Re: (test) ? a:b

From	Marko Rauhamaa <marko@pacujo.net>
Newsgroups	comp.lang.python
Subject	Re: (test) ? a:b
Date	2014-10-23 16:44 +0300
Organization	A noiseless patient Spider
Message-ID	<878uk6x5nd.fsf@elektro.pacujo.net> (permalink)
References	(2 earlier) <mailman.15068.1413977455.18130.python-list@python.org> <7d2ea3c1-504e-4f5c-8338-501b1483df38@googlegroups.com> <HqS1w.770817$AB3.493052@fx07.am4> <mailman.15097.1414022143.18130.python-list@python.org> <M452w.582708$Ym.533586@fx05.am4>

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"BartC" <bc@freeuk.com>:

>> Ah, but what would
>>
>> x = [f, g][cond]()
>>
>> produce?
>
> It will select f or g (which should refer to functions), and call one of
> those depending on cond. That's not a problem.
>
> The problem is it will still evaluate both f and g,

That's not really the problem. The problem is in readability.

However, the "[f, g][cond]()" technique is how pure lambda calculus
implements conditional branching so it is interesting in its own right.
IOW, you can do "short-circuiting" in purely functional programming:

    j = j + 1 if j < 10 else 3

    <=>

    j = (lambda: 3, lambda: j + 1)[j < 10]()


Marko

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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