Path: csiph.com!usenet.pasdenom.info!aioe.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed4.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail
Return-Path: <andrea.crotti.0@gmail.com>
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; '(1,': 0.09; '3),': 0.09; '5),': 0.09; 'behave': 0.09; 'res': 0.09; 'to:name:python-list': 0.15; '(2,': 0.16; '2),': 0.16; '3)]': 0.16; 'after,': 0.16; 'iterating': 0.16; 'possible?': 0.16; 'res:': 0.16; 'result:': 0.16; 'trying': 0.21; '(which': 0.26; 'message- id:@mail.gmail.com': 0.27; 'received:209.85.212': 0.28; 'noticed': 0.28; 'print': 0.32; 'to:addr:python-list': 0.33; 'received:google.com': 0.34; 'list': 0.35; 'received:209.85': 0.35; 'but': 0.36; 'should': 0.36; 'received:209': 0.37; 'to:addr:python.org': 0.39; 'first': 0.61; 'strange': 0.62
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:x-received:date:message-id:subject:from:to :content-type; bh=Kjyj3oOeer9rvvh0SCmcC2d9CrxOyHLt9BsMmqTFLaE=; b=u+Ae0GKTBqmK66TXcG9rMuDHQqp29hrskREuQdB/v8zPY3WUCroUuQGoqJeV4KsJp/ vj5QEPCMrLQsgZ527YBkXd2pUYojSh/KAkyUqRRJ8KoRsvCTbA/wigSC41Ll1TuhmGCt EJN+Iu86d6KyP1V+fUUBcRZnNuh4xOk05BBZzHxld8feWIoOwlk1UPIzxUkp2w9VyfyH oKSbgQhU1FfegUI05mIbiz65t+QtDDDKtqRmlonGF33UiinqYfi5tLj16Euxg2bkDRfR xJI/0ux5KXKY58KRUBjZrPNYv3dqCXsCvnXd7II3BMC58KAhPIVY2QFNSuqH/5beZH8c fuaA==
MIME-Version: 1.0
X-Received: by 10.180.108.229 with SMTP id hn5mr20629947wib.28.1361896072859; Tue, 26 Feb 2013 08:27:52 -0800 (PST)
Date: Tue, 26 Feb 2013 16:27:43 +0000
Subject: groupby behaviour
From: andrea crotti <andrea.crotti.0@gmail.com>
To: python-list <python-list@python.org>
Content-Type: text/plain; charset=ISO-8859-1
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>
Newsgroups: comp.lang.python
Message-ID: <mailman.2550.1361896083.2939.python-list@python.org>
Lines: 32
NNTP-Posting-Host: 2001:888:2000:d::a6
X-Trace: 1361896083 news.xs4all.nl 6872 [2001:888:2000:d::a6]:50189
X-Complaints-To: abuse@xs4all.nl
Xref: csiph.com comp.lang.python:39966

So I was trying to use groupby (which I used in the past), but I
noticed a very strange thing if using list on
the result:

In [109]: s = sorted(s, key=keyfunc)

In [110]: s
Out[110]: [(1, 2), (1, 3), (1, 5), (2, 3)]


In [117]: m2 = list(groupby(s, keyfunc))

In [118]: for name, res in m2:
   .....:     for r in res:
   .....:         print name, r
   .....:
2 (2, 3)

In [119]: m2 = groupby(s, keyfunc)

In [120]: for name, res in m2:
    for r in res:
        print name, r
   .....:
1 (1, 2)
1 (1, 3)
1 (1, 5)
2 (2, 3)

How is that possible?
Generating the list first should be the same as iterating after, how
can it behave differently?