Re: Assignment Versus Equality

From	Chris Angelico <rosuav@gmail.com>
Newsgroups	comp.lang.python
Subject	Re: Assignment Versus Equality
Date	2016-06-28 20:34 +1000
Message-ID	<mailman.70.1467110107.2358.python-list@python.org> (permalink)
References	(14 earlier) <3bd25897-8ecb-4a27-ab22-220677551f41@googlegroups.com> <CAPTjJmp0+CMYg=nTi+dkB1Wo1XK-of7MjvfiShSnn-gd7sin9g@mail.gmail.com> <mailman.65.1467098776.2358.python-list@python.org> <01ed522b-71d6-4535-8d49-b0e32c33ee3a@googlegroups.com> <CAPTjJmq1y+J2bi4FtciErBX-i09fvcxePwa4WUBM0=6aVWn+fw@mail.gmail.com>

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On Tue, Jun 28, 2016 at 6:49 PM, Lawrence D’Oliveiro
<lawrencedo99@gmail.com> wrote:
> On Tuesday, June 28, 2016 at 7:26:30 PM UTC+12, Chris Angelico wrote:
>> Why not:
>>
>> if (error) goto cleanup;
>> ...
>> cleanup:
>> do_cleanup;
>
> They all fall into that same trap. Doesn’t scale. Try one with allocation inside a loop, e.g. lines 488 onwards.

How is that different? You can use a goto inside a for loop just fine.
(You can even, if you are absolutely insane and begging to be murdered
by the future maintainer, use a goto outside a for loop targeting a
label inside. See for example Duff's Device, although that's a switch
rather than an actual goto.) You have a loop, and inside that loop,
the exact same error handling pattern; so it should be possible to
perform the exact same transformation, albeit with a differently-named
local cleanup label.

So, yes. It doesn't scale, if by "scale" you mean "so many separate
local instances of error handling that you lose track of your cleanup
labels". But you should be able to keep half a dozen labels in your
head (if they're named appropriately), and if you have that many local
error handlers, you probably want something to be refactored.

