Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!gegeweb.org!de-l.enfer-du-nord.net!feeder2.enfer-du-nord.net!newsfeed.eweka.nl!eweka.nl!feeder3.eweka.nl!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 0.005 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'definitions': 0.07; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:80.91.229.12': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'received:lo.gmane.org': 0.09; 'underlying': 0.09; 'am,': 0.12; 'enigma': 0.16; 'instances.': 0.16; 'kern': 0.16; 'metaclass': 0.16; 'metaclasses': 0.16; 'subject:classes': 0.16; 'wrote:': 0.18; 'trying': 0.21; 'maybe': 0.21; 'header:In-Reply-To:1': 0.22; 'statement': 0.23; 'defined': 0.24; 'fine': 0.24; 'code': 0.25; 'classes': 0.26; "i'm": 0.26; 'expect': 0.26; 'function': 0.27; 'van': 0.28; 'explicitly': 0.29; 'interpret': 0.29; 'weird': 0.29; 'class': 0.29; 'example': 0.29; 'url:library': 0.31; 'usually': 0.31; 'anyone': 0.31; 'header :User-Agent:1': 0.33; 'header:X-Complaints-To:1': 0.33; 'to:addr :python-list': 0.34; 'probably': 0.34; 'it.': 0.34; 'someone': 0.34; 'something': 0.35; 'unless': 0.35; 'url:python': 0.36; 'post': 0.36; 'explain': 0.36; 'minimal': 0.37; 'hello,': 0.37; 'doing': 0.38; 'using': 0.38; 'received:org': 0.38; 'some': 0.38; 'url:docs': 0.39; 'url:org': 0.39; 'help': 0.39; 'to:addr:python.org': 0.40; 'type': 0.61; 'world': 0.62; 'received:86': 0.63; 'our': 0.64; 'believe': 0.65; 'doing.': 0.73; 'why?': 0.77; 'eco': 0.91 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Robert Kern Subject: Re: pickling instances of metaclass generated classes Date: Thu, 29 Dec 2011 11:08:29 +0000 References: <2d221d0f-458e-4821-8786-f064b44b3125@p16g2000yqd.googlegroups.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Gmane-NNTP-Posting-Host: host86-145-112-31.range86-145.btcentralplus.com User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.7; rv:8.0) Gecko/20111105 Thunderbird/8.0 In-Reply-To: <2d221d0f-458e-4821-8786-f064b44b3125@p16g2000yqd.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: 35 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1325156924 news.xs4all.nl 6897 [2001:888:2000:d::a6]:56664 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:18165 On 12/29/11 9:55 AM, lars van gemerden wrote: > Hello, > > Can someone help me with the following: > > I am using metaclasses to make classes and these classes to make > instances. Now I want to use multiprocessing, which needs to pickle > these instances. > > Pickle cannot find the class definitions of the instances. I am trying > to add a line to the __new__ of the metaclass to add the new class > under the right name in the right module/place, so pickle can find > it. > > Is this the right approach? Can anyone explain to me where/how to add > these classes for pickle to find and maybe why? Can you post some code (preferably pared down to a minimal example that fails)? I'm not really clear on what you are doing. I would expect that a class defined by a class statement would usually work fine unless if the metaclass is doing something particularly weird to it. In any case, you can probably just explicitly register a reduction function for each type using copy_reg.pickle(): http://docs.python.org/library/copy_reg -- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco