Re: (test) ? a:b

Date	2014-10-25 19:04 -0600
From	Michael Torrie <torriem@gmail.com>
Subject	Re: (test) ? a:b
References	<54476af8$0$21651$426a74cc@news.free.fr> <7839376e-fc27-4299-ae63-4ddf17ef9a8a@googlegroups.com> <m27skn$2e2$1@ger.gmane.org> <mailman.15062.1413971583.18130.python-list@python.org> <carc00FdrboU1@mid.individual.net>
Newsgroups	comp.lang.python
Message-ID	<mailman.15184.1414285521.18130.python-list@python.org> (permalink)

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On 10/22/2014 09:46 PM, Gregory Ewing wrote:
> Chris Angelico wrote:
>> I've seen much MUCH worse... where multiple conditional
>> expressions get combined arithmetically, and then the result used
>> somewhere...
> 
> In the days of old-school BASIC it was common to
> exploit the fact that boolean expressions evaluated
> to 0 or 1 (or -1, depending on your dialect :) to
> achieve conditional expressions or other tricks.

As far as I can tell, no BASIC dialect I've looked at (DOS and Linux
worlds only), has ever had any logical operators like AND (&&), OR (||),
and NOT (!).  They only appear to have bitwise operators (&,|,~ C
equivalent).  The fact that comparison operators returned 0 and -1 made
the bitwise operators function the same as logical.  But you can run
into trouble if you tried to use a common python idiom like this:

x = read_some_lines() 'returns number of lines read, or zero if none are
if not x:
	print ("I couldn't read any lines")
	exit(1)

Basically any value other than -1 for x would cause the not x to be
true.  Off topic, and no matter to python programmers.  But for BASIC
you need to watch out for this.  One BASIC dialect introduced a set of
functions, istrue() and isfalse() to convert a non-zero truth value to
-1, and any falsish value to zero (like maybe an empty string).  That
way the bitwise operators would always function as logical operators in
a conditional expression.