ChrisA

Thread

Assignment Versus Equality Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-26 00:36 -0700
  Re: Assignment Versus Equality BartC <bc@freeuk.com> - 2016-06-26 11:48 +0100
    Re: Assignment Versus Equality Steven D'Aprano <steve@pearwood.info> - 2016-06-26 23:21 +1000
      Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-26 07:26 -0700
        Re: Assignment Versus Equality Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-06-26 11:31 -0400
      Re: Assignment Versus Equality Christopher Reimer <christopher_reimer@icloud.com> - 2016-06-26 11:47 -0700
      Re: Assignment Versus Equality Michael Torrie <torriem@gmail.com> - 2016-06-26 15:28 -0600
      Re: Assignment Versus Equality Bob Gailer <bgailer@gmail.com> - 2016-06-27 08:22 -0400
        Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-27 05:48 -0700
          Re: Assignment Versus Equality Steven D'Aprano <steve@pearwood.info> - 2016-06-27 23:28 +1000
            Re: Assignment Versus Equality Marko Rauhamaa <marko@pacujo.net> - 2016-06-27 16:58 +0300
            Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-27 07:23 -0700
              Re: Assignment Versus Equality Steven D'Aprano <steve@pearwood.info> - 2016-06-28 11:05 +1000
                Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-27 21:31 -0700
                Re: Assignment Versus Equality Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-06-28 15:42 +1000
                Re: Assignment Versus Equality Chris Angelico <rosuav@gmail.com> - 2016-06-28 16:04 +1000
                Re: Assignment Versus Equality Marko Rauhamaa <marko@pacujo.net> - 2016-06-28 09:12 +0300
                Re: Assignment Versus Equality Jussi Piitulainen <jussi.piitulainen@helsinki.fi> - 2016-06-28 11:04 +0300
                Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-27 23:09 -0700
                Re: Assignment Versus Equality Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-28 00:12 -0700
                Re: Assignment Versus Equality Chris Angelico <rosuav@gmail.com> - 2016-06-28 17:26 +1000
                Re: Assignment Versus Equality Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-28 01:49 -0700
                Re: Assignment Versus Equality Chris Angelico <rosuav@gmail.com> - 2016-06-28 20:34 +1000
                Re: Assignment Versus Equality Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-28 17:42 -0700
                Re: Assignment Versus Equality Random832 <random832@fastmail.com> - 2016-06-28 10:13 -0400
                Re: Assignment Versus Equality Marko Rauhamaa <marko@pacujo.net> - 2016-06-28 19:39 +0300
                Re: Assignment Versus Equality Marko Rauhamaa <marko@pacujo.net> - 2016-06-28 19:41 +0300
                Re: Assignment Versus Equality Random832 <random832@fastmail.com> - 2016-06-28 13:19 -0400
                Re: Assignment Versus Equality Ian Kelly <ian.g.kelly@gmail.com> - 2016-06-28 12:27 -0600
                Re: Assignment Versus Equality Marko Rauhamaa <marko@pacujo.net> - 2016-06-28 22:40 +0300
                Re: Assignment Versus Equality Gene Heskett <gheskett@shentel.net> - 2016-06-28 16:59 -0400
                Re: Assignment Versus Equality Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-06-30 12:29 +1200
                Re: Assignment Versus Equality Steven D'Aprano <steve@pearwood.info> - 2016-06-30 12:50 +1000
                Re: Assignment Versus Equality Marko Rauhamaa <marko@pacujo.net> - 2016-06-30 09:22 +0300
                Re: Assignment Versus Equality Steven D'Aprano <steve@pearwood.info> - 2016-06-29 12:27 +1000
                Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-28 20:52 -0700
                Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-28 21:03 -0700
                Re: Assignment Versus Equality Random832 <random832@fastmail.com> - 2016-06-29 00:52 -0400
              Re: Assignment Versus Equality Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-27 18:14 -0700
            Re: Assignment Versus Equality Gene Heskett <gheskett@shentel.net> - 2016-06-27 11:21 -0400
          Re: Assignment Versus Equality Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-06-27 20:04 -0400
    Re: Assignment Versus Equality Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-06-26 11:21 -0400
      Re: Assignment Versus Equality Cousin Stanley <HooDunnit@didly42KahZidly.net> - 2016-06-26 08:47 -0700
        Re: Assignment Versus Equality BartC <bc@freeuk.com> - 2016-06-26 16:56 +0100
          Re: Assignment Versus Equality Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-06-27 11:38 +1200
          Re: Assignment Versus Equality Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-06-27 07:30 -0400
            Re: Assignment Versus Equality Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-06-28 18:17 +1200
          Re: Assignment Versus Equality Grant Edwards <grant.b.edwards@gmail.com> - 2016-06-27 13:59 +0000
            Re: Assignment Versus Equality Marko Rauhamaa <marko@pacujo.net> - 2016-06-27 17:09 +0300
              Re: Assignment Versus Equality sohcahtoa82@gmail.com - 2016-06-27 17:33 -0700
                Re: Assignment Versus Equality Marko Rauhamaa <marko@pacujo.net> - 2016-06-28 07:25 +0300
                Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-27 23:54 -0700
            Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-27 07:10 -0700
              Re: Assignment Versus Equality Steven D'Aprano <steve@pearwood.info> - 2016-06-29 12:35 +1000
                Re: Assignment Versus Equality Chris Angelico <rosuav@gmail.com> - 2016-06-29 14:19 +1000
                Re: Assignment Versus Equality Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-28 21:51 -0700
                Re: Assignment Versus Equality Chris Angelico <rosuav@gmail.com> - 2016-06-29 15:07 +1000
                Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-28 22:55 -0700
                Re: Assignment Versus Equality Chris Angelico <rosuav@gmail.com> - 2016-06-29 16:26 +1000
                Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-28 23:33 -0700
                Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-28 23:37 -0700
                Re: Assignment Versus Equality Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-06-29 15:26 +1000
                Re: Assignment Versus Equality Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-28 22:51 -0700
                Re: Assignment Versus Equality Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2016-06-29 16:45 +1000
                Re: Assignment Versus Equality Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-29 01:07 -0700
                Re: Assignment Versus Equality Chris Angelico <rosuav@gmail.com> - 2016-06-29 18:09 +1000
                Re: Assignment Versus Equality Steven D'Aprano <steve@pearwood.info> - 2016-06-29 22:36 +1000
                Re: Assignment Versus Equality BartC <bc@freeuk.com> - 2016-06-29 14:24 +0100
                Re: Assignment Versus Equality Chris Angelico <rosuav@gmail.com> - 2016-06-29 23:35 +1000
                Re: Assignment Versus Equality BartC <bc@freeuk.com> - 2016-06-29 15:47 +0100
                Re: Assignment Versus Equality Chris Angelico <rosuav@gmail.com> - 2016-06-29 23:34 +1000
                Re: Assignment Versus Equality BartC <bc@freeuk.com> - 2016-06-29 10:49 +0100
                Re: Assignment Versus Equality Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-29 02:56 -0700
                Re: Assignment Versus Equality BartC <bc@freeuk.com> - 2016-06-29 11:10 +0100
                Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-29 03:24 -0700
            Re: Assignment Versus Equality Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid> - 2016-06-27 16:48 +0200
              Re: Assignment Versus Equality Rustom Mody <rustompmody@gmail.com> - 2016-06-27 22:00 -0700
            Re: Assignment Versus Equality Steven D'Aprano <steve@pearwood.info> - 2016-06-28 11:34 +1000
          Re: Assignment Versus Equality MRAB <python@mrabarnett.plus.com> - 2016-06-27 16:27 +0100
            Re: Assignment Versus Equality Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-27 14:56 -0700
            Re: Assignment Versus Equality Lawrence D’Oliveiro <lawrencedo99@gmail.com> - 2016-06-27 15:45 -0700
              Re: Assignment Versus Equality BartC <bc@freeuk.com> - 2016-06-28 00:08 +0100
                Re: Assignment Versus Equality Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2016-06-27 20:11 -0400
                Re: Assignment Versus Equality BartC <bc@freeuk.com> - 2016-06-28 11:35 +0100
                Re: Assignment Versus Equality Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-06-28 18:59 +1200
            Re: Assignment Versus Equality Steven D'Aprano <steve@pearwood.info> - 2016-06-28 11:28 +1000
          Re: Assignment Versus Equality Grant Edwards <grant.b.edwards@gmail.com> - 2016-06-27 15:42 +0000
      Re: Assignment Versus Equality Marko Rauhamaa <marko@pacujo.net> - 2016-06-26 19:11 +0300
    Re: Assignment Versus Equality MRAB <python@mrabarnett.plus.com> - 2016-06-26 16:41 +0100
      Re: Assignment Versus Equality BartC <bc@freeuk.com> - 2016-06-26 17:08 +0100
    Re: Assignment Versus Equality Christopher Reimer <christopher_reimer@icloud.com> - 2016-06-26 11:53 -0700
      Re: Assignment Versus Equality Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-06-27 11:41 +1200
    Re: Assignment Versus Equality Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-06-27 11:22 +1200
      Re: Assignment Versus Equality BartC <bc@freeuk.com> - 2016-06-27 00:39 +0100
        Re: Assignment Versus Equality Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2016-06-28 18:15 +1200

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