Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder1.news.weretis.net!feeder.erje.net!eu.feeder.erje.net!newsfeed.freenet.ag!news2.euro.net!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
To: python-list@python.org
From: John Reid <j.reid@mail.cryst.bbk.ac.uk>
Subject: Re: Differences creating tuples and collections.namedtuples
Date: Mon, 18 Feb 2013 14:23:02 +0000
References: <7a40a426-baa9-46f8-8f9d-59ba32b044f3@googlegroups.com> <51221A6C.3030804@davea.name> <5122360C.20603@mail.cryst.bbk.ac.uk> <CAHVvXxQJZmvKuhOG_Nfytv+zyg96n7HtX6G=SNwWkZUZW8ZOng@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1
Content-Transfer-Encoding: 7bit
Cc: Python List <python-list@python.org>
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130106 Thunderbird/17.0.2
In-Reply-To: <CAHVvXxQJZmvKuhOG_Nfytv+zyg96n7HtX6G=SNwWkZUZW8ZOng@mail.gmail.com>
Precedence: list
Newsgroups: comp.lang.python
Message-ID: <mailman.1946.1361197396.2939.python-list@python.org>
Lines: 41
NNTP-Posting-Host: 2001:888:2000:d::a6
Xref: csiph.com comp.lang.python:39096



On 18/02/13 14:15, Oscar Benjamin wrote:
> On 18 February 2013 14:09, John Reid <j.reid@mail.cryst.bbk.ac.uk> wrote:
>> On 18/02/13 12:11, Dave Angel wrote:
>>> On 02/18/2013 06:47 AM, John Reid wrote:
>>>> Hi,
>>>>
>>>> I was hoping namedtuples could be used as replacements for tuples in
>>>> all instances. There seem to be some differences between how tuples
>>>> and namedtuples are created. For example with a tuple I can do:
>>>>
>>>> a=tuple([1,2,3])
>>>>
>>>> with namedtuples I get a TypeError:
>>>>
>>>> from collections import namedtuple
>>>> B=namedtuple('B', 'x y z')
>>>> b=B([1,2,3])
>>>
>>> You are passing a single list to the constructor, but you specified that
>>> the namedtuple was to have 3 items.  So you need two more.
>>
>> I'm aware how to construct the namedtuple and the tuple. My point was
>> that they use different syntaxes for the same operation and this seems
>> to break ipython. I was wondering if this is a necessary design feature
>> or perhaps just an oversight on the part of the namedtuple author or
>> ipython developers.
> 
> I would say that depending on isinstance(obj, tuple) was the error. I
> can't offer a suggestion as you haven't clarified what the purpose of
> this code in canSequence() is or what constraints it is expected to
> satisfy.
> 

Like I said it is not my code. I'm hoping the IPython developers can
help me out here. That said it would be nice to know the rationale for
namedtuple.__new__ to have a different signature to tuple.__new__. I'm
guessing namedtuple._make has a similar interface to tuple.__new__. Does
anyone know what the rationale was for this design?