Re: code review

Date	2012-07-01 09:35 +0200
From	Thomas Jollans <t@jollybox.de>
Subject	Re: code review
References	(10 earlier) <87wr2oecf6.fsf@dpt-info.u-strasbg.fr> <4FEF7117.7000109@jollybox.de> <jsns6l$7c0$1@dough.gmane.org> <mailman.1663.1341093928.4697.python-list@python.org> <4fefb0ad$0$29988$c3e8da3$5496439d@news.astraweb.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.1677.1341128143.4697.python-list@python.org> (permalink)

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On 07/01/2012 04:06 AM, Steven D'Aprano wrote:
> On Sun, 01 Jul 2012 00:05:26 +0200, Thomas Jollans wrote:
> 
>> As soon as you read it as a ternary operator, 
> 
> Well that's your problem. Why are you reading it as a ternary operator? 
> It isn't one. It is a pair of chained binary operator.
> 
> How can you tell that it is a pair of binary operators, rather than a 
> single ternary operator?
> 
> 1) There are TWO operators, hence a pair, not a single ternary operator;
> 
> 2) each operator takes TWO arguments, not three.

This is simply wrong. The comparisons are not acting as binary operators.

> You can't just arbitrarily stick parentheses around parts of expressions
> and expect the result to remain unchanged. Order of evaluation matters:
>
> 2**3**4 != (2**3)**4
>
> Comparisons are no different. You can't just toss in some arbitrary
> brackets and expect the result to be the same. In the second case, the
> parentheses explicitly turn the comparison into the equivalent of this:

As Chris points out, 2**3**4 == 2**(3**4)

For any chain of actual binary operators, it is possible to place
brackets around binary sub-expressions such that the meaning of the
total expression stays the same. This is true of ALL infix-notated
strictly binary operators. This is not true of Python comparison operators.

If you're inclined to look at operators in terms of how many arguments
they take, then the inescapable conclusion is that a chain of N
comparison operators forms one single (N+1)-term operator because it
cannot be grouped into binary expressions without rephrasing the
expression using "and".

