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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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#71001 — Re: The “does Python have variables?” debate

On 5/6/14 7:55 PM, Ben Finney wrote:
> Ned Batchelder <ned@nedbatchelder.com> writes:
>
>> This meme bugs me so much. Python has variables. They work differently
>> than variables in C.
>
> Which is why it's useful to intervene right at the start when someone
> comes in with assumptions about “variables”; it's better that they
> discard that baggage and learn about reference binding, instead.

Where do you draw the line?  Python ints work differently than C ints, 
but we don't seem to mind using the same word for them. Same for strings 
and functions.  Python's classes work differently than C++ or Java's, 
but we don't say that Python has no classes.

And let's not discuss Lisp's lists, Haskell's functions, or Modula-2's 
modules.

So many terms are used and re-used, and each language has differences. 
Why is "variable" sacrosanct and can only be used to describe C 
semantics, but we're OK reusing class, int, and function?

>
>> In fact, they work by having names bound to values.
>
> My position is that this concept is sufficiently different to what most
> newcomers to Python mean by “variable” (those who have the term at all;
> and for those who don't, no need to introduce potentially-confusing
> terms) that it's better to avoid that term entirely and immediately use
> more-accurate terminology.
>
>> If you want to insist that Python has no variables, you will have to
>> also say that neither do Javascript, Ruby, Java, PHP, etc.
>
> I don't know enough Ruby to comment there. For Java, Javascript, PHP,
> they *do* have variables that work pretty much as expected by these
> newcomers: the variables are declared and exist before a value is
> assigned, they have the “box containing a value” conceptual model (as
> contrasted with Python's “value with sticky-notes attached” model), the
> “how do I pass by reference or by value?” question is meaningful — all
> of these are significantly different in Python, so the term “variable”
> is useful in those other languages but mostly just a confusing obstacle
> in learning Python.

As Chris A. has pointed out, Javascript works like Python, and not much 
like C.

>
>> And if Javascript has no variables, what does the var keyword mean?
>
> Exactly; JavaScript *does* have variables, in the ways Python does not.
>


-- 
Ned Batchelder, http://nedbatchelder.com

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#71007

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.

The complaint against variables seems to hinge on the fact that Python
variables are not first-class objects. A manifestation of that is that
you can't pass variables by reference to functions.

Actually, while Python variables are not first-class objects, one could
see them as dictionary-key pairs. So you can even pass them by reference
by passing the dictionary and the key.

Then the problem is lists. You can't represent a list element as a
dictionary-key pair. Or can you? A list can be viewed as a "dictionary"
whose key is an integer. Thus, the same pass-by-reference technique
would work for lists as well.


Marko

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#71012

On 07/05/2014 07:18, Marko Rauhamaa 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.
>

I entirely agree.  This discussion has been done to death an infinite 
number of times.  It fits into my "I couldn't care less" category, I 
just want to write code.

-- 
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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#71019

On 05/06/2014 11:18 PM, Marko Rauhamaa wrote:
>
> Actually, while Python variables are not first-class objects, one could
> see them as dictionary-key pairs. So you can even pass them by reference
> by passing the dictionary and the key.

Well, you could pass them that way, but not necessarily change them:

--> def func1():
...   a = 1
...   b = 2
...   swap(locals(), 'a', 'b')
...   print a
...   print b
...
--> def swap(d, key1, key2):
...   print d[key1], d[key2]
...   d[key1], d[key2] = d[key2], d[key1]
...   print d[key1], d[key2]
...
--> func1()
1 2
2 1
1
2

--
~Ethan~

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#71022

Ethan Furman <ethan@stoneleaf.us>:

> On 05/06/2014 11:18 PM, Marko Rauhamaa wrote:
>> Actually, while Python variables are not first-class objects, one
>> could see them as dictionary-key pairs. So you can even pass them by
>> reference by passing the dictionary and the key.
>
> Well, you could pass them that way, but not necessarily change them:

Weird. Some other tests of mine did work. But:

   Note: The contents of this dictionary should not be modified; changes
   may not affect the values of local and free variables used by the
   interpreter. [<URL:
   https://docs.python.org/2/library/functions.html#locals>]


Marko

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#71024

On Thu, May 8, 2014 at 12:17 AM, Marko Rauhamaa <marko@pacujo.net> wrote:
> Weird. Some other tests of mine did work. But:
>
>    Note: The contents of this dictionary should not be modified; changes
>    may not affect the values of local and free variables used by the
>    interpreter. [<URL:
>    https://docs.python.org/2/library/functions.html#locals>]

If you test locals() at module level (including the interactive
interpreter), things will work, because it just returns the same dict
as globals() returns. It's only inside an actual function that it's
different and magical.

