Path: csiph.com!feeder.erje.net!2.eu.feeder.erje.net!newsfeed.kamp.net!newsfeed.kamp.net!fu-berlin.de!uni-berlin.de!not-for-mail
From: Terry Reedy <tjreedy@udel.edu>
Newsgroups: comp.lang.python
Subject: Re: subscripting Python 3 dicts/getting the only value in a Python 3 dict
Date: Tue, 12 Jan 2016 12:12:43 -0500
Lines: 52
Message-ID: <mailman.73.1452618784.13488.python-list@python.org>
References: <f2711b57-7b11-4fd5-8bab-a3e8581177b5@googlegroups.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
X-Trace: news.uni-berlin.de 59TnBoxYKjJycMKzzcIxtQSnl8ywllqweVAMiKMS0STg==
Return-Path: <python-python-list@m.gmane.org>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
X-Spam-Status: OK 0.000
X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'subject:Python': 0.05; 'preferably': 0.05; 'indexing': 0.07; 'subject:getting': 0.07; 'dict': 0.09; 'item,': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'typeerror:': 0.09; 'python': 0.10; 'jan': 0.11; 'subject: \n ': 0.15; 'iterated': 0.16; 'nick': 0.16; 'received:80.91.229.3': 0.16; 'received:io': 0.16; 'received:plane.gmane.org': 0.16; 'received:psf.io': 0.16; 'reedy': 0.16; 'wrote:': 0.16; '>>>': 0.20; 'all,': 0.20; '"",': 0.22; 'problem:': 0.22; 'am,': 0.23; '(most': 0.24; 'header:In- Reply-To:1': 0.24; 'header:User-Agent:1': 0.26; 'header:X -Complaints-To:1': 0.26; 'respective': 0.27; 'data,': 0.27; 'yield': 0.27; "skip:' 10": 0.28; 'values': 0.28; 'dictionary': 0.29; 'seemingly': 0.29; 'subject:/': 0.30; 'code': 0.30; "i'd": 0.31; 'traceback': 0.33; 'file': 0.34; 'membership': 0.34; 'item': 0.35; 'there': 0.36; 'received:71': 0.36; 'to:addr:python-list': 0.36; 'subject:: ': 0.37; 'received:org': 0.37; 'one,': 0.37; 'end': 0.39; 'whatever': 0.39; 'does': 0.39; 'subject:the': 0.39; 'to:addr:python.org': 0.40; 'where': 0.40; 'skip:n 10': 0.62; 'is.': 0.63; 'obvious': 0.76; 'it"': 0.84; 'subject:value': 0.84; 'received:fios.verizon.net': 0.91; 'write:': 0.91
X-Injected-Via-Gmane: http://gmane.org/
X-Gmane-NNTP-Posting-Host: pool-71-185-227-36.phlapa.fios.verizon.net
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:38.0) Gecko/20100101 Thunderbird/38.5.1
In-Reply-To: <f2711b57-7b11-4fd5-8bab-a3e8581177b5@googlegroups.com>
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.20+
Precedence: list
List-Id: General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe: <https://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive: <http://mail.python.org/pipermail/python-list/>
List-Post: <mailto:python-list@python.org>
List-Help: <mailto:python-list-request@python.org?subject=help>
List-Subscribe: <https://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Xref: csiph.com comp.lang.python:101556

On 1/12/2016 11:50 AM, Nick Mellor wrote:
> Hi all,
>
> Seemingly simple problem:
>
> There is a case in my code where I know a dictionary has only one item in it. I want to get the value of that item, whatever the key is.
>
> In Python2 I'd write:
>
>>>> d = {"Wilf's Cafe": 1}
>>>> d.values()[0]
> 1
>
> and that'd be an end to it.
>
> In Python 3:
>
>>>> d = {"Wilf's Cafe": 1}
>>>> d.values()[0]
> Traceback (most recent call last):
>    File "<input>", line 1, in <module>
> TypeError: 'dict_values' object does not support indexing

The intended use of dict views: "Dictionary views can be iterated over 
to yield their respective data, and support membership tests:"

> "Wilf's Cafe"
>>>> d[list(d)[0]]
> 1
>
>>>> for k in d:
> ...     value = d[k]
> ...     break
> ...
>>>> value
> 1
>
>>>> list(d.values())[0]
> 1
>
> None of this feels like the "one, and preferably only one,
 > obvious way to do it" we all strive for. Any other ideas?

Using the values views at intended (as an iterable):

 >>> dv = d.values()
 >>> next(iter(dv))
1

-- 
Terry Jan Reedy