Path: csiph.com!usenet.pasdenom.info!aioe.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed3.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 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'python,': 0.02; 'argument': 0.05; 'interpreter': 0.05; "'',": 0.07; 'class,': 0.07; 'debugging': 0.07; 'correspond': 0.09; 'namespace': 0.09; 'url:github': 0.09; 'way:': 0.09; 'cc:addr:python-list': 0.11; '(class': 0.16; '(starting': 0.16; '(when': 0.16; '__new__': 0.16; 'bases,': 0.16; 'called,': 0.16; 'metaclass': 0.16; 'namespace.': 0.16; 'subclass': 0.16; 'thanks,': 0.17; 'wrote:': 0.18; 'all,': 0.19; 'trying': 0.19; '(but': 0.19; 'stack': 0.19; '>>>': 0.22; 'example': 0.22; 'import': 0.22; 'cc:addr:python.org': 0.22; 'header:User-Agent:1': 0.23; '(a)': 0.24; 'body,': 0.24; 'cc:2**0': 0.24; "i've": 0.25; 'this:': 0.26; 'header:In-Reply- To:1': 0.27; 'point': 0.28; 'function': 0.29; '(this': 0.29; 'skip:( 20': 0.30; "i'm": 0.30; 'url:mailman': 0.30; 'code': 0.31; '350': 0.31; 'inspect': 0.31; 'python2.7': 0.31; 'class': 0.32; 'url:python': 0.33; 'skip:_ 10': 0.34; 'classes': 0.35; 'received:google.com': 0.35; 'there': 0.35; 'keyword': 0.36; 'url:listinfo': 0.36; 'method': 0.36; 'charset:us-ascii': 0.36; 'url:org': 0.36; 'level': 0.37; 'does': 0.39; 'either': 0.39; 'skip:p 20': 0.39; 'url:mail': 0.40; 'how': 0.40; 'hope': 0.61; 'first': 0.61; 'content-disposition:inline': 0.62; 'side': 0.67; 'insight': 0.68; 'sound': 0.68; 'evaluate': 0.72; 'hoping': 0.75; 'pipeline': 0.91; 'subject:Class': 0.91; 'to:none': 0.92 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=date:from:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; bh=9fOxDfs9ZBEN0o/MEhKS2RbW3mId2CHBepXs/KRDYjE=; b=Wjo9KDgYCMvgkYeXaQ4LhtddESdiSPuMlQ9ZwQ0uGMm1UPnT7sD9bigQX0kn9fzXKs JLATiO/G2eGd58L+IVr8nsxahFSDJ2WTVfZxX+NVuABuuBjFkSWCdMMAwU3ohjItMoPe SxrCQ5ILGvkEMNTZQVOPwI5Hmd+BCZ5IVxtsrOgNAq5xhwAyat/WnrNzoLepnSZ4iMLP F9bOJvTWVhbPFeuAoesTIxKNwekb4XddkOsljLeyzigoMdsdOz00yXuT7z8qXV60iYVL EmR+Va4KRmEkpsd5ZtZKaBoYY/6n662W7yJ7Sj/CAx3KEdvrypj+v2kjZbDmsel9ri9X mTKg== X-Received: by 10.180.13.210 with SMTP id j18mr11693123wic.51.1382396264253; Mon, 21 Oct 2013 15:57:44 -0700 (PDT) Date: Mon, 21 Oct 2013 23:57:41 +0100 From: Marcin Szamotulski Cc: Python Subject: Re: Class construction References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 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: 1382396266 news.xs4all.nl 15906 [2001:888:2000:d::a6]:53924 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:57214 You can inspect the process in this way: >>> c = 'class A: pass' >>> code = compile(c, '', 'exec') >>> from dis import dis >>> dis(code) 1 0 LOAD_BUILD_CLASS 1 LOAD_CONST 0 (", line 1>) 4 LOAD_CONST 1 ('A') 7 MAKE_FUNCTION 0 10 LOAD_CONST 1 ('A') 13 CALL_FUNCTION 2 (2 positional, 0 keyword pair) 16 STORE_NAME 0 (A) 19 LOAD_CONST 2 (None) 22 RETURN_VALUE (this is in Python3.3, in Python2.7 the result will be different) Now you can check ceval.c (PyEval_EvalFrameEx function) what are the above opcode's doing. For example LOAD_BUILD_CLASS pushes the buildin function builtins.__build_class__ to the stack and then CALL_FUNCTION calls it. the c implementation of __build_class__ is in Python/bltinmodule.c (builtin___build_class__). Indeed this function will call the metaclass->tb_new `method` (but before it will also call the __prepare__ method on metaclass to get the namespace). The first argument on builtin__build_class__ is a function object which correspond to the class body, and it is evaluated in the class namespace. So the process (with some simplifications) goes like this: 1. get metaclass: meta 2. call meta.__prepare__ to get namespace (class __dict__) 3. evaluate the class body in the namespace 4. call meta with arguemnts: name, bases, namespace (when you instantiate any class in Python, metaclass is just a class, first its __new__ method is called, and then its __init__) All this is in builtin__build_class__. I hope it helps, Regards, Marcin On 08:08 Mon 21 Oct , Demian Brecht wrote: > Hi all, > > I'm trying to wrap my head around how classes are constructed at the > interpreter level (as a side effect of digging into metaclasses) and > I'm hoping to have my investigation either validated or ridiculed ;) > > The pipeline that I've figured through some gdb debugging (starting at > type_call): > > + type_call > + is there a metaclass for this object? > + return metaclass->tp_new > + roughly 350 LOC constructing the type > + is object is not a subclass of type? > + return object > + call obj->tp_init > > Does that sound correct? My C/gdb skills are horribly rusty at this > point so expert insight would help :) > > Thanks, > > -- > > Demian Brecht > http://demianbrecht.github.com > -- > https://mail.python.org/mailman/listinfo/python-list