Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!1.eu.feeder.erje.net!eternal-september.org!feeder.eternal-september.org!mx02.eternal-september.org!.POSTED!not-for-mail
From: Nobody <nobody@nowhere.invalid>
Newsgroups: comp.lang.python
Subject: Re: So what's happening here?
Date: Fri, 05 Jun 2015 15:13:56 +0100
Organization: A noiseless patient Spider
Lines: 31
Message-ID: <pan.2015.06.05.14.16.06.63000@nowhere.invalid>
References: <pan.2015.06.05.12.46.21@nowhere.invalid> <mailman.196.1433508938.13271.python-list@python.org> <pan.2015.06.05.13.11.13@nowhere.invalid>
Mime-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
Injection-Info: mx02.eternal-september.org; posting-host="152d4dee6f95183c956ee6fa63d7e69f"; logging-data="11320"; mail-complaints-to="abuse@eternal-september.org";	posting-account="U2FsdGVkX1+FKOVZPwyHoTFYaW1TLRoJ"
User-Agent: Pan/0.14.2 (This is not a psychotic episode. It's a cleansing moment of clarity.)
Cancel-Lock: sha1:6zHngrZyZ5ezU6mqtdiOma5pDNs=
Xref: csiph.com comp.lang.python:92153

On Fri, 05 Jun 2015 13:11:13 +0000, Paul Appleby wrote:

> (I'd have thought that id(a[1]) and id(b[1]) would be the same if they
> were the same element via different "views", but the id's seem to change
> according to rules that I can't fathom.)

First, a[1] and b[1] aren't views, they're scalars.

Second, different views on the same data are different objects, they just
share the same underlying data. Consider the case where the slice doesn't
cover the entire range:

> a = np.array([1,2,3])
> b = a[:2]
> a
array([1, 2, 3])
> b
array([1, 2])
> id(a)
139682716078288
> id(b)
139682716078368
> b[0] = 99
> a
array([99,  2,  3])
> b
array([99,  2])

The case where a slice *does* cover the entire range isn't special; the
resulting view is still a different object.