ChrisA

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#71021

On Wed, May 7, 2014 at 11:00 PM, Ethan Furman <ethan@stoneleaf.us> wrote:
> On 05/06/2014 11:18 PM, Marko Rauhamaa wrote:
>>
>> Actually, while Python variables are not first-class objects, one could
>> see them as dictionary-key pairs. So you can even pass them by reference
>> by passing the dictionary and the key.
>
>
> Well, you could pass them that way, but not necessarily change them:
> [ chomp demo code using locals() ]

That's because, while you can *think of* Python name bindings as being
like dict key/value pairs, they aren't always that. Function locals,
class locals, and other such namespaces aren't necessarily implemented
with dicts. They're conceptually still a "dictionary" of sorts, but
you can't actually pass anyone a dict and key and expect it to work.

ChrisA

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#71023

Chris Angelico <rosuav@gmail.com>:

> That's because, while you can *think of* Python name bindings as being
> like dict key/value pairs, they aren't always that. Function locals,
> class locals, and other such namespaces aren't necessarily implemented
> with dicts. They're conceptually still a "dictionary" of sorts, but
> you can't actually pass anyone a dict and key and expect it to work.

I see that as a glitch in the Matrix.


Marko

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#71036

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.

-- 
Jerry

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#71048

On 5/7/14 10:48 AM, Jerry Hill wrote:
> 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.
>

But here is the rub:  BASIC also has -- names and values --;  although 
they are in a variable table, and they refer to memory not objects.

C is the same, basically.  ehem.  ... a name bound to an address that 
references a chunk of memory (by type) of a certain length.

... and we could go on.

But, Python's names bound to objects not only doesn't behave like the 
'variables' mentioned above, they provide for serious side-effects for 
the programmer if the coder does not think of them properly as names 
bound to objects. And that means surprises.

So, when anyone points out that Python does not have variables, but 
rather Python has names bound to objects... they are being most helpful.

As I pointed out earlier, I think the better approach would be to find 
positive language for helping new folks understand Python's beautiful 
heart, than the relatively negative language of stating Python has no 
variables.

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#71051

Mark H Harris <harrismh777@gmail.com> writes:

> So, when anyone points out that Python does not have variables, but
> rather Python has names bound to objects... they are being most
> helpful.
>
> As I pointed out earlier, I think the better approach would be to find
> positive language for helping new folks understand Python's beautiful
> heart, than the relatively negative language of stating Python has no
> variables.

You are implying a dichotomy which I don't think is useful: that
providing accurate models is “a better approach” than pointing out
existing fallacies.

Rather, the better approach IMO is to use *both*: point out existing
fallacies *and* replace them with more accurate models.

That's why I always try to say “Python doesn't have variables the way
you might know from many other languages”, *and* say “instead, it has
references bound to objects” — *in the same message*. Negative, to point
out the fallacy; positive, to provide the replacement.

Presenting an accurate model is valuable, but it's much less valuable in
isolation than pointing out that the accurate model *is superior to*,
and should replace, the existing less-accurate model in the receiver's
brain. One must necessarily use negative language to achieve that.

-- 
 \         “Religious faith is the one species of human ignorance that |
  `\     will not admit of even the *possibility* of correction.” —Sam |
_o__)                                 Harris, _The End of Faith_, 2004 |
Ben Finney

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#71054

Ben Finney <ben@benfinney.id.au>:

> That's why I always try to say “Python doesn't have variables the way
> you might know from many other languages”,

Please elaborate. To me, Python variables are like variables in all
programming languages I know. Python currently does not allow me to
obtain the "address" of a variable, but that doesn't make me think of
Python variables any differently.


Marko

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#71056

On 5/7/14 4:15 PM, Marko Rauhamaa wrote:
>> That's why I always try to say “Python doesn't have variables the way
>> you might know from many other languages”,
>
> Please elaborate. To me, Python variables are like variables in all
> programming languages I know. Python currently does not allow me to
> obtain the "address" of a variable, but that doesn't make me think of
> Python variables any differently.

Here is the difference...  in almost every other language you know.

A = macTruck
B = A

In almost every other language you know A and B each "contain" by 
reference (and almost always by static type) macTruck. But NOT python.

A --> {macTruck} <-- B


In almost every other language you know there is some kind of binding 
table (name reference to type/length) and BOTH A and B are bound to data 
in memory macTruck... and usually its a different place in memory!

NOT python.