Thread

(test) ? a:b "ast" <nomail@invalid.com> - 2014-10-22 10:29 +0200
  Re: (test) ? a:b buscacio@gmail.com - 2014-10-22 02:05 -0700
    Re: (test) ? a:b "ast" <nomail@invalid.com> - 2014-10-22 11:14 +0200
      Re: (test) ? a:b Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-10-22 12:45 +0100
        Re: (test) ? a:b "ast" <nomail@invalid.com> - 2014-10-27 09:01 +0100
      Re: (test) ? a:b Michael Torrie <torriem@gmail.com> - 2014-10-22 11:16 -0600
        Re: (test) ? a:b Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-10-23 11:44 +1100
    Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-22 20:15 +1100
    Re: (test) ? a:b Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-10-22 10:16 +0100
    Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-22 20:27 +1100
      Re: (test) ? a:b Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-10-23 16:46 +1300
        Re: (test) ? a:b MRAB <python@mrabarnett.plus.com> - 2014-10-23 11:12 +0100
          Re: (test) ? a:b "ast" <nomail@invalid.com> - 2014-10-24 08:38 +0200
        Re: (test) ? a:b Michael Torrie <torriem@gmail.com> - 2014-10-25 19:04 -0600
          Re: (test) ? a:b Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-10-27 22:04 +1300
        Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-26 12:20 +1100
        Re: (test) ? a:b Michael Torrie <torriem@gmail.com> - 2014-10-25 21:05 -0600
    Re: (test) ? a:b Ned Batchelder <ned@nedbatchelder.com> - 2014-10-22 07:30 -0400
      Re: (test) ? a:b Marko Rauhamaa <marko@pacujo.net> - 2014-10-22 14:41 +0300
      Re: (test) ? a:b Rustom Mody <rustompmody@gmail.com> - 2014-10-22 06:16 -0700
        Re: (test) ? a:b "BartC" <bc@freeuk.com> - 2014-10-22 19:08 +0100
          Re: (test) ? a:b Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-10-22 19:55 -0400
            Re: (test) ? a:b "BartC" <bc@freeuk.com> - 2014-10-23 11:50 +0100
              Re: (test) ? a:b Marko Rauhamaa <marko@pacujo.net> - 2014-10-23 16:44 +0300
                Re: (test) ? a:b Ian Kelly <ian.g.kelly@gmail.com> - 2014-10-23 08:24 -0600
                Re: (test) ? a:b Alain Ketterlin <alain@dpt-info.u-strasbg.fr> - 2014-10-23 16:41 +0200
                Re: (test) ? a:b Marko Rauhamaa <marko@pacujo.net> - 2014-10-23 19:20 +0300
                Re: (test) ? a:b Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-10-24 19:38 +1100
                Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-24 19:45 +1100
                Re: (test) ? a:b Marko Rauhamaa <marko@pacujo.net> - 2014-10-24 12:37 +0300
                Re: (test) ? a:b Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-10-25 00:07 +1100
                Re: (test) ? a:b Ian Kelly <ian.g.kelly@gmail.com> - 2014-10-24 12:22 -0600
                Re: (test) ? a:b Marko Rauhamaa <marko@pacujo.net> - 2014-10-24 21:46 +0300
                Re: (test) ? a:b Dan Stromberg <drsalists@gmail.com> - 2014-10-24 10:20 -0700
                Re: (test) ? a:b alister <alister.nospam.ware@ntlworld.com> - 2014-10-24 20:58 +0000
                Re: (test) ? a:b Marko Rauhamaa <marko@pacujo.net> - 2014-10-25 00:02 +0300
                Re: (test) ? a:b Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-10-25 16:03 +1100
                Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-25 16:25 +1100
                Re: (test) ? a:b Ned Batchelder <ned@nedbatchelder.com> - 2014-10-25 07:58 -0400
                Re: (test) ? a:b Ian Kelly <ian.g.kelly@gmail.com> - 2014-10-25 07:53 -0600
                Re: (test) ? a:b Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-10-25 14:11 -0400
                Re: (test) ? a:b alister <alister.nospam.ware@ntlworld.com> - 2014-10-25 19:49 +0000
                Re: (test) ? a:b Ben Finney <ben+python@benfinney.id.au> - 2014-10-26 07:45 +1100
                Re: (test) ? a:b Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-10-26 11:10 +1100
                Re: (test) ? a:b Ben Finney <ben+python@benfinney.id.au> - 2014-10-26 12:03 +1100
                Re: (test) ? a:b Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-10-26 15:15 +1100
                Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-26 15:34 +1100
                Re: (test) ? a:b Terry Reedy <tjreedy@udel.edu> - 2014-10-26 17:12 -0400
                Re: (test) ? a:b Ben Finney <ben+python@benfinney.id.au> - 2014-10-27 11:38 +1100
                Re: (test) ? a:b MRAB <python@mrabarnett.plus.com> - 2014-10-27 01:40 +0000
                Re: (test) ? a:b Rustom Mody <rustompmody@gmail.com> - 2014-10-26 19:19 -0700
                Re: (test) ? a:b Ben Finney <ben+python@benfinney.id.au> - 2014-10-26 12:10 +1100
                Re: (test) ? a:b Joshua Landau <joshua@landau.ws> - 2014-10-27 01:55 +0000
                Re: (test) ? a:b Ben Finney <ben+python@benfinney.id.au> - 2014-10-27 13:28 +1100
                Re: (test) ? a:b Rustom Mody <rustompmody@gmail.com> - 2014-10-26 19:38 -0700
                Re: (test) ? a:b Joshua Landau <joshua@landau.ws> - 2014-10-27 02:43 +0000
                Re: (test) ? a:b Ben Finney <ben+python@benfinney.id.au> - 2014-10-27 13:56 +1100
                Re: (test) ? a:b Dan Stromberg <drsalists@gmail.com> - 2014-10-25 15:34 -0700
                Re: (test) ? a:b Ben Finney <ben+python@benfinney.id.au> - 2014-10-26 10:53 +1100
                Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-26 11:01 +1100
                Re: (test) ? a:b Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-10-26 01:09 +0100
                Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-26 11:13 +1100
          Re: (test) ? a:b Vito De Tullio <vito.detullio@gmail.com> - 2014-10-23 06:55 +0200
      Re: (test) ? a:b Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-10-23 03:28 +1100
        Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-23 03:40 +1100
        Re: (test) ? a:b alister <alister.nospam.ware@ntlworld.com> - 2014-10-22 18:03 +0000
        Re: (test) ? a:b Matthew Ruffalo <mmr15@case.edu> - 2014-10-22 14:27 -0400
        Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-23 05:30 +1100
        Re: (test) ? a:b Ned Batchelder <ned@nedbatchelder.com> - 2014-10-22 16:11 -0400
    Re: (test) ? a:b Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-10-22 12:41 +0100
      Re: (test) ? a:b alister <alister.nospam.ware@ntlworld.com> - 2014-10-22 15:12 +0000
        Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-23 02:18 +1100
          Re: (test) ? a:b alister <alister.nospam.ware@ntlworld.com> - 2014-10-22 15:24 +0000
    Re: (test) ? a:b Dan Stromberg <drsalists@gmail.com> - 2014-10-22 09:09 -0700
  Re: (test) ? a:b Tobiah <toby@tobiah.org> - 2014-10-24 10:23 -0700
    Re: (test) ? a:b Chris Angelico <rosuav@gmail.com> - 2014-10-25 04:27 +1100
      Re: (test) ? a:b Tobiah <toby@tobiah.org> - 2014-10-24 11:31 -0700

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