1<html> 2<head> 3<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 4<title>How do I debug my Python extensions?</title> 5<link rel="stylesheet" href="../boostbook.css" type="text/css"> 6<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 7<link rel="home" href="../index.html" title="Boost.Python"> 8<link rel="up" href="../faq.html" title="Chapter 5. Frequently Asked Questions (FAQs)"> 9<link rel="prev" href="fatal_error_c1204_compiler_limit.html" title="fatal error C1204:Compiler limit:internal structure overflow"> 10<link rel="next" href="why_doesn_t_my_operator_work.html" title="Why doesn't my *= operator work?"> 11</head> 12<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 13<table cellpadding="2" width="100%"><tr><td valign="top"><img alt="" width="" height="" src="../images/boost.png"></td></tr></table> 14<hr> 15<div class="spirit-nav"> 16<a accesskey="p" href="fatal_error_c1204_compiler_limit.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../faq.html"><img src="../images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../images/home.png" alt="Home"></a><a accesskey="n" href="why_doesn_t_my_operator_work.html"><img src="../images/next.png" alt="Next"></a> 17</div> 18<div class="section"> 19<div class="titlepage"><div><div><h3 class="title"> 20<a name="faq.how_do_i_debug_my_python_extensi"></a><a class="link" href="how_do_i_debug_my_python_extensi.html" title="How do I debug my Python extensions?">How do I debug 21 my Python extensions?</a> 22</h3></div></div></div> 23<p> 24 Greg Burley gives the following answer for Unix GCC users: 25 </p> 26<div class="blockquote"><blockquote class="blockquote"> 27<p> 28 Once you have created a boost python extension for your c++ library or 29 class, you may need to debug the code. Afterall this is one of the reasons 30 for wrapping the library in python. An expected side-effect or benefit 31 of using BPL is that debugging should be isolated to the c++ library that 32 is under test, given that python code is minimal and boost::python either 33 works or it doesn't. (ie. While errors can occur when the wrapping method 34 is invalid, most errors are caught by the compiler ;-). 35 </p> 36<p> 37 The basic steps required to initiate a gdb session to debug a c++ library 38 via python are shown here. Note, however that you should start the gdb 39 session in the directory that contains your BPL my_ext.so module. 40 </p> 41<pre class="programlisting"><span class="special">(</span><span class="identifier">gdb</span><span class="special">)</span> <span class="identifier">target</span> <span class="identifier">exec</span> <span class="identifier">python</span> 42<span class="special">(</span><span class="identifier">gdb</span><span class="special">)</span> <span class="identifier">run</span> 43<span class="special">>>></span> <span class="identifier">from</span> <span class="identifier">my_ext</span> <span class="identifier">import</span> <span class="special">*</span> 44<span class="special">>>></span> <span class="special">[</span><span class="identifier">C</span><span class="special">-</span><span class="identifier">c</span><span class="special">]</span> 45<span class="special">(</span><span class="identifier">gdb</span><span class="special">)</span> <span class="keyword">break</span> <span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">MyBuggyFunction</span> 46<span class="special">(</span><span class="identifier">gdb</span><span class="special">)</span> <span class="identifier">cont</span> 47<span class="special">>>></span> <span class="identifier">pyobj</span> <span class="special">=</span> <span class="identifier">MyClass</span><span class="special">()</span> 48<span class="special">>>></span> <span class="identifier">pyobj</span><span class="special">.</span><span class="identifier">MyBuggyFunction</span><span class="special">()</span> 49<span class="identifier">Breakpoint</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">MyClass</span><span class="special">::</span><span class="identifier">MyBuggyFunction</span> <span class="special">...</span> 50<span class="identifier">Current</span> <span class="identifier">language</span><span class="special">:</span> <span class="keyword">auto</span><span class="special">;</span> <span class="identifier">currently</span> <span class="identifier">c</span><span class="special">++</span> 51<span class="special">(</span><span class="identifier">gdb</span><span class="special">)</span> <span class="keyword">do</span> <span class="identifier">debugging</span> <span class="identifier">stuff</span> 52</pre> 53</blockquote></div> 54<p> 55 Greg's approach works even better using Emacs' "gdb" command, since 56 it will show you each line of source as you step through it. 57 </p> 58<p> 59 On <span class="bold"><strong>Windows</strong></span>, my favorite debugging solution 60 is the debugger that comes with Microsoft Visual C++ 7. This debugger seems 61 to work with code generated by all versions of Microsoft and Metrowerks toolsets; 62 it's rock solid and "just works" without requiring any special 63 tricks from the user. 64 </p> 65<p> 66 Raoul Gough has provided the following for gdb on Windows: 67 </p> 68<div class="blockquote"><blockquote class="blockquote"> 69<p> 70 gdb support for Windows DLLs has improved lately, so it is now possible 71 to debug Python extensions using a few tricks. Firstly, you will need an 72 up-to-date gdb with support for minimal symbol extraction from a DLL. Any 73 gdb from version 6 onwards, or Cygwin gdb-20030214-1 and