No doubt you may use A and B in python the way other people use their 
variables in their language... but it MEANS something different.


marcus

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#71065

On Wed, 07 May 2014 16:35:00 -0500, Mark H Harris wrote:

> On 5/7/14 4:15 PM, Marko Rauhamaa wrote:
>>> That's why I always try to say “Python doesn't have variables the way
>>> you might know from many other languages”,
>>
>> Please elaborate. To me, Python variables are like variables in all
>> programming languages I know. Python currently does not allow me to
>> obtain the "address" of a variable, but that doesn't make me think of
>> Python variables any differently.
> 
> Here is the difference...  in almost every other language you know.

How do you know which languages Marko knows?

> A = macTruck
> B = A
> 
> In almost every other language you know A and B each "contain" by
> reference (and almost always by static type) macTruck. But NOT python.

Nor Javascript, Ruby, Perl, PHP, Lua, or (I think) Lisp or Java. To 
mention only a few.

I think it is easy to exaggerate the difference between Python and 
"almost every other language". Python's name binding model is very common 
amongst dynamically typed languages, and there are many dynamically typed 
languages.


If I have understood correctly, and I welcome confirmation or correction, 
one can have any combination of:

* dynamic typing and name binding (e.g. Python and Ruby);
* static typing and name binding (e.g. Java);
* dynamic typing and fixed-location variables (any examples?);
* static typing and fixed-location variables (C, Pascal).

Where do VB and Perl fit into this?


There are probably other variations as well. E.g. Cobra has both dynamic 
typed variables and static typed variables.


> In almost every other language you know there is some kind of binding
> table (name reference to type/length) and BOTH A and B are bound to data
> in memory macTruck... and usually its a different place in memory!
> 
> NOT python.

Python has "binding tables" too. They are dicts.

Any language with variables must have some way of mapping the name to the 
value. In some languages that mapping is available only to the compiler, 
and no longer exists at runtime (e.g. the assignment "x := 1;" is 
compiled to the equivalent of "copy value 1 into memory location 1234", 
with no reference to "x" remaining). In some languages the mapping is 
only available at runtime (e.g. the assignment "x := 1;" is compiled to 
the equivalent of "look up x and bind the value 1 to it"). In Python, 
lookups occur at runtime, not compile time.



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

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#71070

On Thu, May 8, 2014 at 11:27 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> If I have understood correctly, and I welcome confirmation or correction,
> one can have any combination of:
>
> * dynamic typing and name binding (e.g. Python and Ruby);
> * static typing and name binding (e.g. Java);
> * dynamic typing and fixed-location variables (any examples?);
> * static typing and fixed-location variables (C, Pascal).

Dynamic typing and fixed locations could really only be assembly
language, I think. It's all just bits in memory, and you treat them as
whatever you want. In C, signed and unsigned integers are different
types; in 80x86 assembly language, they're just integers, and you use
either JA or JG (Jump if Above vs Jump if Greater) to make unsigned or
signed comparisons. Or you can fetch a set of four bytes out of a byte
("character", ha) string and treat it as an integer - see for instance
the FOURCC system used in some audio files.

It's certainly not a normal way of writing code, but hey, it fills in
the hole in your set of four :)

ChrisA

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#71073

On Thu, 08 May 2014 12:09:21 +1000, Chris Angelico wrote:

> On Thu, May 8, 2014 at 11:27 AM, Steven D'Aprano
> <steve+comp.lang.python@pearwood.info> wrote:
>> If I have understood correctly, and I welcome confirmation or
>> correction, one can have any combination of:
>>
>> * dynamic typing and name binding (e.g. Python and Ruby); * static
>> typing and name binding (e.g. Java); * dynamic typing and
>> fixed-location variables (any examples?); * static typing and
>> fixed-location variables (C, Pascal).
> 
> Dynamic typing and fixed locations could really only be assembly
> language, I think.

Not so! That's how __slots__ and local variables work in CPython.

Objects are different sizes, so CPython can't allocate a box of a fixed 
size unless it knows how big the box needs to be. Fortunately, pointers 
are all the same size, so the object lives on the heap and the pointer 
goes in the box.

The point being, there could be a language that used fixed locations for 
variables, while still being fully dynamically typed. That would allow 
the language to use pass-by-name or pass-by-reference semantics instead 
of pass-by-value or pass-by-shared-object.




-- 
Steven

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#71074

On Thu, 08 May 2014 01:27:08 +0000, Steven D'Aprano wrote:

> If I have understood correctly, and I welcome confirmation or
> correction, one can have any combination of:

> * dynamic typing and name binding (e.g. Python and Ruby);
> * static typing and name binding (e.g. Java);
> * dynamic typing and fixed-location variables (any examples?);
> * static typing and fixed-location variables (C, Pascal).

