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Re: Classes

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Date Tue, 4 Nov 2014 02:34:30 +1100
Subject Re: Classes
From Chris Angelico <rosuav@gmail.com>
Cc "python-list@python.org" <python-list@python.org>
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On Tue, Nov 4, 2014 at 12:50 AM, Dennis Lee Bieber
<wlfraed@ix.netcom.com> wrote:
> On Mon, 3 Nov 2014 03:12:32 +0000 (UTC), Denis McMahon
> <denismfmcmahon@gmail.com> declaimed the following:
>
>>So:
>>
>>Quadrilateral
>>    Parallelogram
>>        Square
>>        Rectangle
>>        Rhombus
>>        Diamond (4 sides eq)
>>    Trapezoid
>>        Arrowhead
>>
>>Is an arrowhead a trapezoid?
>
>         I'd probably indent square under rectangle, and indent diamond where it
> is -- both being restrictions on rectangle/rhombus
>
>         But we may need another category, convex and concave; the arrowhead
> would fall into the concave grouping.

That's fine if you're creating a taxonomical hierarchy of immutables,
but neither works if you're creating a mutable class hierarchy that
follows LSP. The only way you can make any of this work (as someone
suggested earlier, I believe) is by having __new__ potentially return
a subclass, so if you ask Parallelogram to give you one with all sides
equal and all angles equal, it gives you back a Square. But since a
square is a special form of rhombus as well as a special form of
rectangle, you'd have to use multiple inheritance or an AST-style
subclass hook to verify. Of course, if you're going down that route,
you probably want to take this up a level and have a Shape class, and
have the subclass hook simply check if it's four-sided as well.

ChrisA

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Classes   Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-30 16:16 -0400
  Re: Classes sohcahtoa82@gmail.com - 2014-10-30 13:33 -0700
    Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-30 17:00 -0400
  Re: Classes Rob Gaddi <rgaddi@technologyhighland.invalid> - 2014-10-30 13:34 -0700
    Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-30 17:00 -0400
  Re: Classes Larry Hudson <orgnut@yahoo.com> - 2014-10-30 14:28 -0700
    Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-30 17:34 -0400
      Re: Classes sohcahtoa82@gmail.com - 2014-10-30 18:21 -0700
      Re: Classes alister <alister.nospam.ware@ntlworld.com> - 2014-10-31 09:59 +0000
        Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 10:07 -0400
  Re: Classes   "ast" <nomail@invalid.com> - 2014-10-31 10:05 +0100
    Re: Classes   "ast" <nomail@invalid.com> - 2014-10-31 10:18 +0100
      Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-10-31 20:21 +1100
    Re: Classes   Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 10:05 -0400
      Re: Classes Ian Kelly <ian.g.kelly@gmail.com> - 2014-10-31 08:47 -0600
        Re: Classes Grant Edwards <invalid@invalid.invalid> - 2014-10-31 15:49 +0000
          Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 12:31 -0400
            Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 03:37 +1100
              Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 12:47 -0400
                Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 04:02 +1100
                Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 13:31 -0400
                Re: Classes Zachary Ware <zachary.ware+pylist@gmail.com> - 2014-10-31 12:39 -0500
                Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 13:57 -0400
                Re: Classes Rob Gaddi <rgaddi@technologyhighland.invalid> - 2014-10-31 10:40 -0700
                Re: Classes Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-11-01 11:17 +1300
                Re: Classes Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-01 12:06 +1100
                Re: Classes Ian Kelly <ian.g.kelly@gmail.com> - 2014-11-01 00:12 -0600
                Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 17:32 +1100
                Re: Classes Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-11-03 00:32 +1300
            Re: Classes Dave Angel <davea@davea.name> - 2014-10-31 13:20 -0400
            Re: Classes Marko Rauhamaa <marko@pacujo.net> - 2014-10-31 19:35 +0200
            Re: Classes Grant Edwards <invalid@invalid.invalid> - 2014-10-31 17:40 +0000
            Re: Classes Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-10-31 18:26 -0400
              Re: Classes Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-01 12:09 +1100
      Re: Classes   Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-11-01 04:06 +1100
        Re: Classes   Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 13:18 -0400
          Re: Classes Rob Gaddi <rgaddi@technologyhighland.invalid> - 2014-10-31 10:43 -0700
            Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 14:18 -0400
              Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 14:42 -0400
              Re: Classes Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-10-31 18:57 -0400
                Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 19:22 -0400
                Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 19:32 -0400
                Re: Classes Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-11-01 12:00 -0400
                Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-11-01 12:42 -0400
                Re: Classes Denis McMahon <denismfmcmahon@gmail.com> - 2014-11-02 09:50 +0000
                Re: Classes Tim Delaney <timothy.c.delaney@gmail.com> - 2014-11-02 21:32 +1100
                Re: Classes Denis McMahon <denismfmcmahon@gmail.com> - 2014-11-02 12:27 +0000
                Re: Classes Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-11-02 11:31 -0500
                Re: Classes Denis McMahon <denismfmcmahon@gmail.com> - 2014-11-03 03:12 +0000
                Re: Classes Dan Sommers <dan@tombstonezero.net> - 2014-11-03 06:29 +0000
                Re: Classes Denis McMahon <denismfmcmahon@gmail.com> - 2014-11-04 01:10 +0000
                Re: Classes Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2014-11-04 18:30 +1300
                Re: Classes Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2014-11-03 08:50 -0500
                Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-04 02:34 +1100
                Re: Classes Ian Kelly <ian.g.kelly@gmail.com> - 2014-11-03 07:47 -0700
                Re: Classes Larry Hudson <orgnut@yahoo.com> - 2014-11-02 14:03 -0800
            Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 07:51 +1100
              Re: Classes sohcahtoa82@gmail.com - 2014-10-31 14:24 -0700
                Re: Classes Rob Gaddi <rgaddi@technologyhighland.invalid> - 2014-10-31 14:40 -0700
                Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 08:56 +1100
                Re: Classes Chris Angelico <rosuav@gmail.com> - 2014-11-01 08:36 +1100
          Re: Classes Grant Edwards <invalid@invalid.invalid> - 2014-10-31 17:43 +0000
    Re: Classes Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-10-31 14:11 +0000
    Re: Classes   Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 12:49 -0400
      Re: Classes   "ast" <nomail@invalid.com> - 2014-10-31 19:31 +0100
        Re: Classes   Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 14:36 -0400
        Re: Classes Joel Goldstick <joel.goldstick@gmail.com> - 2014-10-31 14:41 -0400
          Re: Classes Seymore4Head <Seymore4Head@Hotmail.invalid> - 2014-10-31 14:56 -0400

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