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Re: An object is an instance (or not)?

From Ben Finney <ben+python@benfinney.id.au>
Subject Re: An object is an instance (or not)?
Date 2015-01-28 10:39 +1100
References <MPG.2f320f923eedd5a69896a1@nntp.aioe.org> <ma96io$ovh$1@ger.gmane.org>
Newsgroups comp.lang.python
Message-ID <mailman.18192.1422401989.18130.python-list@python.org> (permalink)

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Ned Batchelder <ned@nedbatchelder.com> writes:

> On 1/27/15 3:12 PM, Mario Figueiredo wrote:
> > This is a follow up from a previous discussion in which it is argued
> > that the following code produces the correct error message terminology,
> > considering that in Python an object is also an instance.
>
> I don't know what the difference is between "object" and "instance".
> An object is an instance of a class.  The two words are
> interchangeable as far as I know.

Not in English grammar, IMO. To say “foo is an instance” implies the
sentence isn't finished; the term “instance” only makes sense in the
context of a relationship to some class. To say “foo is an object”
doesn't have that implication.

> A common mistake is to believe that "OOP" is a well-defined term.
> It's not it's a collection of ideas that are expressed slightly
> differently in each language.

Right. The common meaning of “object” shared by all OOP systems is
surprisingly small.

Many OOP systems do not use classes (e.g. JavaScript) and are no less
object-oriented for that. In such a system it would be true to say “foo
is an object, but is not an instance of anything”.

> > Because, from my own study of Python, I've came to realize that the
> > distinction between objects and instances of objects actually
> > exists. In Python, class objects cannot participate in OOP, only
> > their instances.
>
> What does "participate in OOP" mean?

To the extent I understand (and I'm confused on what that might mean as
you are), I think it's plainly false.

In Python, every class is an object. Every class has the full range of
behaviour that we expect of objects. A class just has the additional
feature that it can be instantiated.

> > This is why I say that even in Python, where a class is an object,
> > an object is not always an instance. The language itself forces that
> > distinction.

You have not, to my knowledge, shown any object (in Python 2.2 or later)
which is not an instance of some class. Python objects are always an
instance of some specific class.

-- 
 \     “Books and opinions, no matter from whom they came, if they are |
  `\     in opposition to human rights, are nothing but dead letters.” |
_o__)                                                  —Ernestine Rose |
Ben Finney

