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Groups > comp.lang.python > #25548

Re: Encapsulation, inheritance and polymorphism

From Andrew Cooper <amc96@cam.ac.uk>
Newsgroups comp.lang.python
Subject Re: Encapsulation, inheritance and polymorphism
References (4 earlier) <FNKdnU7rKqT46JjNnZ2dnUVZ8vGdnZ2d@bt.com> <ju4651$ivo$1@dough.gmane.org> <5005A103.9050802@stoneleaf.us> <mailman.2241.1342549103.4697.python-list@python.org> <Lb-dnVNwAtQOLZjNnZ2dnUVZ7r6dnZ2d@bt.com>
Message-ID <GHnNr.7895$Hs3.4746@fx08.am4> (permalink)
Organization virginmedia.com
Date 2012-07-18 01:46 +0100

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On 17/07/2012 19:36, Lipska the Kat wrote:
> On 17/07/12 19:18, Mark Lawrence wrote:
>> On 17/07/2012 18:29, Ethan Furman wrote:
>>> Terry Reedy wrote:
>>>> On 7/17/2012 10:23 AM, Lipska the Kat wrote:
>>>>
>>>>> Well 'type-bondage' is a strange way of thinking about compile time
>>>>> type
>>>>> checking and making code easier to read (and therefor debug
>>>>
>>>> 'type-bondage' is the requirement to restrict function inputs and
>>>> output to one declared type, where the type declaration mechanisms are
>>>> usually quite limited.
>>>>
>>>> >>> def max(a, b):
>>>> if a <= b: return a
>>>> return b
>>>
>>>
>>> Surely you meant 'if a >= b: . . .'
>>>
>>> No worries, I'm sure your unittests would have caught it. ;)
>>>
>>> ~Ethan~
>>
>> Wouldn't the compiler have caught it before the unittests? :-)
>>
> 
> Not unless the compiler could read your mind!
> The syntax looks fine it's the semantics that are suspect. Wrong is a
> word that I try not to use as it tends to upset people, let's call them
> "differently right" ;-)
> 
> BTW having more than one return statement in a block is a little thing I
> know but it drives me nuts ... another "Pythonic" thing I'll have to get
> used to I suppose.
> 

Its not a pythonic thing.  Its a common and very acceptable paradigm.

Mainly, it avoids complicated breaks from nested control structures, and
especially the 'style' of maintaining one boolean value called
"should_continue" or something equally silly.

My daily work involves C, x86 assembly, reading x86/PCI/ACPI/etc
specifications and cursing violently at some of the stupidity, Python,
Bash and C++, and this is one of the few styles which remains fairly
constant throughout.

Take for example a Linux system call handler.  The general form looks a
little like (substituting C for python style pseudocode)

if not (you are permitted to do this):
    return -EPERM
if not (you've given me some valid data):
    return -EFAULT
if not (you've given me some sensible data):
    return -EINVAL
return actually_try_to_do_something_with(data)

How would you program this sort of logic with a single return statement?
 This is very common logic for all routines for which there is even the
remotest possibility that some data has come from an untrusted source.

~Andrew

P.S. like the sig.

