Re: Encapsulation unpythonic?

Date	2013-08-31 08:41 -0400
From	Ned Batchelder <ned@nedbatchelder.com>
Subject	Re: Encapsulation unpythonic?
References	<8255dfbd-a2a1-4ab7-b900-ee19faa459f2@googlegroups.com> <8c7c4854-70e1-46e7-a3ff-a3206c4c5c27@googlegroups.com> <5221567b$0$6599$c3e8da3$5496439d@news.astraweb.com> <ecd32f98-6ba8-4b1e-91d3-e0fd6a8034c3@googlegroups.com> <5221d7ab$0$6599$c3e8da3$5496439d@news.astraweb.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.411.1377952926.19984.python-list@python.org> (permalink)

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On 8/31/13 7:46 AM, Steven D'Aprano wrote:
> On Fri, 30 Aug 2013 23:07:47 -0700, Fabrice Pombet wrote:
>
>> well, look at that:
>>
>> a=(1,2)
>> a=2+3 ->a is an object and I have changed its type and value from
>> outside.
> Incorrect. You have not changed the type or value of any object. "a" is
> not an object, it is a *name*, and while you can change the object bound
> to the name, the objects remain unchanged.
>
> When you do this:
>
> x = 23
> x = 42
>
> the *object* 23 does not change, only the name binding changes. To do
> otherwise would cause all sorts of surprises:
>
> # THIS DOES NOT HAPPEN IN PYTHON
> # or any other language, as far as I am aware
> x = 23
> y = x  # y now has the value 23
> x = 42  # change the value of the object  ### NOT SO! ###
> print y
> => prints 42
>
> Name binding (assignment) does not change objects. It changes the link
> between a name and the object, but the object remains untouched (unless
> it is unbound, and garbage collected). Assignment is not mutation.
> Assigning to a name does not modify the object that was previously bound.
>

I wrote a piece about names and values that might help clarify these 
points: Facts and Myths about Names and Values in Python: 
http://nedbatchelder.com/text/names.html

--Ned.

Thread

Encapsulation unpythonic? fsaldan1@gmail.com - 2013-08-17 05:26 -0700
  Re: Encapsulation unpythonic? Skip Montanaro <skip@pobox.com> - 2013-08-17 07:54 -0500
  Re: Encapsulation unpythonic? David <bouncingcats@gmail.com> - 2013-08-17 23:05 +1000
  Re: Encapsulation unpythonic? Chris Angelico <rosuav@gmail.com> - 2013-08-17 16:50 +0100
  Re: Encapsulation unpythonic? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-17 16:17 +0000
    Re: Encapsulation unpythonic? Joshua Landau <joshua@landau.ws> - 2013-08-18 18:15 +0100
      Re: Encapsulation unpythonic? Steven D'Aprano <steve@pearwood.info> - 2013-08-19 07:05 +0000
        Re: Encapsulation unpythonic? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-08-19 18:57 -0400
        Re: Encapsulation unpythonic? random832@fastmail.us - 2013-08-21 12:52 -0400
          Re: Encapsulation unpythonic? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-22 02:06 +0000
        Re: Encapsulation unpythonic? Ian Kelly <ian.g.kelly@gmail.com> - 2013-08-21 16:02 -0600
  Re: Encapsulation unpythonic? Gary Herron <gary.herron@islandtraining.com> - 2013-08-17 13:16 -0700
  Re: Encapsulation unpythonic? Terry Reedy <tjreedy@udel.edu> - 2013-08-17 17:22 -0400
  Re: Encapsulation unpythonic? Chris Angelico <rosuav@gmail.com> - 2013-08-18 01:59 +0100
  Re: Encapsulation unpythonic? chaz2cry@gmail.com - 2013-08-22 19:12 -0700
  Re: Encapsulation unpythonic? Fabrice Pombet <fp2161@gmail.com> - 2013-08-30 10:43 -0700
    Re: Encapsulation unpythonic? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-31 02:35 +0000
      Re: Encapsulation unpythonic? Fabrice Pombet <fp2161@gmail.com> - 2013-08-30 23:07 -0700
        Re: Encapsulation unpythonic? Marco Buttu <marco.buttu@gmail.com> - 2013-08-31 08:49 +0200
        Re: Encapsulation unpythonic? Gary Herron <gherron@digipen.edu> - 2013-08-31 00:03 -0700
          Re: Encapsulation unpythonic? Fabrice Pombet <fp2161@gmail.com> - 2013-08-31 00:42 -0700
            Re: Encapsulation unpythonic? Fabrice Pombet <fp2161@gmail.com> - 2013-08-31 01:00 -0700
        Re: Encapsulation unpythonic? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-08-31 11:46 +0000
          Re: Encapsulation unpythonic? Ned Batchelder <ned@nedbatchelder.com> - 2013-08-31 08:41 -0400
            Re: Encapsulation unpythonic? Fabrice Pombet <fp2161@gmail.com> - 2013-08-31 05:49 -0700
          Re: Encapsulation unpythonic? Fabrice Pombet <fp2161@gmail.com> - 2013-08-31 05:57 -0700
            Re: Encapsulation unpythonic? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-09-01 08:10 +0000
              Re: Encapsulation unpythonic? Chris Angelico <rosuav@gmail.com> - 2013-09-01 18:21 +1000
                Re: Encapsulation unpythonic? Fabrice Pombet <fp2161@gmail.com> - 2013-09-01 03:09 -0700
                Re: Encapsulation unpythonic? Ethan Furman <ethan@stoneleaf.us> - 2013-09-01 11:42 -0700
                Re: Encapsulation unpythonic? Roy Smith <roy@panix.com> - 2013-09-01 15:13 -0400
                Re: Encapsulation unpythonic? Ethan Furman <ethan@stoneleaf.us> - 2013-09-01 13:33 -0700
                Re: Encapsulation unpythonic? Tim Delaney <timothy.c.delaney@gmail.com> - 2013-09-02 07:54 +1000
                Re: Encapsulation unpythonic? Roy Smith <roy@panix.com> - 2013-09-01 18:02 -0400
                Re: Encapsulation unpythonic? Ethan Furman <ethan@stoneleaf.us> - 2013-09-01 17:24 -0700
                Re: Encapsulation unpythonic? Roy Smith <roy@panix.com> - 2013-09-01 20:59 -0400
                Re: Encapsulation unpythonic? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-09-02 02:57 +0000
                Re: Encapsulation unpythonic? Ethan Furman <ethan@stoneleaf.us> - 2013-09-01 21:15 -0700
                Re: Encapsulation unpythonic? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-09-02 01:57 +0000
              Re: Encapsulation unpythonic? Ben Finney <ben+python@benfinney.id.au> - 2013-09-02 09:32 +1000
                Re: Encapsulation unpythonic? Roy Smith <roy@panix.com> - 2013-09-01 20:52 -0400
          Re: Encapsulation unpythonic? "Rhodri James" <rhodri@wildebst.demon.co.uk> - 2013-09-03 00:29 +0100
            Re: Encapsulation unpythonic? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-09-03 22:41 -0400
        Re: Encapsulation unpythonic? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-08-31 13:31 -0400
        Re: Encapsulation unpythonic? Tim Delaney <timothy.c.delaney@gmail.com> - 2013-09-01 03:47 +1000
    Re: Encapsulation unpythonic? 88888 Dihedral <dihedral88888@gmail.com> - 2013-09-02 14:43 -0700

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