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

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From Ned Batchelder <ned@nedbatchelder.com>
Subject Re: An object is an instance (or not)?
Date Tue, 27 Jan 2015 18:22:00 -0500
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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.

> An instance IS an object. On that we can agree. After all, everything in
> Python is an object. Even classes are. We can even pass them as function
> arguments:
>
>      >>> class Sub:
> 	    pass
>
>      >>> def show(aClass):
> 	    print(type(aClass))
> 	
>      >>> show(Sub)
>      <class 'type'>
>
> The problem is that an object isn't always an instance. The word
> instance in OOP has a very formal meaning.

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.

> In programming languages in
> which the classes aren't fully realized objects, it is ok to speak of
> 'instance' and 'object' interchangeably.

I don't know what a "not fully realized object" is.

> But even then, sometimes the
> term 'object instance' is preferred, as a way to separate these
> 'instances' from other variable instances that may not be created from
> class definitions (e.g. C++ built-in types).
>
> The fact that in Python classes are objects, should not just eliminate
> this distinction. The OOP terminology should exist beyond the language
> implementing it. It facilitates discourse and helps transmiting concepts
> when describing your ideas to another programmer. And because in python,
> classes are of the type 'type' and they exist as fully realized objects,
> is no excuse to make a distinction between them and their own fully
> realized instances. The language implementation details should not exist
> as a way for us to freely reformulate long standing terms.
>
> 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?

> 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.

-- 
Ned Batchelder, http://nedbatchelder.com

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Thread

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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