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Thread

Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 09:45 +0100
  Re: Encapsulation, inheritance and polymorphism Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-07-17 06:03 -0400
    Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 12:24 +0100
      Re: Encapsulation, inheritance and polymorphism Larry Hudson <orgnut@yahoo.com> - 2012-07-18 00:10 -0700
  Re: Encapsulation, inheritance and polymorphism Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2012-07-17 11:30 +0200
    Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 12:01 +0100
      Re: Encapsulation, inheritance and polymorphism Dave Angel <d@davea.name> - 2012-07-17 07:23 -0400
      Re: Encapsulation, inheritance and polymorphism Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-17 06:37 -0500
        Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 12:44 +0100
          Re: Encapsulation, inheritance and polymorphism Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-17 06:53 -0500
          Re: Encapsulation, inheritance and polymorphism Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-17 14:35 +0100
        Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 15:01 +0100
          Re: Encapsulation, inheritance and polymorphism Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-17 09:16 -0500
            Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 15:26 +0100
          Re: Encapsulation, inheritance and polymorphism Terry Reedy <tjreedy@udel.edu> - 2012-07-17 13:30 -0400
          Re: Encapsulation, inheritance and polymorphism Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-17 12:57 -0500
      Re: Encapsulation, inheritance and polymorphism Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2012-07-17 14:18 +0200
      Re: Encapsulation, inheritance and polymorphism Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-17 14:29 +0100
      Re: Encapsulation, inheritance and polymorphism Roy Smith <roy@panix.com> - 2012-07-17 09:52 -0400
        Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 15:23 +0100
          Re: Encapsulation, inheritance and polymorphism Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-17 17:26 +0100
            Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 17:46 +0100
          Re: Encapsulation, inheritance and polymorphism Terry Reedy <tjreedy@udel.edu> - 2012-07-17 13:07 -0400
            Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 20:29 +0100
              Re: Encapsulation, inheritance and polymorphism Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-17 20:39 +0100
                Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 20:52 +0100
                Re: Encapsulation, inheritance and polymorphism John Ladasky <john_ladasky@sbcglobal.net> - 2012-08-18 23:05 -0700
                Re: Encapsulation, inheritance and polymorphism John Ladasky <john_ladasky@sbcglobal.net> - 2012-08-18 23:05 -0700
              Re: Encapsulation, inheritance and polymorphism Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-07-17 18:57 -0400
          Re: Encapsulation, inheritance and polymorphism Ethan Furman <ethan@stoneleaf.us> - 2012-07-17 10:29 -0700
          Re: Encapsulation, inheritance and polymorphism Chris Angelico <rosuav@gmail.com> - 2012-07-18 04:01 +1000
          Re: Encapsulation, inheritance and polymorphism Tim Chase <python.list@tim.thechases.com> - 2012-07-17 12:51 -0500
          Re: Encapsulation, inheritance and polymorphism Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-17 19:18 +0100
            Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 19:36 +0100
              Re: Encapsulation, inheritance and polymorphism Andrew Cooper <amc96@cam.ac.uk> - 2012-07-18 01:46 +0100
                Re: Encapsulation, inheritance and polymorphism rusi <rustompmody@gmail.com> - 2012-07-17 20:54 -0700
                Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-18 10:06 +0100
                Re: Encapsulation, inheritance and polymorphism Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2012-07-18 14:01 +0200
                Re: Encapsulation, inheritance and polymorphism "BartC" <bc@freeuk.com> - 2012-07-19 01:41 +0100
                Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-18 13:05 +0000
                Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-18 15:40 +0100
                Re: Encapsulation, inheritance and polymorphism Chris Angelico <rosuav@gmail.com> - 2012-07-19 01:04 +1000
                Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-19 01:22 +0000
                Re: Encapsulation, inheritance and polymorphism Chris Angelico <rosuav@gmail.com> - 2012-07-19 15:09 +1000
                Re: Encapsulation, inheritance and polymorphism Ethan Furman <ethan@stoneleaf.us> - 2012-07-18 08:32 -0700
                Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-18 16:49 +0100
                Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-19 01:34 +0000
                Re: Encapsulation, inheritance and polymorphism rusi <rustompmody@gmail.com> - 2012-07-18 23:09 -0700
                Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-19 09:56 +0100
                Re: Encapsulation, inheritance and polymorphism rusi <rustompmody@gmail.com> - 2012-07-19 08:58 -0700
                Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-19 12:59 +0000
                Re: Encapsulation, inheritance and polymorphism Roy Smith <roy@panix.com> - 2012-07-19 09:06 -0400
                Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-20 07:24 +0000
                Re: Encapsulation, inheritance and polymorphism rusi <rustompmody@gmail.com> - 2012-07-20 01:21 -0700
                Re: Encapsulation, inheritance and polymorphism Paul Rudin <paul.nospam@rudin.co.uk> - 2012-07-19 18:22 +0100