Thread

code review "Littlefield, Tyler" <tyler@tysdomain.com> - 2012-06-28 20:57 -0600
  Re: code review alex23 <wuwei23@gmail.com> - 2012-06-28 20:58 -0700
    Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-06-29 07:31 +0000
      Re: code review Chris Angelico <rosuav@gmail.com> - 2012-06-29 17:42 +1000
      Re: code review "Littlefield, Tyler" <tyler@tysdomain.com> - 2012-06-29 09:03 -0600
        Re: code review Alister <alister.ware@ntlworld.com> - 2012-06-29 19:41 +0000
          Re: code review MRAB <python@mrabarnett.plus.com> - 2012-06-29 21:09 +0100
          Re: code review "Martin P. Hellwig" <martin.hellwig@gmail.com> - 2012-06-29 13:27 -0700
            Re: code review Alister <alister.ware@ntlworld.com> - 2012-06-29 20:43 +0000
              Re: code review Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-06-29 19:02 -0400
              Re: code review Terry Reedy <tjreedy@udel.edu> - 2012-06-29 23:02 -0400
          Re: code review "Littlefield, Tyler" <tyler@tysdomain.com> - 2012-06-29 14:49 -0600
            Re: code review Alister <alister.ware@ntlworld.com> - 2012-06-30 09:31 +0000
              Re: code review Alister <alister.ware@ntlworld.com> - 2012-06-30 09:36 +0000
          Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-06-30 02:28 +0000
            Re: code review Alister <alister.ware@ntlworld.com> - 2012-06-30 09:22 +0000
          Re: code review Terry Reedy <tjreedy@udel.edu> - 2012-06-29 23:00 -0400
        Re: code review Alister <alister.ware@ntlworld.com> - 2012-06-30 10:04 +0000
          Re: code review Peter Otten <__peter__@web.de> - 2012-06-30 12:29 +0200
            Re: code review Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-06-30 20:39 +0200
              Re: code review Thomas Jollans <t@jollybox.de> - 2012-06-30 21:38 +0200
                Re: code review Alister <alister.ware@ntlworld.com> - 2012-06-30 20:30 +0000
                Re: code review Thomas Jollans <t@jollybox.de> - 2012-06-30 22:50 +0200
                Re: code review Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2012-06-30 23:07 +0200
                Re: code review Thomas Jollans <t@jollybox.de> - 2012-06-30 23:35 +0200
                Re: code review Terry Reedy <tjreedy@udel.edu> - 2012-06-30 17:47 -0400
                Re: code review Thomas Jollans <t@jollybox.de> - 2012-07-01 00:05 +0200
                Re: code review Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2012-07-01 01:03 +0200
                Re: code review Ben Finney <ben+python@benfinney.id.au> - 2012-07-01 10:08 +1000
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-01 10:37 +1000
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-01 03:23 +0000
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-01 13:48 +1000
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-01 06:54 +0000
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-01 16:59 +1000
                Re: code review Terry Reedy <tjreedy@udel.edu> - 2012-07-01 05:55 -0400
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-02 01:26 +0000
                Re: code review Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-13 12:30 +0000
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-13 15:04 +0000
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-14 01:36 +1000
                Re: code review rusi <rustompmody@gmail.com> - 2012-07-13 09:24 -0700
                Re: code review Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-07-13 16:39 -0400
                Re: code review Duncan Booth <duncan.booth@invalid.invalid> - 2012-07-16 10:43 +0000
                Re: code review Ben Finney <ben+python@benfinney.id.au> - 2012-07-16 21:34 +1000
                Re: code review Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-17 10:54 +0000
                Re: code review Terry Reedy <tjreedy@udel.edu> - 2012-07-13 19:09 -0400
                Re: code review Ian Kelly <ian.g.kelly@gmail.com> - 2012-07-14 03:26 -0600
                Re: code review Terry Reedy <tjreedy@udel.edu> - 2012-07-14 16:42 -0400
                Re: code review rusi <rustompmody@gmail.com> - 2012-06-30 21:07 -0700
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-01 14:20 +1000
                Re: code review Ben Finney <ben+python@benfinney.id.au> - 2012-07-01 17:28 +1000
                Re: code review Thomas Jollans <t@jollybox.de> - 2012-07-01 09:46 +0200
                Re: code review HoneyMonster <nobody@someplace.invalid> - 2012-07-01 20:53 +0000
                Re: code review Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-07-01 05:18 -0400
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-02 00:41 +0000
                Re: code review Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-07-01 21:40 -0400
                Re: code review Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-07-01 13:41 -0400
                Re: code review John O'Hagan <research@johnohagan.com> - 2012-07-02 14:43 +1000
                Re: Re: code review Evan Driscoll <driscoll@cs.wisc.edu> - 2012-06-30 23:45 -0500
                Re: Re: code review Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-07-01 08:57 +0200
                Re: code review Alister <alister.ware@ntlworld.com> - 2012-07-01 09:54 +0000
                Re: Re: code review Evan Driscoll <driscoll@cs.wisc.edu> - 2012-07-01 10:48 -0500
                Re: Re: code review lars van gemerden <lars@rational-it.com> - 2012-07-06 04:22 -0700
                Re: Re: code review lars van gemerden <lars@rational-it.com> - 2012-07-06 04:22 -0700
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-06 13:58 +0000
                Re: code review Roy Smith <roy@panix.com> - 2012-07-13 08:32 -0700
                Re: code review Evan Driscoll <driscoll@cs.wisc.edu> - 2012-06-30 23:57 -0500
                Re: code review Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-07-01 09:04 +0200
