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: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'argument': 0.04; 'guido': 0.05; 'level,': 0.07; 'suppose': 0.07; 'variant': 0.07; 'python': 0.09; 'argument,': 0.09; 'modulo': 0.09; 'mutable': 0.09; 'parameter.': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'terry': 0.09; 'extension': 0.13; 'argument.': 0.16; 'binary,': 0.16; 'in- place': 0.16; 'message-id:@dough.gmane.org': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'reedy': 0.16; 'subject:skip:e 10': 0.16; 'third,': 0.16; 'wrote:': 0.17; 'documented': 0.17; 'jan': 0.18; '>>>': 0.18; 'code.': 0.20; 'bit': 0.21; 'latter': 0.22; 'struct': 0.22; 'subject:skip:i 10': 0.22; 'defined': 0.22; 'class.': 0.23; 'header:In-Reply-To:1': 0.25; 'header:User-Agent:1': 0.26; 'am,': 0.27; 'in.': 0.27; 'header:X-Complaints-To:1': 0.28; 'arguments.': 0.29; 'cases.': 0.29; 'coded': 0.29; 'consistency': 0.29; 'existence': 0.29; 'steven': 0.29; 'manual': 0.29; 'points': 0.29; 'probably': 0.29; "skip:' 10": 0.30; 'function': 0.30; 'implement': 0.32; 'true.': 0.33; 'to:addr:python-list': 0.33; 'operations': 0.33; 'version': 0.34; 'done': 0.34; 'third': 0.34; 'needed': 0.35; 'received:org': 0.36; 'really': 0.36; 'but': 0.36; 'method': 0.36; 'why': 0.37; '(for': 0.37; 'subject:: ': 0.38; 'mean': 0.38; 'planning': 0.38; 'sure': 0.38; 'to:addr:python.org': 0.39; 'where': 0.40; 'subject:-': 0.40; 'header:Received:5': 0.40; 'matter': 0.61; 'provide': 0.62; 'ever': 0.63; 'skip:n 10': 0.63; 'believe': 0.69; 'special': 0.73; 'power': 0.74; 'received:fios.verizon.net': 0.84; 'struct.': 0.84; 'mistake': 0.91 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Terry Reedy Subject: Re: in-place exponentiation incongruities Date: Sun, 12 Aug 2012 17:53:46 -0400 References: <502730da$0$29983$c3e8da3$5496439d@news.astraweb.com> <5bc4e58c-c587-46c3-93cc-95dea97d89e8@googlegroups.com> <50278d6b$0$29978$c3e8da3$5496439d@news.astraweb.com> <3118027d-0c13-425e-a874-4593b608cf45@googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Gmane-NNTP-Posting-Host: pool-173-75-251-66.phlapa.fios.verizon.net User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:14.0) Gecko/20120713 Thunderbird/14.0 In-Reply-To: <3118027d-0c13-425e-a874-4593b608cf45@googlegroups.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: 46 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1344808442 news.xs4all.nl 6842 [2001:888:2000:d::a6]:45518 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:26956 On 8/12/2012 7:55 AM, Giacomo Alzetta wrote: > What I mean is: when you implement a new type as a C extension you > have to provide special methods through the NumberMethods struct. In > this struct both the power and in-place power operations have three > arguments. I am not really sure why the latter is true. Probably 'consistency' at the special method level, with __pow__. As Steven points out, it is not needed to implement normal Python code. This is one area of Python where the design is a bit messy. I believe the very existence of __ipow__ is a matter of consistency than of known use cases. Guido was not sure which __ixxx__ would ever be needed (for mutable objects), so he just put them all in. At the Python level, both __pow__ and __ipow__ are also documented in the manual as having an optional, third, modulo parameter. __rpow__ is defined as binary, but that is a mistake >>> int.__rpow__(3, 5, 4) 1 > Now, suppose I implement the three argument variant of the > in-place power in a class. Are you actually planning to do this, or is this purely theoretical? > No user would be able to call my C > function with a non-None third argument, Not true. Whether the function is coded in Python or C cls.__ipow__(base, exp, mod) # or base.__ipow__(exp, mod) > while he would be able to > call the normal version with the third argument. That can also be done directly >>> int.__pow__(5, 3, 4) 1 -- Terry Jan Reedy