Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!feeder.news-service.com!newsfeed.xs4all.nl!newsfeed6.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.001 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'else:': 0.03; 'instance,': 0.05; 'empty,': 0.09; 'iterate': 0.09; 'to:name:python list': 0.09; 'tuple': 0.09; 'pm,': 0.11; 'output': 0.12; 'slightly': 0.12; 'def': 0.13; 'am,': 0.14; 'wrote:': 0.14; 'bye': 0.16; 'definition,': 0.16; 'empty"': 0.16; 'numpy': 0.16; 'pythonic': 0.16; 'received:mindspring.com': 0.16; 'set,': 0.16; 'thanks,': 0.17; 'subject:list': 0.22; 'header:In-Reply-To:1': 0.22; 'way?': 0.23; 'function': 0.27; '"the': 0.28; 'definition': 0.29; 'problem': 0.29; 'hi,': 0.29; 'list': 0.30; 'to:addr:python-list': 0.32; '...': 0.32; 'there': 0.35; 'print': 0.35; 'list,': 0.36; 'charset:us-ascii': 0.36; 'but': 0.38; 'to:addr:python.org': 0.39; 'header:Mime-Version:1': 0.39; 'received:24': 0.39; "it's": 0.40; 'philip': 0.60; 'header:Message-Id:1': 0.62; '(3)': 0.64; 'care': 0.67; 'received:69.73': 0.84 Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 (Apple Message framework v1084) Subject: Re: checking if a list is empty From: Philip Semanchuk In-Reply-To: <200e93c2-6b87-4113-9c6f-85815e51ea77@28g2000yqu.googlegroups.com> Date: Fri, 6 May 2011 18:21:09 -0400 Content-Transfer-Encoding: quoted-printable References: <200e93c2-6b87-4113-9c6f-85815e51ea77@28g2000yqu.googlegroups.com> To: Python list X-Mailer: Apple Mail (2.1084) X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - deimos.nocdirect.com X-AntiAbuse: Original Domain - python.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - semanchuk.com X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 65 NNTP-Posting-Host: 82.94.164.166 X-Trace: 1304723070 news.xs4all.nl 41113 [::ffff:82.94.164.166]:33224 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:4873 On May 6, 2011, at 5:57 PM, scattered wrote: > On May 6, 2:36 am, Jabba Laci wrote: >> Hi, >>=20 >> If I want to check if a list is empty, which is the more pythonic = way? >>=20 >> li =3D [] >>=20 >> (1) if len(li) =3D=3D 0: >> ... >> or >> (2) if not li: >> ... >>=20 >> Thanks, >>=20 >> Laszlo >=20 > is there any problem with >=20 > (3) if li =3D=3D []: >=20 > ? What if it's not a list but a tuple or a numpy array? Often I just want = to iterate through an element's items and I don't care if it's a list, = set, etc. For instance, given this function definition -- def print_items(an_iterable): if not an_iterable: print "The iterable is empty" else: for item in an_iterable: print item I get the output I want with all of these calls: print_items( list() ) print_items( tuple() ) print_items( set() ) print_items( numpy.array([]) ) Given this slightly different definition, only the first call gives me = the output I expect:=20 def print_items(an_iterable): if an_iterable =3D=3D []: print "The iterable is empty" else: for item in an_iterable: print item I find I use the the former style ("if not an_iterable") almost = exclusively. bye Philip