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-01 02:06 +0000
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-01 12:20 +1000
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-01 04:17 +0000
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-01 14:23 +1000
                Re: code review Steven D'Aprano <steve+usenet@pearwood.info> - 2012-07-01 06:27 +0000
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-01 16:33 +1000
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-02 01:28 +0000
                Re: code review Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-07-01 21:50 -0400
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-02 07:29 +0000
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-02 12:04 +1000
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-02 08:11 +0000
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-02 18:20 +1000
                Re: code review Rick Johnson <rantingrickjohnson@gmail.com> - 2012-07-02 08:57 -0700
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-03 02:42 +1000
                Re: code review Rick Johnson <rantingrickjohnson@gmail.com> - 2012-07-02 11:22 -0700
                Re: code review Thomas Jollans <t@jollybox.de> - 2012-07-02 21:06 +0200
                Re: code review Rick Johnson <rantingrickjohnson@gmail.com> - 2012-07-02 12:35 -0700
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-03 07:57 +1000
                Re: code review Neil Cerutti <neilc@norwich.edu> - 2012-07-03 12:19 +0000
                Re: code review Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-07-02 01:20 -0400
                Re: code review Thomas Jollans <t@jollybox.de> - 2012-07-02 16:41 +0200
                Re: code review Terry Reedy <tjreedy@udel.edu> - 2012-07-02 11:33 -0400
                Re: code review Thomas Jollans <t@jollybox.de> - 2012-07-01 09:35 +0200
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-02 00:43 +0000
                Re: code review Thomas Jollans <t@jollybox.de> - 2012-07-02 16:26 +0200
                Re: code review Rick Johnson <rantingrickjohnson@gmail.com> - 2012-07-02 08:16 -0700
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-03 02:55 +1000
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-03 00:57 +0000
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-03 11:22 +1000
                Re: code review John O'Hagan <research@johnohagan.com> - 2012-07-03 12:25 +1000
                Re: code review Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-03 04:11 +0000
                Re: code review Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-07-03 02:09 -0400
                Re: code review Roy Smith <roy@panix.com> - 2012-07-03 08:33 -0400
                Re: code review Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-03 16:53 +0100
                Re: code review Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-07-03 17:32 -0400
                Re: code review rusi <rustompmody@gmail.com> - 2012-07-02 22:10 -0700
                Re: code review Ben Finney <ben+python@benfinney.id.au> - 2012-07-03 15:46 +1000
                Re: code review John O'Hagan <research@johnohagan.com> - 2012-07-04 00:59 +1000
                Re: code review Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-03 16:50 +0100
                Re: code review Paul Rudin <paul.nospam@rudin.co.uk> - 2012-07-04 10:29 +0100
                Re: code review Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-04 17:25 +0100
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-04 01:53 +1000
                Re: code review Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-03 17:05 +0100
                Re: code review Dave Angel <d@davea.name> - 2012-07-03 16:13 -0400
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-04 07:54 +1000
                Re: code review Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-04 09:28 +0100
                Re: code review rusi <rustompmody@gmail.com> - 2012-06-30 19:37 -0700
                Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-01 09:25 +1000
                Re: code review Thomas Jollans <t@jollybox.de> - 2012-07-01 01:50 +0200
                Re: code review "Martin P. Hellwig" <martin.hellwig@gmail.com> - 2012-06-30 14:48 -0700
                Re: code review Ian Kelly <ian.g.kelly@gmail.com> - 2012-07-02 13:16 -0600
            Re: code review Alister <alister.ware@ntlworld.com> - 2012-06-30 20:25 +0000
          Re: code review Kushal Kumaran <kushal.kumaran+python@gmail.com> - 2012-07-03 23:23 +0530
            Re: code review John Gordon <gordon@panix.com> - 2012-07-03 18:18 +0000
              Re: code review Ian Kelly <ian.g.kelly@gmail.com> - 2012-07-03 12:27 -0600
              Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-04 07:51 +1000
          Re: code review Ian Kelly <ian.g.kelly@gmail.com> - 2012-07-03 12:19 -0600
          Re: code review kushal.kumaran+python@gmail.com - 2012-07-04 08:27 +0530
          Re: code review Chris Angelico <rosuav@gmail.com> - 2012-07-04 13:53 +1000
          Re: code review Simon Cropper <simoncropper@fossworkflowguides.com> - 2012-07-04 14:55 +1000
          Re: code review "Littlefield, Tyler" <tyler@tysdomain.com> - 2012-07-03 23:39 -0600
            Re: code review alex23 <wuwei23@gmail.com> - 2012-07-03 23:17 -0700
              Re: code review rusi <rustompmody@gmail.com> - 2012-07-04 00:05 -0700
          Apology for OT posts (was: code review) John O'Hagan <research@johnohagan.com> - 2012-07-06 12:06 +1000
          Re: Apology for OT posts Simon Cropper <simoncropper@fossworkflowguides.com> - 2012-07-06 15:30 +1000
          Re: Apology for OT posts Chris Angelico <rosuav@gmail.com> - 2012-07-06 17:45 +1000
          Re: Apology for OT posts Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-06 10:37 +0100

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