onwards should 74 do. A suitable release will have a section in the gdb.info file under Configuration 75 - Native - Cygwin Native - Non-debug DLL symbols. Refer to that info section 76 for more details of the procedures outlined here. 77 </p> 78<p> 79 Secondly, it seems necessary to set a breakpoint in the Python interpreter, 80 rather than using ^C to break execution. A good place to set this breakpoint 81 is PyOS_Readline, which will stop execution immediately before reading 82 each interactive Python command. You have to let Python start once under 83 the debugger, so that it loads its own DLL, before you can set the breakpoint: 84 </p> 85<pre class="programlisting"><span class="error">$</span> <span class="identifier">gdb</span> <span class="identifier">python</span> 86<span class="identifier">GNU</span> <span class="identifier">gdb</span> <span class="number">2003</span><span class="special">-</span><span class="number">09</span><span class="special">-</span><span class="number">02</span><span class="special">-</span><span class="identifier">cvs</span> <span class="special">(</span><span class="identifier">cygwin</span><span class="special">-</span><span class="identifier">special</span><span class="special">)</span> 87<span class="special">[...]</span> 88 89<span class="special">(</span><span class="identifier">gdb</span><span class="special">)</span> <span class="identifier">run</span> 90<span class="identifier">Starting</span> <span class="identifier">program</span><span class="special">:</span> <span class="special">/</span><span class="identifier">cygdrive</span><span class="special">/</span><span class="identifier">c</span><span class="special">/</span><span class="identifier">Python22</span><span class="special">/</span><span class="identifier">python</span><span class="special">.</span><span class="identifier">exe</span> 91<span class="identifier">Python</span> <span class="number">2.2</span><span class="special">.</span><span class="number">2</span> <span class="special">(#</span><span class="number">37</span><span class="special">,</span> <span class="identifier">Oct</span> <span class="number">14</span> <span class="number">2002</span><span class="special">,</span> <span class="number">17</span><span class="special">:</span><span class="number">02</span><span class="special">:</span><span class="number">34</span><span class="special">)</span> <span class="special">[</span><span class="identifier">MSC</span> <span class="number">32</span> <span class="identifier">bit</span> <span class="special">(</span><span class="identifier">Intel</span><span class="special">)]</span> <span class="identifier">on</span> <span class="identifier">win32</span> 92<span class="identifier">Type</span> <span class="string">"help"</span><span class="special">,</span> <span class="string">"copyright"</span><span class="special">,</span> <span class="string">"credits"</span> <span class="keyword">or</span> <span class="string">"license"</span> <span class="keyword">for</span> <span class="identifier">more</span> <span class="identifier">information</span><span class="special">.</span> 93<span class="special">>>></span> <span class="special">^</span><span class="identifier">Z</span> 94 95 96<span class="identifier">Program</span> <span class="identifier">exited</span> <span class="identifier">normally</span><span class="special">.</span> 97<span class="special">(</span><span class="identifier">gdb</span><span class="special">)</span> <span class="keyword">break</span> <span class="special">*&</span><span class="identifier">PyOS_Readline</span> 98<span class="identifier">Breakpoint</span> <span class="number">1</span> <span class="identifier">at</span> <span class="number">0x1e04eff0</span> 99<span class="special">(</span><span class="identifier">gdb</span><span class="special">)</span> <span class="identifier">run</span> 100<span class="identifier">Starting</span> <span class="identifier">program</span><span class="special">:</span> <span class="special">/</span><span class="identifier">cygdrive</span><span class="special">/</span><span class="identifier">c</span><span class="special">/</span><span class="identifier">Python22</span><span class="special">/</span><span class="identifier">python</span><span class="special">.</span><span class="identifier">exe</span> 101<span class="identifier">Python</span> <span class="number">2.2</span><span class="special">.</span><span class="number">2</span> <span class="special">(#</span><span class="number">37</span><span class="special">,</span> <span class="identifier">Oct</span> <span class="number">14</span> <span class="number">2002</span><span class="special">,</span> <span class="number">17</span><span class="special">:</span><span class="number">02</span><span class="special">:</span><span class="number">34</span><span class="special">)</span> <span class="special">[</span><span class="identifier">MSC</span> <span class="number">32</span> <span class="identifier">bit</span> <span class="special">(</span><span class="identifier">Intel</span><span class="special">)]</span> <span class="identifier">on</span> <span class="identifier">win32</span> 102<span class="identifier">Type</span> <span class="string">"help"</span><span class="special">,</span> <span class="string">"copyright"</span><span class="special">,</span> <span class="string">"credits"</span> <span class="keyword">or</span> <span class="string">"license"</span> <span class="keyword">for</span> <span class="identifier">more</span> <span class="identifier">information</span><span class="special">.