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To: python-list@python.org
From: Ben Finney <ben+python@benfinney.id.au>
Subject: Re: Reference
Date: Thu, 06 Mar 2014 08:37:19 +1100
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Xref: csiph.com comp.lang.python:67885

Marko Rauhamaa <marko@pacujo.net> writes:

> Ben Finney <ben+python@benfinney.id.au>:
>
> > A reference-compliant implementation can contradict your inference (by
> > returning an object identity that is *not* the object's memory
> > address). Any code you've written based on that false inference will
> > break.
> >
> > The fault will be yours, for inferring an assertion that isn't implied
> > by the definition.
>
> Show me a few lines of Python that demonstrate the error of the false
> inference, please.

It need not be Python; it could be an extension library to which you
pass the ‘id(foo)’ result, on the false assumption that it must be a
memory location.

Besides which, it is *you* that declares this abstraction to be leaky.
If you're unable to show how that's the case, I rest on the null
hypothesis: your assertion is untrue.

> When I talk about an object's memory address, I'm not referring to
> what might be revealed by gdb, for example. That is, I'm not talking
> about the process's virtual address space, nor am I talking about the
> physical address on the address bus. I can simply define that the
> object's memory address is whatever id() returns.

Then this does not count as a leaky abstraction. All you're saying is
that the ‘id(foo)’ result is a representation of the object identity,
which is entirely at the level of the abstraction. Nothing is leaked.

-- 
 \      “God forbid that any book should be banned. The practice is as |
  `\                  indefensible as infanticide.” —Dame Rebecca West |
_o__)                                                                  |
Ben Finney