Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!newsfeed.xs4all.nl!newsfeed2.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 0.001 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'syntax': 0.03; 'debugging': 0.05; 'python': 0.09; '###': 0.09; 'ast': 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; 'resulting': 0.13; '(read': 0.16; 'received:80.91.229.3': 0.16; 'received:plane.gmane.org': 0.16; 'reedy': 0.16; 'written.': 0.16; 'wrote:': 0.17; 'have:': 0.17; 'instance': 0.17; 'instance,': 0.17; 'variables': 0.17; '(in': 0.18; 'jan': 0.18; 'module': 0.19; 'question.': 0.20; 'written': 0.20; "i'd": 0.22; 'example': 0.23; '15,': 0.23; 'statement': 0.23; 'header:In-Reply-To:1': 0.25; 'header:User-Agent:1': 0.26; '(which': 0.26; 'am,': 0.27; '(3)': 0.27; 'c++': 0.27; 'to?': 0.27; 'header:X-Complaints-To:1': 0.28; 'lines': 0.28; 'chris': 0.28; 'python).': 0.29; 'case,': 0.29; 'definition': 0.29; 'read,': 0.29; 'source': 0.29; 'function': 0.30; 'code': 0.31; '(2)': 0.32; 'to:addr:python-list': 0.33; 'another': 0.33; '(1)': 0.34; 'pm,': 0.35; 'received:org': 0.36; 'tool': 0.36; 'subject: (': 0.36; 'subject:: ': 0.38; 'to:addr:python.org': 0.39; 'header:Received:5': 0.40; 'your': 0.60; 'matter': 0.61; 'state.': 0.71; '2013': 0.84; 'etc,': 0.84; 'received:fios.verizon.net': 0.84; 'subject:read': 0.84; 'subject:write': 0.84; 'fibonacci': 0.91; 'write:': 0.91 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Terry Reedy Subject: Re: Finding the variables (read or write) Date: Mon, 14 Jan 2013 16:42:42 -0500 References: <46c8a630-de27-41dc-8b8b-1951ba747447@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:17.0) Gecko/17.0 Thunderbird/17.0 In-Reply-To: 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: 37 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1358199785 news.xs4all.nl 6923 [2001:888:2000:d::a6]:58484 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:36823 On 1/14/2013 4:28 PM, Chris Angelico wrote: > On Tue, Jan 15, 2013 at 6:48 AM, wrote: >> I'd like to develop a small debugging tool for python programs.In Dynamic Slicing How can I find the variables that are accessed in a statement? And find the type of access (read or write) for those variables (in Python). >> ### Write: A statement can change the program state. >> ### Read : A statement can read the program state . >> **For example in these 4 lines we have: >> (1) x = a+b => write{x} & read{a,b} >> (2) y=6 => write{y} & read{} >> (3) while(n>1) => write{} & read{n} >> (4) n=n-1 => write{n} & read{n} I would try compiling the source code to an ast (abstract syntax tree). See the ast module for how to do that and how to 'read' the resulting tree. > An interesting question. What's your definition of "variable"? For > instance, what is written and what is read by this statement: > > self.lst[2] += 4 > > Is "self.lst" considered a variable? (In C++ etc, this would be a > member function manipulating an instance variable.) Or is "self" the > variable? And in either case, was it written to? 'self' is read, 'lst' is written to. What about: > > self.lst.append(self.lst[-1]+self.lst[-2]) > > (which might collect Fibonacci numbers)? 'self' read, 'lst' read and written. Knowing that for non-builtins is another matter ;-). -- Terry Jan Reedy