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Re: Terminology: “reference” versus “pointer”

From Ben Finney <ben+python@benfinney.id.au>
Subject Re: Terminology: “reference” versus “pointer”
Date 2015-09-12 14:52 +1000
References (4 earlier) <1442016698.95299.381478313.2487CA0E@webmail.messagingengine.com> <mt04ao$ite$1@ger.gmane.org> <m2zj0ss2md.fsf@fastmail.com> <85mvws6z45.fsf_-_@benfinney.id.au> <m2k2rws0yr.fsf@fastmail.com>
Newsgroups comp.lang.python
Message-ID <mailman.406.1442033578.8327.python-list@python.org> (permalink)

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Random832 <random832@fastmail.com> writes:

> Ben Finney <ben+python@benfinney.id.au> writes:
> > With the significant difference that “pointer” implies that it has its
> > own value accessible directly by the running program, such as a pointer
> > in C.
>
> Its own value *is* what you're accessing when you assign or return it.

You're not describing Python references. But I don't know what you are
describing with all those “it”s — what language, what behaviour, what
concept?

Can you clarify what you mean, and what in my description you are
disagreeing with?

> > That's different from a “reference”, which to my understanding
> > implies the running program does *not* normally have direct access
> > to it as a distinct value. The only way you can use a reference is
> > to get at the object to which it refers.
>
> In C++, references cannot be reassigned. I consider *that* the
> fundamental difference - a pointer is a variable that you can reassign
> and return; a reference always refers to the same object once created.

Sure, that will work fine.

So in Python, we don't have pointers because we don't have access to
change or reassign them.

A Python reference isn't accessible and can't be changed; you can just
make another reference and switch to that.

You can't, for example, keep the old reference (there are no references
to references in Python), because they're not accessible as values in
themselves. Once you assign a different reference, the old one is gone
and can't be found again.

-- 
 \            “[T]he great menace to progress is not ignorance but the |
  `\           illusion of knowledge.” —Daniel J. Boorstin, historian, |
_o__)                                                        1914–2004 |
Ben Finney

