Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!aioe.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed5.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 0.003 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'socket': 0.04; 'francis': 0.07; 'subject:while': 0.07; 'python': 0.08; 'difference,': 0.09; 'erik': 0.09; 'iterate': 0.09; 'loop.': 0.09; 'received:209.85.210.174': 0.13; 'received:mail- iy0-f174.google.com': 0.13; 'cc:addr:python-list': 0.15; 'this:': 0.15; '"while': 0.16; 'latter,': 0.16; 'obviously,': 0.16; 'socket.': 0.16; 'worried': 0.16; 'wrote:': 0.16; '>>>': 0.18; 'example.': 0.18; 'level,': 0.18; '\xa0so': 0.18; 'cc:no real name:2**0': 0.21; 'header:In-Reply-To:1': 0.22; 'obviously': 0.23; '\xa0if': 0.23; 'cc:2**0': 0.25; 'right.': 0.25; 'url:mailman': 0.26; 'url:code': 0.28; 'message-id:@mail.gmail.com': 0.28; 'example': 0.28; 'explicitly': 0.28; 'cc:addr:python.org': 0.29; 'times.': 0.30; 'cases.': 0.30; 'url:listinfo': 0.30; '---': 0.31; 'actually': 0.32; "can't": 0.32; "isn't": 0.32; "won't": 0.33; 'instead': 0.33; 'loop': 0.34; 'majority': 0.34; 'too': 0.34; 'rather': 0.34; 'certain': 0.34; 'ca,': 0.34; 'changing': 0.34; 'from:charset:iso-8859-1': 0.34; '...': 0.35; 'something': 0.35; 'file': 0.35; 'url:python': 0.36; 'executing': 0.36; 'minimal': 0.36; 'things,': 0.36; 'but': 0.37; "there's": 0.37; 'received:google.com': 0.37; 'using': 0.37; 'some': 0.38; 'received:209.85': 0.38; 'think': 0.38; 'speak': 0.38; 'skip:\xa0 10': 0.38; 'url:org': 0.39; 'point': 0.39; 'either': 0.39; 'being': 0.39; 'received:209': 0.39; 'subject:: ': 0.39; 'difference': 0.40; 'most': 0.60; 'chance': 0.62; 'url:p': 0.62; 'skip:1 10': 0.63; 'overall': 0.66; 'usa': 0.66; 'friend': 0.69; 'with,': 0.73; 'defensive': 0.84; 'imagine,': 0.84 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=BMc9Knb8HmI/eyZNv8/u7Fletmkw0pT5TyEYfvLAI1k=; b=qvUJ3nhnMThcHRP+/Qttdep3HAaL3CqaitXjjGroffHOOwqisM8p0wc0y59K1XSFT6 zx2fPgEA88C8o72wxebRKBEMWcqXDTnImM/Xkk3W7lZFwilh7OO9K2m3CGLhTOeK6L1F loEZ4tM99AaSeqFl4ipy1f9RPBNCnvH0MQ9SM= MIME-Version: 1.0 In-Reply-To: <4v6dnYAfTu69LIDSnZ2dnUVZ5r6dnZ2d@giganews.com> References: <4F1AC1D4.2080402@gmail.com> <4v6dnYAfTu69LIDSnZ2dnUVZ5r6dnZ2d@giganews.com> Date: Mon, 23 Jan 2012 21:20:23 +0100 Subject: Re: while True or while 1 From: =?ISO-8859-1?Q?Giampaolo_Rodol=E0?= To: Erik Max Francis Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: python-list@python.org 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: 72 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1327350029 news.xs4all.nl 6928 [2001:888:2000:d::a6]:50162 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:19282 Il 23 gennaio 2012 20:12, Erik Max Francis ha scritto: > Giampaolo Rodol=E0 wrote: >> >> Il 21 gennaio 2012 22:13, Erik Max Francis ha scritto: >>> >>> The real reason people still use the `while 1` construct, I would >>> imagine, >>> >>> is just inertia or habit, rather than a conscious, defensive decision. >>> =A0If >>> it's the latter, it's a case of being _way_ too defensive. >> >> >> It's also because while 1 is faster: > > =A0 =A0 =A0 =A0... >> >> while True: 1.41121292114 >> while 1: =A0 =A0 =A01.07101011276 >> >> Most of the times tha't won't make any noticeable difference, but it's >> also true that certain while loops are going to iterate milions of >> times. >> Think about receiving a 10 GB file by using a socket. You'd tipically >> have something like this: >> >> while 1: >> =A0 =A0chunk =3D sock.recv(1024): >> =A0 =A0if not chunk: >> =A0 =A0 =A0 =A0 =A0break >> =A0 =A0 ... >> >> Now, that's a case where I (personally) want to explicitly use "while >> >> 1" instead of "while True". > > > Such a loop would obviously be I/O-bound, not CPU-bound. =A0So changing t= he > form of the while loop would make minimal difference to its overall > performance. =A0It'd be spending the vast majority of its time blocked at= the > OS socket level, not executing the condition of the while loop. > > As with most of these things, if one is this worried about performance, t= hen > either Python was the wrong choice to begin with, or there's a good chanc= e > that you're worried about something that isn't actually where the bottlen= eck > is in the first place. > > > -- > Erik Max Francis && max@alcyone.com && http://www.alcyone.com/max/ > =A0San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Jabber erikmaxfrancis > =A0Think twice before you speak to a friend in need. > =A0 -- Ambrose Bierce > -- > http://mail.python.org/mailman/listinfo/python-list Obviously, you're right. I picked up the wrong example. My point is 1.41121292114 vs 1.07101011276 *might* make some difference in certain cases. I just can't come up with a good example where that would be justified. =3D= ) --- Giampaolo http://code.google.com/p/pyftpdlib/ http://code.google.com/p/psutil/ http://code.google.com/p/pysendfile/