Or maybe we can think of Python's data model as a city with structures
> of different sizes and shapes. A variable is a container that holds the
> address of a structure...

If that helps as a stepping stone to a true model, fine; but if that's the final destination of your understanding then 
you don't truly understand Python's data model.

--
~Ethan~

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#71107

On 5/8/2014 8:41 AM, Roy Smith wrote:
> In article <mailman.9742.1399477705.18130.python-list@python.org>,
>   Jerry Hill <malaclypse2@gmail.com> wrote:
>
>> thinking of python variables as having two parts -- names and values
>> -- really can help people who are struggling to learn the language.
>
> There's many levels of learning, and we see them all on this list.
>
> For people who are just learning programming, and are learning Python as
> their first language, we need to keep things simple.  These are the
> people who are still struggling to understand basic concepts such as
> algorithms, loops, and the most fundamental data structures.  For those
> people, talking about variables as a container to hold a value is the
> right level of abstraction.
>
> At some point, that model no longer fits reality well enough that it
> becomes a barrier to further learning.  When I write:
>
> def mutate(x, y):
>      x = 42
>      y[0] = 42
>
> x = 4
> y = [4]
>
> mutate(x, y)
> print x, y
>
> and run it, unless I really understand about name binding and argument
> passing, I'm going to be totally befuddled by the result.  At that
> point, I need to unlearn something I thought I understood, and that's
> really hard (en.wikipedia.org/wiki/Principles_of_learning#Primacy).

The "surprising" things can be demonstrated without using functions. 
Once assignment statements are mastered, the way argument passing works 
can be extrapolated. New programmers will have to further be taught 
about shadowing and scopes, while experienced programmers should already 
be up and running (until they try to get cute).

Of course everybody has to eventually learn about the special syntax 
usable in function definitions and function calls.

-- 
Neil Cerutti

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