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Re: Python handles globals badly. tdev@freenet.de - 2015-09-11 14:26 -0700
  Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-11 23:50 +0200
    Re: Python handles globals badly. Michael Torrie <torriem@gmail.com> - 2015-09-11 18:01 -0600
      Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-12 07:22 +0200
        Re: Python handles globals badly. MRAB <python@mrabarnett.plus.com> - 2015-09-12 18:05 +0100
          Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-13 14:04 +0200
            Re: Python handles globals badly. Steven D'Aprano <steve@pearwood.info> - 2015-09-13 22:06 +1000
              Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-13 14:11 +0200
                Re: Python handles globals badly. Ned Batchelder <ned@nedbatchelder.com> - 2015-09-13 05:17 -0700
                Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-15 05:36 +0200
        Re: Python handles globals badly. Emile van Sebille <emile@fenx.com> - 2015-09-12 10:18 -0700
          Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-13 14:06 +0200
            Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-13 14:10 +0200
        Re: Python handles globals badly. Michael Torrie <torriem@gmail.com> - 2015-09-12 20:32 -0600
          Re: Python handles globals badly. "Skybuck Flying" <skybuck2000@hotmail.com> - 2015-09-13 14:05 +0200
    Re: Python handles globals badly. random832@fastmail.us - 2015-09-11 20:11 -0400
    Re: Python handles globals badly. Michael Torrie <torriem@gmail.com> - 2015-09-11 18:34 -0600
    Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 03:57 +0100
    Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 04:01 +0100
    Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 00:06 -0400
    Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 00:16 -0400
    Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 05:17 +0100
    Terminology: “reference” versus “pointer” (was: Python handles globals badly.) Ben Finney <ben+python@benfinney.id.au> - 2015-09-12 14:27 +1000
    Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 05:34 +0100
    Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 00:34 -0400
    Re: Terminology: “reference” versus “pointer” Random832 <random832@fastmail.com> - 2015-09-12 00:42 -0400
      Re: Terminology: “reference” versus “pointer” Steven D'Aprano <steve@pearwood.info> - 2015-09-13 02:32 +1000
        Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 09:54 -0700
          Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-13 03:06 +1000
          Re: Terminology: "reference" versus "pointer" Emile van Sebille <emile@fenx.com> - 2015-09-12 10:14 -0700
          Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 03:24 +1000
            Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-13 03:34 +1000
    Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 05:45 +0100
    Re: Terminology: “reference” versus “pointer” Ben Finney <ben+python@benfinney.id.au> - 2015-09-12 14:52 +1000
    Re: Terminology: “reference” versus “pointer” Random832 <random832@fastmail.com> - 2015-09-12 01:03 -0400
      Re: Terminology: “reference” versus “pointer” Steven D'Aprano <steve@pearwood.info> - 2015-09-13 02:50 +1000
        Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 10:04 -0700
    Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 01:07 -0400
    Re: Terminology: “reference” versus “pointer” Ben Finney <ben+python@benfinney.id.au> - 2015-09-12 15:20 +1000
    Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 06:25 +0100
    Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 01:35 -0400
    Re: Terminology: “reference” versus “pointer” Random832 <random832@fastmail.com> - 2015-09-12 01:42 -0400
    Re: Python handles globals badly. Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 06:54 +0100
    Re: Terminology: “reference” versus “pointer” Chris Angelico <rosuav@gmail.com> - 2015-09-12 16:02 +1000
    Re: Terminology: “reference” versus “pointer” Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-12 07:05 +0100
    Re: Python handles globals badly. Chris Angelico <rosuav@gmail.com> - 2015-09-12 16:13 +1000
    Re: Terminology: “reference” versus “pointer” Random832 <random832@fastmail.com> - 2015-09-12 02:15 -0400
    Re: Python handles globals badly. Random832 <random832@fastmail.com> - 2015-09-12 02:25 -0400
    Re: Terminology: “reference” versus “pointer” Ben Finney <ben+python@benfinney.id.au> - 2015-09-12 16:26 +1000
      Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 05:46 -0700
        Re: Terminology: "reference" versus "pointer" Laura Creighton <lac@openend.se> - 2015-09-12 16:41 +0200
          Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 08:13 -0700
            Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 09:17 -0700
              Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 10:12 -0700
                Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 04:14 +1000
              Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 03:48 +1000
                Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 11:45 -0700
                Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 22:50 +1000
                Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 23:29 +1000
                Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-13 18:34 -0700
                Re: Terminology: "reference" versus "pointer" Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-14 04:34 +0100
                Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 12:58 -0700
                Re: Terminology: "reference" versus "pointer" Emile van Sebille <emile@fenx.com> - 2015-09-12 15:14 -0700
                Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 15:34 -0700
                Re: Terminology: "reference" versus "pointer" Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-13 00:14 +0100
                Re: Terminology: "reference" versus "pointer" Ned Batchelder <ned@nedbatchelder.com> - 2015-09-12 17:02 -0700
                Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 17:28 -0700
                Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 17:44 -0700
                Re: Terminology: "reference" versus "pointer" Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-09-13 03:22 +0100
                Re: Terminology: "reference" versus "pointer" Ned Batchelder <ned@nedbatchelder.com> - 2015-09-12 19:25 -0700
                Re: Terminology: "reference" versus "pointer" Michael Torrie <torriem@gmail.com> - 2015-09-12 20:35 -0600
                Re: Terminology: "reference" versus "pointer" Ben Finney <ben+python@benfinney.id.au> - 2015-09-13 12:42 +1000
                Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-13 08:31 -0700
                Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-14 01:39 +1000
                Re: Terminology: "reference" versus "pointer" Ben Finney <ben+python@benfinney.id.au> - 2015-09-14 06:48 +1000
                Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-13 18:13 -0700
                Re: Terminology: "reference" versus "pointer" Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-09-13 12:32 -0400
                Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 17:23 -0700
                Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 16:39 -0700
                Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-13 10:19 +1000
                Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 17:25 -0700
                Re: Terminology: "reference" versus "pointer" rurpy@yahoo.com - 2015-09-12 18:07 -0700
            Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-12 20:54 +0300
              Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 11:21 -0700
                Re: Terminology: "reference" versus "pointer" Jussi Piitulainen <harvesting@makes.email.invalid> - 2015-09-12 23:02 +0300
                Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-12 17:10 -0400
                Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 12:30 +1000
                Re: Terminology: "reference" versus "pointer" Jussi Piitulainen <harvesting@makes.email.invalid> - 2015-09-13 09:40 +0300
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-12 23:13 +0300
                Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-12 17:27 -0400
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-13 21:04 +0300
                Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-14 05:03 +1000
                Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-13 15:04 -0400
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 02:17 +0300
                Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-14 11:10 +1000
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 04:22 +0300
                Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-14 12:38 +1000
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 06:23 +0300
                Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-15 02:59 +1000
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 20:24 +0300
                Re: Terminology: "reference" versus "pointer" Ned Batchelder <ned@nedbatchelder.com> - 2015-09-14 11:29 -0700
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 22:30 +0300
                Re: Terminology: "reference" versus "pointer" Ned Batchelder <ned@nedbatchelder.com> - 2015-09-14 13:16 -0700
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 23:32 +0300
                Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-14 11:30 +1000
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 05:26 +0300
                Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-14 09:52 +1000
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 03:30 +0300
                Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-14 10:58 +1000
                Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-13 19:38 -0400
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 17:48 +0300
                Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-14 11:10 -0400
                Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-15 03:03 +1000
                Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-14 13:34 -0400
                Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-16 00:26 +1000
                Re: Terminology: "reference" versus "pointer" Emile van Sebille <emile@fenx.com> - 2015-09-14 10:51 -0700
                Re: Terminology: "reference" versus "pointer" Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-09-16 20:14 +1200
                Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-16 18:18 +1000
                Re: Terminology: "reference" versus "pointer" Ben Finney <ben+python@benfinney.id.au> - 2015-09-16 18:24 +1000
                Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-16 18:33 +1000
                Re: Terminology: "reference" versus "pointer" Chris Angelico <rosuav@gmail.com> - 2015-09-15 03:59 +1000
                Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-14 14:02 -0400
                Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-16 00:14 +1000
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 20:45 +0300
                Re: Terminology: "reference" versus "pointer" Random832 <random832@fastmail.com> - 2015-09-14 14:00 -0400
                Re: Terminology: "reference" versus "pointer" Akira Li <4kir4.1i@gmail.com> - 2015-09-14 21:17 +0300
        Re: Terminology: "reference" versus "pointer" Steven D'Aprano <steve@pearwood.info> - 2015-09-13 03:08 +1000
          Re: Terminology: "reference" versus "pointer" Rustom Mody <rustompmody@gmail.com> - 2015-09-12 10:26 -0700
        Re: Terminology: "reference" versus "pointer" Ben Finney <ben+python@benfinney.id.au> - 2015-09-13 11:13 +1000
    Re: Python handles globals badly. Chris Angelico <rosuav@gmail.com> - 2015-09-12 16:27 +1000
    Re: Terminology: “reference” versus “pointer” Chris Angelico <rosuav@gmail.com> - 2015-09-12 16:31 +1000
  Re: Python handles globals badly. Ian Kelly <ian.g.kelly@gmail.com> - 2015-09-11 16:10 -0600
  Re: Python handles globals badly. MRAB <python@mrabarnett.plus.com> - 2015-09-12 00:03 +0100

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