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Re: Reference

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Date Wed, 5 Mar 2014 12:12:54 -0600
From Tim Chase <python.list@tim.thechases.com>
To Rustom Mody <rustompmody@gmail.com>
Subject Re: Reference
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Xref csiph.com comp.lang.python:67865

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On 2014-03-05 09:40, Rustom Mody wrote:
> Every object has an identity, a type and a value. An object's
> identity never changes once it has been created; you may think of
> it as the object's address in memory. The 'is' operator compares
> the identity of two objects; the id() function returns an integer
> representing its identity (currently implemented as its address).
> 
> from http://docs.python.org/2/reference/datamodel.html

Note the "currently", which does not mean "now, always, and forever
for every implementation".

From http://docs.python.org/3/library/functions.html#id

"""
    Return the “identity” of an object. This is an integer which is
    guaranteed to be unique and constant for this object during its
    lifetime. Two objects with non-overlapping lifetimes may have the
    same id() value.

    CPython implementation detail: This is the address of the object
    in memory.
"""

This is clearly documented as a *CPython implementation detail*.  The
id() function is free to return sequential integers, arbitrary
integers, memory addresses, GUIDs-as-integers, or hashes-as-integers
for some internal representation.

The only thing that matters is (1) that id() returns *some* integer
identifying the object, and (2) the ability to compare id(thing1) with
id(thing2) and see if they are the same or different (assuming thing1
and thing2 share lifetimes during their id() calls), regardless of
what is actually returned.

> So when you say
> > I'll re-iterate that "memory location of the object" isn't a valid
> > response. 
> 
> well... all I can say is I dont know what to say :-)

That you live in a CPython world, unencumbered by experience in other
flavors of language-spec-compliant Python interpreters where id()
returns integers that *aren't* memory addresses?