</span> 103 104<span class="identifier">Breakpoint</span> <span class="number">1</span><span class="special">,</span> <span class="number">0x1e04eff0</span> <span class="identifier">in</span> <span class="identifier">python22</span><span class="special">!</span><span class="identifier">PyOS_Readline</span> <span class="special">()</span> 105 <span class="identifier">from</span> <span class="special">/</span><span class="identifier">cygdrive</span><span class="special">/</span><span class="identifier">c</span><span class="special">/</span><span class="identifier">WINNT</span><span class="special">/</span><span class="identifier">system32</span><span class="special">/</span><span class="identifier">python22</span><span class="special">.</span><span class="identifier">dll</span> 106<span class="special">(</span><span class="identifier">gdb</span><span class="special">)</span> <span class="identifier">cont</span> 107<span class="identifier">Continuing</span><span class="special">.</span> 108<span class="special">>>></span> <span class="identifier">from</span> <span class="identifier">my_ext</span> <span class="identifier">import</span> <span class="special">*</span> 109 110<span class="identifier">Breakpoint</span> <span class="number">1</span><span class="special">,</span> <span class="number">0x1e04eff0</span> <span class="identifier">in</span> <span class="identifier">python22</span><span class="special">!</span><span class="identifier">PyOS_Readline</span> <span class="special">()</span> 111 <span class="identifier">from</span> <span class="special">/</span><span class="identifier">cygdrive</span><span class="special">/</span><span class="identifier">c</span><span class="special">/</span><span class="identifier">WINNT</span><span class="special">/</span><span class="identifier">system32</span><span class="special">/</span><span class="identifier">python22</span><span class="special">.</span><span class="identifier">dll</span> 112<span class="special">(</span><span class="identifier">gdb</span><span class="special">)</span> <span class="special">#</span> <span class="identifier">my_ext</span> <span class="identifier">now</span> <span class="identifier">loaded</span> <span class="special">(</span><span class="identifier">with</span> <span class="identifier">any</span> <span class="identifier">debugging</span> <span class="identifier">symbols</span> <span class="identifier">it</span> <span class="identifier">contains</span><span class="special">)</span> 113</pre> 114</blockquote></div> 115<h3> 116<a name="faq.how_do_i_debug_my_python_extensi.h0"></a> 117 <span class="phrase"><a name="faq.how_do_i_debug_my_python_extensi.debugging_extensions_through_boo"></a></span><a class="link" href="how_do_i_debug_my_python_extensi.html#faq.how_do_i_debug_my_python_extensi.debugging_extensions_through_boo">Debugging 118 extensions through Boost.Build</a> 119 </h3> 120<p> 121 If you are launching your extension module tests with <a href="http://www.boost.org/build" target="_top">Boost.Build</a> 122 using the <code class="computeroutput"><span class="identifier">boost</span><span class="special">-</span><span class="identifier">python</span><span class="special">-</span><span class="identifier">runtest</span></code> rule, you can ask it to launch 123 your debugger for you by adding "--debugger=<span class="emphasis"><em>debugger</em></span>" 124 to your bjam command-line: 125 </p> 126<pre class="programlisting"><span class="identifier">bjam</span> <span class="special">-</span><span class="identifier">sTOOLS</span><span class="special">=</span><span class="identifier">vc7</span><span class="special">.</span><span class="number">1</span> <span class="string">"--debugger=devenv /debugexe"</span> <span class="identifier">test</span> 127<span class="identifier">bjam</span> <span class="special">-</span><span class="identifier">sTOOLS</span><span class="special">=</span><span class="identifier">gcc</span> <span class="special">-</span><span class="identifier">sPYTHON_LAUNCH</span><span class="special">=</span><span class="identifier">gdb</span> <span class="identifier">test</span> 128</pre> 129<p> 130 It can also be extremely useful to add the <code class="computeroutput"><span class="special">-</span><span class="identifier">d</span><span class="special">+</span><span class="number">2</span></code> 131 option when you run your test, because Boost.Build will then show you the 132 exact commands it uses to invoke it. This will invariably involve setting 133 up PYTHONPATH and other important environment variables such as LD_LIBRARY_PATH 134 which may be needed by your debugger in order to get things to work right. 135 </p> 136</div> 137<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 138<td align="left"></td> 139<td align="right"><div class="copyright-footer">Copyright © 2002-2015 David 140 Abrahams, Stefan Seefeld<p> 141 Distributed under the Boost Software License, Version 1.0. (See accompanying 142 file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) 143 </p> 144</div></td> 145</tr></table> 146<hr> 147<div class="spirit-nav"> 148<a accesskey="p" href="fatal_error_c1204_compiler_limit.html"><img src="../images/prev.png" alt="Prev"></a><a accesskey="u" href="../faq.html"><img src="../images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../images/home.png" alt="Home"></a><a accesskey="n" href="why_doesn_t_my_operator_work.html"><img src="../images/next.png" alt="Next"></a> 149</div> 150</body> 151</html> 152
