Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder1.news.weretis.net!feeder.erje.net!eu.feeder.erje.net!newsfeed.xs4all.nl!newsfeed3.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
To: python-list@python.org
From: Ben Finney <ben+python@benfinney.id.au>
Subject: Re: list storing variables
Date: Tue, 24 Feb 2015 09:03:18 +1100
References: <54eb2357$0$3011$426a74cc@news.free.fr>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.4 (gnu/linux)
Cancel-Lock: sha1:SoVKGtFBPQS7pT7l5BIL65Zd84Q=
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.19104.1424728988.18130.python-list@python.org>
Lines: 42
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:86271

"ast" <nomail@invalid.com> writes:

> Ok, a change in a or b doesn't impact Li. This works as expected

Because a container stores references to objects. The other references
(such as names) that object might have are not stored.

> Is there a way to define a container object able to store some
> variables so that a change of a variable make a change in this object
> content ?

As has been pointed out, Python does not have “variables” in the sense
of a named box containing a value.

What Python does have is a mapping type. You can store a key → value
mapping for each value you want to reference later.

    >>> a = 2; b = 5
    >>> foo = {'a': a, 'b': b}
    >>> foo
    {'b': 5, 'a': 2}
    >>> foo['a'] = 3
    >>> foo
    {'b': 5, 'a': 3}

You appear, though, to want this to somehow automatically track the
changes in name bindings. No, there's no way to do that except
explicitly coding it yourself.

> In C language, there is &A for address of A

There is no “address of a value” concept in Python. You access a value
by some reference, either a name or an item in a collection. When a
reference changes to reference some different value, other references
are not affected.

-- 
 \        “All opinions are not equal. Some are a very great deal more |
  `\   robust, sophisticated, and well supported in logic and argument |
_o__)                                     than others.” —Douglas Adams |
Ben Finney