-tkc

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Thread

Reference "ast" <nomail@invalid.com> - 2014-03-03 10:42 +0100
  Object identity (was: Reference) Ben Finney <ben+python@benfinney.id.au> - 2014-03-03 21:00 +1100
    Re: Object identity (was: Reference) "ast" <nomail@invalid.com> - 2014-03-03 11:21 +0100
  Re: Reference "Mark H. Harris" <harrismh777@gmail.com> - 2014-03-03 05:09 -0800
  Re: Reference Grant Edwards <invalid@invalid.invalid> - 2014-03-03 14:29 +0000
  Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-03 07:52 -0800
    Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 08:10 +1100
    Re: Reference Tim Chase <python.list@tim.thechases.com> - 2014-03-03 15:24 -0600
    Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 08:31 +1100
    Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-03 21:35 +0000
      Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-04 00:07 +0200
        Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 09:18 +1100
          Re: Reference Alister <alister.ware@ntlworld.com> - 2014-03-04 11:10 +0000
            Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-04 11:48 +0000
              Re: Reference "Rhodri James" <rhodri@wildebst.org.uk> - 2014-03-05 00:25 +0000
    Re: Reference Tim Chase <python.list@tim.thechases.com> - 2014-03-03 15:51 -0600
    Re: Reference Jerry Hill <malaclypse2@gmail.com> - 2014-03-03 17:02 -0500
      Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-04 00:22 +0200
        Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-04 09:27 +1100
        Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 09:33 +1100
        Re: Reference Steven D'Aprano <steve@pearwood.info> - 2014-03-04 04:52 +0000
          Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-04 16:24 +1100
            Re: Reference "Rhodri James" <rhodri@wildebst.org.uk> - 2014-03-05 01:08 +0000
              Re: Reference Roy Smith <roy@panix.com> - 2014-03-04 21:09 -0500
                Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 19:36 -0800
                Re: Reference Ian Kelly <ian.g.kelly@gmail.com> - 2014-03-04 21:08 -0700
                Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 20:31 -0800
                Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-05 15:32 +1100
                Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 20:47 -0800
                Re: Reference Steven D'Aprano <steve@pearwood.info> - 2014-03-05 05:06 +0000
                Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 21:47 -0800
                Re: Reference alex23 <wuwei23@gmail.com> - 2014-03-05 16:01 +1000
                Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 22:10 -0800
                Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-05 17:22 +1100
                Re: Reference alex23 <wuwei23@gmail.com> - 2014-03-05 16:28 +1000
                Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-05 12:24 +0000
                Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-05 12:21 +0000
                Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-05 17:20 +1100
                Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-05 09:40 -0800
                Re: Reference Tim Chase <python.list@tim.thechases.com> - 2014-03-05 12:12 -0600
                Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 05:33 +1100
                Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-05 18:19 +0000
                Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 22:23 +0200
                Re: Reference Grant Edwards <invalid@invalid.invalid> - 2014-03-05 20:31 +0000
                Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 22:46 +0200
                Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 08:07 +1100
                Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 08:10 +1100
                Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-05 21:34 +0000
                Re: Reference Terry Reedy <tjreedy@udel.edu> - 2014-03-05 18:00 -0500
                Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-06 03:01 +0000
                Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 22:03 -0800
                Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-05 17:26 +1100
                Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 17:32 +1100
                Re: Reference Tim Chase <python.list@tim.thechases.com> - 2014-03-05 08:24 -0600
                Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-05 18:29 +0000
                Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 22:34 +0200
                Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 08:01 +1100
                Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 23:14 +0200
                Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-06 08:26 +1100
                Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 23:50 +0200
                Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-06 00:35 +0000
                Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-06 11:50 +1100
                Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-06 17:46 +0000
                Re: Reference Tim Chase <python.list@tim.thechases.com> - 2014-03-05 15:33 -0600
                Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 08:37 +1100
                Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-06 02:52 +0200
                Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-06 12:05 +1100
                Re: Reference alex23 <wuwei23@gmail.com> - 2014-03-06 12:12 +1000
                Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-05 21:46 +0000
                Re: Reference Marko Rauhamaa <marko@pacujo.net> - 2014-03-05 08:23 +0200
                Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 22:33 -0800
                Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-05 17:40 +1100
                Re: Reference Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-03-05 12:35 +0000
                Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 23:45 +1100
          Re: Reference Jerry Hill <malaclypse2@gmail.com> - 2014-03-04 10:19 -0500
            Re: Reference Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-03-04 15:42 +0000
              Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 03:02 +1100
                Re: Reference Roy Smith <roy@panix.com> - 2014-03-04 11:14 -0500
              Re: Reference MRAB <python@mrabarnett.plus.com> - 2014-03-04 17:12 +0000
            Re: Reference Rustom Mody <rustompmody@gmail.com> - 2014-03-04 08:24 -0800
          Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 02:25 +1100
          Re: Reference Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2014-03-05 14:37 +0100
      Re: Reference Steven D'Aprano <steve@pearwood.info> - 2014-03-04 03:59 +0000
    Re: Reference Ben Finney <ben+python@benfinney.id.au> - 2014-03-04 09:17 +1100
      Re: Reference Roy Smith <roy@panix.com> - 2014-03-03 18:02 -0500
        Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-04 10:09 +1100
        Re: Reference Steven D'Aprano <steve@pearwood.info> - 2014-03-04 04:38 +0000
  Re: Reference Terry Reedy <tjreedy@udel.edu> - 2014-03-03 13:48 -0500
    Re: Reference Steven D'Aprano <steve@pearwood.info> - 2014-03-04 03:45 +0000
    Re: Reference Alexander Blinne <news@blinne.net> - 2014-03-04 13:55 +0100
      Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 01:06 +1100
        Re: Reference Alexander Blinne <news@blinne.net> - 2014-03-04 22:53 +0100
          Re: Reference Chris Angelico <rosuav@gmail.com> - 2014-03-05 09:01 +1100

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