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An object is an instance (or not)? Mario Figueiredo <marfig@gmail.com> - 2015-01-27 21:12 +0100
  Re: An object is an instance (or not)? Ethan Furman <ethan@stoneleaf.us> - 2015-01-27 12:36 -0800
  Re: An object is an instance (or not)? André Roberge <andre.roberge@gmail.com> - 2015-01-27 12:50 -0800
    Re: An object is an instance (or not)? Mario Figueiredo <marfig@gmail.com> - 2015-01-27 22:06 +0100
      Re: An object is an instance (or not)? André Roberge <andre.roberge@gmail.com> - 2015-01-27 13:38 -0800
        Re: An object is an instance (or not)? Mario Figueiredo <marfig@gmail.com> - 2015-01-27 22:43 +0100
          Re: An object is an instance (or not)? André Roberge <andre.roberge@gmail.com> - 2015-01-27 13:49 -0800
            Re: An object is an instance (or not)? Mario Figueiredo <marfig@gmail.com> - 2015-01-27 22:58 +0100
              Re: An object is an instance (or not)? Ben Finney <ben+python@benfinney.id.au> - 2015-01-28 09:32 +1100
                Re: An object is an instance (or not)? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-28 18:55 +1100
                Re: An object is an instance (or not)? Ben Finney <ben+python@benfinney.id.au> - 2015-01-28 22:20 +1100
              Re: An object is an instance (or not)? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-01-27 23:12 +0000
                Re: An object is an instance (or not)? Mario Figueiredo <marfig@gmail.com> - 2015-01-28 01:52 +0100
                Re: An object is an instance (or not)? Marko Rauhamaa <marko@pacujo.net> - 2015-01-28 07:25 +0200
                Re: An object is an instance (or not)? Rustom Mody <rustompmody@gmail.com> - 2015-01-27 21:53 -0800
                Re: An object is an instance (or not)? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-01-28 05:57 +0000
                Re: An object is an instance (or not)? Mario Figueiredo <marfig@gmail.com> - 2015-01-28 11:48 +0100
      Re: An object is an instance (or not)? random832@fastmail.us - 2015-01-28 00:37 -0500
        Re: An object is an instance (or not)? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-28 19:45 +1100
      Re: An object is an instance (or not)? Devin Jeanpierre <jeanpierreda@gmail.com> - 2015-01-27 21:43 -0800
      Re: An object is an instance (or not)? random832@fastmail.us - 2015-01-28 01:01 -0500
        Re: An object is an instance (or not)? Rustom Mody <rustompmody@gmail.com> - 2015-01-27 22:22 -0800
          Re: An object is an instance (or not)? Ben Finney <ben+python@benfinney.id.au> - 2015-01-28 18:03 +1100
        Re: An object is an instance (or not)? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-28 19:48 +1100
      Re: An object is an instance (or not)? Ben Finney <ben+python@benfinney.id.au> - 2015-01-28 17:59 +1100
      Re: An object is an instance (or not)? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-01-28 20:21 +1300
      Re: An object is an instance (or not)? Ben Finney <ben+python@benfinney.id.au> - 2015-01-28 18:48 +1100
      Re: An object is an instance (or not)? random832@fastmail.us - 2015-01-28 12:08 -0500
        Re: An object is an instance (or not)? Rustom Mody <rustompmody@gmail.com> - 2015-01-28 18:29 -0800
  Re: An object is an instance (or not)? Ned Batchelder <ned@nedbatchelder.com> - 2015-01-27 18:22 -0500
    Re: An object is an instance (or not)? Mario Figueiredo <marfig@gmail.com> - 2015-01-28 01:17 +0100
      Re: An object is an instance (or not)? Chris Angelico <rosuav@gmail.com> - 2015-01-28 11:30 +1100
        Re: An object is an instance (or not)? Mario Figueiredo <marfig@gmail.com> - 2015-01-28 01:35 +0100
          Re: An object is an instance (or not)? alex23 <wuwei23@gmail.com> - 2015-01-28 14:44 +1000
          Re: An object is an instance (or not)? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-01-28 23:33 +1300
            Re: An object is an instance (or not)? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-28 22:52 +1100
              Re: An object is an instance (or not)? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-01-29 19:22 +1300
                Re: An object is an instance (or not)? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-29 18:16 +1100
                Re: An object is an instance (or not)? Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-29 08:48 -0700
                Re: An object is an instance (or not)? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-01-30 22:07 +1300
                Re: An object is an instance (or not)? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-31 10:45 +1100
      Re: An object is an instance (or not)? Ned Batchelder <ned@nedbatchelder.com> - 2015-01-27 21:21 -0500
        Re: An object is an instance (or not)? Rustom Mody <rustompmody@gmail.com> - 2015-01-27 18:52 -0800
        Re: An object is an instance (or not)? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-28 20:16 +1100
          Re: An object is an instance (or not)? Chris Angelico <rosuav@gmail.com> - 2015-01-28 21:01 +1100
            Re: An object is an instance (or not)? Rick Johnson <rantingrickjohnson@gmail.com> - 2015-01-29 14:22 -0800
      Re: An object is an instance (or not)? Ian Kelly <ian.g.kelly@gmail.com> - 2015-01-27 19:15 -0700
      Re: An object is an instance (or not)? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-28 20:28 +1100
      Re: An object is an instance (or not)? Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-01-28 23:33 +1300
    Re: An object is an instance (or not)? Grant Edwards <invalid@invalid.invalid> - 2015-01-28 00:23 +0000
  Re: An object is an instance (or not)? Ben Finney <ben+python@benfinney.id.au> - 2015-01-28 10:39 +1100
    Re: An object is an instance (or not)? Mario Figueiredo <marfig@gmail.com> - 2015-01-28 01:24 +0100
      Re: An object is an instance (or not)? Ben Finney <ben+python@benfinney.id.au> - 2015-01-28 12:00 +1100
        Re: An object is an instance (or not)? Mario Figueiredo <marfig@gmail.com> - 2015-01-28 02:14 +0100
      Re: An object is an instance (or not)? alex23 <wuwei23@gmail.com> - 2015-01-28 14:47 +1000
        Re: An object is an instance (or not)? Rustom Mody <rustompmody@gmail.com> - 2015-01-27 21:23 -0800
        Re: An object is an instance (or not)? random832@fastmail.us - 2015-01-28 00:44 -0500
          Re: An object is an instance (or not)? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-28 20:21 +1100
      Re: An object is an instance (or not)? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-28 20:17 +1100
    Re: An object is an instance (or not)? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-01-28 20:09 +1100
  Re: An object is an instance (or not)? Chris Angelico <rosuav@gmail.com> - 2015-01-28 10:42 +1100
    Re: An object is an instance (or not)? Mario Figueiredo <marfig@gmail.com> - 2015-01-28 01:31 +0100
  Re: An object is an instance (or not)? Rustom Mody <rustompmody@gmail.com> - 2015-01-27 18:11 -0800

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