                Re: Encapsulation, inheritance and polymorphism Tim Chase <python.list@tim.thechases.com> - 2012-07-19 13:20 -0500
                Re: Encapsulation, inheritance and polymorphism Chris Angelico <rosuav@gmail.com> - 2012-07-20 04:28 +1000
                Re: Encapsulation, inheritance and polymorphism Tim Chase <python.list@tim.thechases.com> - 2012-07-19 13:50 -0500
                Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-20 08:11 +0000
                Re: Encapsulation, inheritance and polymorphism Erik Max Francis <max@alcyone.com> - 2012-07-20 02:08 -0700
                Re: Encapsulation, inheritance and polymorphism "BartC" <bc@freeuk.com> - 2012-07-20 11:28 +0100
                Re: Encapsulation, inheritance and polymorphism Erik Max Francis <max@alcyone.com> - 2012-07-21 14:32 -0700
                Re: Encapsulation, inheritance and polymorphism Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-23 16:36 +0000
                Re: Encapsulation, inheritance and polymorphism Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-07-19 16:47 -0400
                Re: Encapsulation, inheritance and polymorphism John Gordon <gordon@panix.com> - 2012-07-19 21:01 +0000
                Re: Encapsulation, inheritance and polymorphism Chris Angelico <rosuav@gmail.com> - 2012-07-20 08:20 +1000
                Re: Encapsulation, inheritance and polymorphism John Gordon <gordon@panix.com> - 2012-07-19 22:23 +0000
                Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-20 08:27 +0000
                Re: Encapsulation, inheritance and polymorphism Virgil Stokes <vs@it.uu.se> - 2012-07-20 11:05 +0200
                Re: Encapsulation, inheritance and polymorphism Hans Mulder <hansmu@xs4all.nl> - 2012-07-20 19:45 +0200
                Re: Encapsulation, inheritance and polymorphism Erik Max Francis <max@alcyone.com> - 2012-07-21 14:28 -0700
                Re: Encapsulation, inheritance and polymorphism Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-07-20 13:57 -0400
                Re: Encapsulation, inheritance and polymorphism Ian Kelly <ian.g.kelly@gmail.com> - 2012-07-19 15:13 -0600
                Re: Encapsulation, inheritance and polymorphism Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-07-19 17:30 -0400
                Re: Encapsulation, inheritance and polymorphism Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-20 10:00 +0100
                Re: Encapsulation, inheritance and polymorphism Terry Reedy <tjreedy@udel.edu> - 2012-07-19 02:11 -0400
                Re: Encapsulation, inheritance and polymorphism Albert van der Horst <albert@spenarnc.xs4all.nl> - 2012-07-23 16:18 +0000
                Re: Encapsulation, inheritance and polymorphism Chris Angelico <rosuav@gmail.com> - 2012-07-24 02:15 +1000
                Re: Encapsulation, inheritance and polymorphism Robert Miles <robertmiles@teranews.com> - 2012-08-19 00:21 -0500
                Re: Encapsulation, inheritance and polymorphism Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-19 09:55 +0100
                Re: Encapsulation, inheritance and polymorphism lipska the kat <lipskathekat@yahoo.co.uk> - 2012-08-19 12:50 +0100
                Re: Encapsulation, inheritance and polymorphism Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-08-19 13:06 +0100
          Re: Encapsulation, inheritance and polymorphism Ethan Furman <ethan@stoneleaf.us> - 2012-07-17 11:43 -0700
          Re: Encapsulation, inheritance and polymorphism Devin Jeanpierre <jeanpierreda@gmail.com> - 2012-07-17 15:05 -0400
          Re: Encapsulation, inheritance and polymorphism Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-07-17 20:33 +0100
          Re: Encapsulation, inheritance and polymorphism Ian <hobson42@gmail.com> - 2012-07-17 19:59 +0100
        Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-18 12:58 +0000
          Re: Encapsulation, inheritance and polymorphism Roy Smith <roy@panix.com> - 2012-07-18 09:07 -0400
            Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-18 14:31 +0000
          Re: Encapsulation, inheritance and polymorphism Dave Angel <d@davea.name> - 2012-07-18 12:33 -0400
            Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-19 01:23 +0000
      Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-18 12:43 +0000
      Re: Encapsulation, inheritance and polymorphism Grant Edwards <invalid@invalid.invalid> - 2012-07-18 14:34 +0000
        Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-18 15:48 +0100
          Re: Encapsulation, inheritance and polymorphism Chris Angelico <rosuav@gmail.com> - 2012-07-19 01:09 +1000
            Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-18 16:36 +0100
          Re: Encapsulation, inheritance and polymorphism Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-07-19 01:14 +0000
            Re: Encapsulation, inheritance and polymorphism MRAB <python@mrabarnett.plus.com> - 2012-07-19 02:28 +0100
              Re: Encapsulation, inheritance and polymorphism "OKB (not okblacke)" <brenNOSPAMbarn@NObrenSPAMbarn.net> - 2012-07-19 16:52 +0000
        Re: Encapsulation, inheritance and polymorphism Andrew Berg <bahamutzero8825@gmail.com> - 2012-07-18 10:00 -0500
  Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 13:01 +0100
    Re: Encapsulation, inheritance and polymorphism Terry Reedy <tjreedy@udel.edu> - 2012-07-17 13:24 -0400
      Re: Encapsulation, inheritance and polymorphism Lipska the Kat <lipska@lipskathekat.com> - 2012-07-17 19:21 +0100
    Re: Encapsulation, inheritance and polymorphism MRAB <python@mrabarnett.plus.com> - 2012-07-17 18:43 +0100
    Re: Encapsulation, inheritance and polymorphism Tim Chase <python.list@tim.thechases.com> - 2012-07-17 12:56 -0500
    Re: Encapsulation, inheritance and polymorphism Arnaud Delobelle <arnodel@gmail.com> - 2012-07-18 11:35 +0100

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