Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!weretis.net!feeder1.news.weretis.net!feeder.erje.net!newsfeed.xs4all.nl!newsfeed6.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!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 0.028 X-Spam-Evidence: '*H*': 0.94; '*S*': 0.00; 'interpreter': 0.05; 'subject:while': 0.07; 'def': 0.13; 'cc:addr:python-list': 0.15; '"while': 0.16; 'boolean': 0.16; 'invalidate': 0.16; 'matteo': 0.16; 'wrote:': 0.16; 'cc:no real name:2**0': 0.21; 'maybe': 0.21; "doesn't": 0.22; 'header:In-Reply-To:1': 0.22; 'wrong?': 0.23; 'cc:2**0': 0.25; 'sender:addr:gmail.com': 0.25; 'code': 0.25; 'url:mailman': 0.26; 'tried': 0.27; 'fact': 0.27; 'looks': 0.27; 'pass': 0.28; 'true,': 0.28; 'cc:addr:python.org': 0.29; 'logic': 0.30; 'url:listinfo': 0.30; 'anyone': 0.31; 'that,': 0.32; 'header :User-Agent:1': 0.33; 'instead': 0.33; 'there': 0.33; 'loop': 0.34; 'probably': 0.35; '...': 0.35; 'url:python': 0.36; 'equal': 0.36; '(to': 0.36; 'charset:us-ascii': 0.36; 'but': 0.37; 'received:google.com': 0.37; 'using': 0.37; 'received:209.85': 0.38; 'think': 0.38; 'sometimes': 0.38; 'url:org': 0.39; 'why': 0.39; 'received:209': 0.39; 'received:78': 0.39; 'subject:: ': 0.39; 'difference': 0.40; 'url:net': 0.61; 'more': 0.61; 'presented': 0.62; 'below:': 0.80; 'andrea': 0.84; '13)': 0.93 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=sender:date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=8tOc2l4fXb3kg8ZJADDKQciTHB/+lP1wfQhhJc0ytm0=; b=kxNOIAklEFHZNAirWjsxit2ibxOr/lDaC7azbVa312xAd0nAH3KaG+OBHw90ViW5mx iLoHau4jVSe/nc0WAi7DmaLOiJeUt/i7pdsv1x7j+cL/yYPRyTiy6pE9fULa+/v29ryD dDGSuZJDiBHw0D9kXmvvs9K6jyejApnq3R+oM= Sender: Matteo Landi Date: Sat, 21 Jan 2012 16:24:09 +0100 From: Matteo Landi To: Andrea Crotti Subject: Re: while True or while 1 References: <4F1AC1D4.2080402@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4F1AC1D4.2080402@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) 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: 57 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1327159453 news.xs4all.nl 6940 [2001:888:2000:d::a6]:41926 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:19192 Probably because of the fact it is possible to set True equal to False and consequently then invalidate loop logic as presented below: True = False while True: ... On the other hand `1' will always be evaluated as a constant. Don't know, just guessing. Matteo On Jan/21, Andrea Crotti wrote: > I see sometimes in other people code "while 1" instead of "while True". > I think using True is more pythonic, but I wanted to check if there is > any difference in practice. > > So I tried to do the following, and the result is surprising. For what > I can see it looks like the interpreter can optimize away the 1 boolean > conversion while it doesn't with the True, the opposite of what I > supposed. > > Anyone can explain me why is that, or maybe is my conclusion wrong? > > def f1(): > while 1: > pass > > def f2(): > while True: > pass > > In [10]: dis.dis(f) > 2 0 SETUP_LOOP 3 (to 6) > > 3 >> 3 JUMP_ABSOLUTE 3 > >> 6 LOAD_CONST 0 (None) > 9 RETURN_VALUE > > In [9]: dis.dis(f1) > 2 0 SETUP_LOOP 10 (to 13) > >> 3 LOAD_GLOBAL 0 (True) > 6 POP_JUMP_IF_FALSE 12 > > 3 9 JUMP_ABSOLUTE 3 > >> 12 POP_BLOCK > >> 13 LOAD_CONST 0 (None) > 16 RETURN_VALUE > > -- > http://mail.python.org/mailman/listinfo/python-list > -- http://www.matteolandi.net