Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!bcyclone04.am1.xlned.com!bcyclone04.am1.xlned.com!newsfeed.xs4all.nl!newsfeed1a.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
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 0.003
X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'argument': 0.05; '[0]': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; '"x"': 0.16; 'argument.': 0.16; 'declared': 0.16; 'message-id:@4ax.com': 0.16; 'mutable': 0.16; 'no...': 0.16; 'overloaded': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'wed,': 0.18; 'passing': 0.19; 'url:home': 0.24; 'header:X -Complaints-To:1': 0.27; 'function': 0.29; 'code': 0.31; '+0100,': 0.31; '>>>>': 0.31; 'implemented': 0.33; 'something': 0.35; 'curious': 0.36; 'charset:us-ascii': 0.36; 'implement': 0.38; 'nov': 0.38; 'to:addr:python-list': 0.38; 'previous': 0.38; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'forum': 0.61; 'default': 0.69; 'saw': 0.77; 'received:108': 0.93
X-Injected-Via-Gmane: http://gmane.org/
To: python-list@python.org
From: Dennis Lee Bieber <wlfraed@ix.netcom.com>
Subject: Re: Curious function argument
Date: Wed, 12 Nov 2014 09:18:30 -0500
Organization: IISS Elusive Unicorn
References: <54635bce$0$2384$426a74cc@news.free.fr>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Gmane-NNTP-Posting-Host: adsl-108-79-223-190.dsl.klmzmi.sbcglobal.net
X-Newsreader: Forte Agent 6.00/32.1186
X-No-Archive: YES
X-BeenThere: python-list@python.org
X-Mailman-Version: 2.1.15
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>
Newsgroups: comp.lang.python
Message-ID: <mailman.15721.1415801914.18130.python-list@python.org>
Lines: 39
NNTP-Posting-Host: 2001:888:2000:d::a6
X-Trace: 1415801914 news.xs4all.nl 2855 [2001:888:2000:d::a6]:38526
X-Complaints-To: abuse@xs4all.nl
X-Received-Bytes: 3359
X-Received-Body-CRC: 3862729768
Xref: csiph.com comp.lang.python:80605

On Wed, 12 Nov 2014 14:07:14 +0100, "ast" <nomail@invalid.com> declaimed
the following:

>Hello
>
>I saw in a code from a previous message in this forum
>a curious function argument.
>
>def test(x=[0]):
>   print(x[0])   ## Poor man's object
>   x[0] += 1
>
>>>> test()
>0
>>>> test()
>1
>>>> test()
>2
>>>> 
>
>I understand that the author wants to implement a global
>variable x . It would be better to write 'global x' inside the
>function.
>
	No... The author implemented a mutable DEFAULT argument.

	The argument can still be overloaded by passing something else into the
function.

y = [0]
z = 234
test(y)
test(z)

	This would not work if one instead declared a global "x"
-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
    wlfraed@ix.netcom.com    HTTP://wlfraed.home.netcom.com/