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Date: Sat, 15 Feb 2014 17:07:17 +1100
Subject: Re: Explanation of list reference
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
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On Sat, Feb 15, 2014 at 4:36 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> References can be names like `mystring`, or list items `mylist[0]`, or
> items in mappings `mydict["key"]`, or attributes `myobject.attr`, or even
> expressions `x+y*(1-z)`.

I agree with most of what you've said, but I'm not sure I like that
last bit. The expression evaluates to an object, yes, but it's not
itself a reference... is it? It has references to x, y, 1, and z, but
it's not itself a reference to anything. If you take a reference and
assign it to a name, and take that same reference and assign it to
another name, I would expect those two names to now refer to the same
object:

>>> lst = [1000, 2000, 3000]
>>> x = lst[1]
>>> y = lst[1]
>>> x is y
True

But with expressions, it's not so, and new objects may be created. The
expression isn't a reference to its result, but it can yield an
object, which it (naturally) does by reference.

ChrisA