Path: csiph.com!usenet.pasdenom.info!news.albasani.net!newsfeed.freenet.ag!news2.euro.net!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path: <joan4eric@gmail.com>
X-Original-To: python-list@python.org
Delivered-To: python-list@mail.python.org
X-Spam-Status: OK 0.115
X-Spam-Level: *
X-Spam-Evidence: '*H*': 0.77; '*S*': 0.00; 'calculating': 0.09; 'explanation': 0.09; 'friday,': 0.09; 'to:addr:comp.lang.python': 0.09; 'cc:addr:python-list': 0.11; 'python': 0.11; 'def': 0.12; 'bug': 0.12; 'helps!': 0.16; 'terminate.': 0.16; 'wrote:': 0.18; 'code.': 0.18; '>>>': 0.22; 'example': 0.22; 'otherwise,': 0.22; 'cc:addr:python.org': 0.22; 'header:User-Agent:1': 0.23; 'cc:2**0': 0.24; 'cc:no real name:2**0': 0.24; 'header:In-Reply- To:1': 0.27; 'function': 0.29; 'rest': 0.29; 'chris': 0.29; 'am,': 0.29; '(like': 0.30; 'closer': 0.31; 'comparison': 0.31; 'depth': 0.31; 'douglas': 0.31; 'critical': 0.32; 'quite': 0.32; 'running': 0.33; 'fri,': 0.33; 'case,': 0.35; 'no,': 0.35; 'but': 0.35; 'received:google.com': 0.35; 'explains': 0.36; 'found.': 0.36; 'list': 0.37; 'list.': 0.37; 'sometimes': 0.38; 'thank': 0.38; 'rather': 0.38; 'itself': 0.39; 'how': 0.40; 'eventually': 0.60; 'is.': 0.60; 'simple,': 0.60; 'hope': 0.61; 'march': 0.61; 'numbers': 0.61; 'further': 0.61; 'first': 0.61; 'maximum': 0.63; 'sum': 0.64; 'mar': 0.68; 'answer.': 0.68; 'results': 0.69; 'receive': 0.70; 'anyone.': 0.74; 'obvious': 0.74; 'condition.': 0.84; 'obvious.': 0.84; 'standing': 0.84; 'exceeded': 0.97; '2013': 0.98
X-Received: by 10.50.186.202 with SMTP id fm10mr45529igc.10.1364593651661; Fri, 29 Mar 2013 14:47:31 -0700 (PDT)
Newsgroups: comp.lang.python
Date: Fri, 29 Mar 2013 14:47:31 -0700 (PDT)
In-Reply-To: <mailman.3946.1364556269.2939.python-list@python.org>
Complaints-To: groups-abuse@google.com
Injection-Info: glegroupsg2000goo.googlegroups.com; posting-host=122.151.66.173; posting-account=JzVE4wkAAADCSo8EXJLK0dGqAu47aMvq
References: <e45b8b75-ff89-4ee1-9ada-bfda3d06d05d@googlegroups.com> <9dla2a-kql.ln1@satorlaser.homedns.org> <5ce10a13-be58-4548-85df-e1d865d3304e@googlegroups.com> <mailman.3857.1364445382.2939.python-list@python.org> <f160e316-e2f6-4314-827e-9d48007f7f70@googlegroups.com> <mailman.3946.1364556269.2939.python-list@python.org>
User-Agent: G2/1.0
X-Google-Web-Client: true
X-Google-IP: 122.151.66.173
MIME-Version: 1.0
Subject: Re: Sudoku
From: Eric Parry <joan4eric@gmail.com>
To: comp.lang.python@googlegroups.com
Content-Type: text/plain; charset=ISO-8859-1
Cc: python-list@python.org
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: <http://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: <http://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Message-ID: <mailman.3968.1364594426.2939.python-list@python.org>
Lines: 72
NNTP-Posting-Host: 2001:888:2000:d::a6
X-Trace: 1364594426 news.xs4all.nl 6963 [2001:888:2000:d::a6]:47925
X-Complaints-To: abuse@xs4all.nl
Xref: csiph.com comp.lang.python:42284

On Friday, March 29, 2013 9:15:36 AM UTC+10:30, Chris Angelico wrote:
> On Fri, Mar 29, 2013 at 9:11 AM, Eric Parry <joan4eric@gmail.com> wrote:
> 
> > Thank you for that explanation.
> 
> > No, I do not understand recursion. It is missing from my Python manual. I would be pleased to receive further explanation from anyone.
> 
> 
> 
> If you already know what recursion is, just remember the answer.
> 
> Otherwise, find someone who is standing closer to Douglas Hofstadter
> 
> than you are; then ask him or her what recursion is.
> 
> 
> 
> :)
> 
> 
> 
> Recursion is a form of self-referential code. Take this simple, and
> 
> rather silly, means of calculating the sum of numbers in a list (like
> 
> the sum() function):
> 
> 
> 
> # The sum of numbers in an empty list is 0.
> 
> # Otherwise it is the first number plus the sum of the rest of the list.
> 
> def list_sum(lst):
> 
>     if not lst: return 0
> 
>     return lst[0] + list_sum(lst[1:])
> 
> 
> 
> >>> list_sum([1,2,3,4,5,6])
> 
> 21
> 
> 
> 
> Note how the function calls itself - but not always. That's critical
> 
> to recursion - a termination condition. In this case, it's quite
> 
> obvious that the list will eventually have nothing left in it, so the
> 
> function will terminate. Sometimes it's less obvious. Sometimes a bug
> 
> results in infinite recursion... and:
> 
> 
> 
> RuntimeError: maximum recursion depth exceeded in comparison
> 
> 
> 
> Hope that helps!
> 
> 
> 
> ChrisA

Thank you for that example Chris.
That explains why the program keeps running after a solution is found.
Eric