C unions, if you squint just right, are fixed location variables and at
least partially dynamic, within the bounds of what you define at compile
time.

And at the risk of opening another can of worms, C's typing is
sufficiently weak that it can be way more dynamic than many programmers
want.  It's this |↔| close to assembly language (ChrisA's example of the
combination of dynamic typing and fixed locations).

Dan

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#71199

On 5/7/14 8:27 PM, Steven D'Aprano wrote:
>> In almost every other language you know A and B each "contain" by
>> reference (and almost always by static type) macTruck. But NOT python.
>
> Nor Javascript, Ruby, Perl, PHP, Lua, or (I think) Lisp or Java. To
> mention only a few.
>
> I think it is easy to exaggerate the difference between Python and
> "almost every other language". Python's name binding model is very common
> amongst dynamically typed languages, and there are many dynamically typed
> languages.

     Then we don't need a discussion.

     Why are new Python coders 'always' confused by this question of 
variable (name value) vs. {name: object} model of Python?

     The reason I suggest is that the person has a preconceived idea of 
what 'variable' means, and they then attempt to apply their conception 
of variable on to Python in some way ending in a surprise.

     We need a way to speak about Pythons name object model to avoid 
this confusion.

marcus

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#71209

On Fri, 09 May 2014 17:34:17 -0500, Mark H Harris wrote:

> On 5/7/14 8:27 PM, Steven D'Aprano wrote:
>>> In almost every other language you know A and B each "contain" by
>>> reference (and almost always by static type) macTruck. But NOT python.
>>
>> Nor Javascript, Ruby, Perl, PHP, Lua, or (I think) Lisp or Java. To
>> mention only a few.
>>
>> I think it is easy to exaggerate the difference between Python and
>> "almost every other language". Python's name binding model is very
>> common amongst dynamically typed languages, and there are many
>> dynamically typed languages.
> 
>      Then we don't need a discussion.
> 
>      Why are new Python coders 'always' confused by this question of
> variable (name value) vs. {name: object} model of Python?

"Always"? I don't think anyone, not even Ben, claims that new Python 
coders are "always" confused about Python's variable semantics. That 
would be a straw man, easy to disprove by just finding a single person 
who wasn't confused. Perhaps someone who had never learned C and didn't 
know C variable semantics?


>      The reason I suggest is that the person has a preconceived idea of
> what 'variable' means, and they then attempt to apply their conception
> of variable on to Python in some way ending in a surprise.

That's the problem as some of us see it.


>      We need a way to speak about Pythons name object model to avoid
> this confusion.

And that would be the "name binding" part.




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

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#71229

On 05/09/2014 06:11 PM, Steven D'Aprano wrote:
> On Fri, 09 May 2014 17:34:17 -0500, Mark H Harris wrote:
>
>> On 5/7/14 8:27 PM, Steven D'Aprano wrote:
<snip>
>>       Why are new Python coders 'always' confused by this question of
>> variable (name value) vs. {name: object} model of Python?
>
> "Always"? I don't think anyone, not even Ben, claims that new Python
> coders are "always" confused about Python's variable semantics. That
> would be a straw man, easy to disprove by just finding a single person
> who wasn't confused. Perhaps someone who had never learned C and didn't
> know C variable semantics?
>

Well, here is that one person.   ;-)

I'm an entirely self-taught amateur/hobbyist programmer, coming to Python from a C background. 
Very early in my reading of books/tutorials on Python I learned that Python variables are 
different, and how they are different from C variables.  Essentially I said, "Okay, they're 
different.  What's next?"  There was no confusion at all.  All I had to do was accept that they 
_are_ different.  (BTW, I'm now quite hooked on Python -- and still learning it.)

>>       The reason I suggest is that the person has a preconceived idea of
>> what 'variable' means, and they then attempt to apply their conception
>> of variable on to Python in some way ending in a surprise.
>
> That's the problem as some of us see it.
>

As I said above, not a problem.  I already accepted the fact that all programming languages are 
different -- often with similarities, but more often quite different, especially in the details. 
  So when programming in C I think in C-style variables, in Python I think in Python-style 
variables.  And uv course, I nefer make mmistakes...  Yeah, right!    ;-)

>
>>       We need a way to speak about Pythons name object model to avoid
>> this confusion.
>
> And that would be the "name binding" part.
>

This is something I absolutely disagree with.  I still think it's only necessary to teach that 
variables in different languages are handled differently.  Insisting on a different name is NOT 
helpful.  And insisting that Python does not have variables is ludicrous!

      -=- Larry -=-

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