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<li><a class="reference internal" href="#">Debugging C API extensions and CPython Internals with GDB</a><ul>
<li><a class="reference internal" href="#prerequisites">Prerequisites</a><ul>
<li><a class="reference internal" href="#setup-with-python-built-from-source">Setup with Python built from source</a></li>
<li><a class="reference internal" href="#setup-for-python-from-a-linux-distro">Setup for Python from a Linux distro</a></li>
</ul>
</li>
<li><a class="reference internal" href="#using-the-debug-build-and-development-mode">Using the Debug build and Development mode</a></li>
<li><a class="reference internal" href="#using-the-python-gdb-extension">Using the <code class="docutils literal notranslate"><span class="pre">python-gdb</span></code> extension</a><ul>
<li><a class="reference internal" href="#pretty-printers">Pretty-printers</a></li>
<li><a class="reference internal" href="#py-list"><code class="docutils literal notranslate"><span class="pre">py-list</span></code></a></li>
<li><a class="reference internal" href="#py-up-and-py-down"><code class="docutils literal notranslate"><span class="pre">py-up</span></code> and <code class="docutils literal notranslate"><span class="pre">py-down</span></code></a></li>
<li><a class="reference internal" href="#py-bt"><code class="docutils literal notranslate"><span class="pre">py-bt</span></code></a></li>
<li><a class="reference internal" href="#py-print"><code class="docutils literal notranslate"><span class="pre">py-print</span></code></a></li>
<li><a class="reference internal" href="#py-locals"><code class="docutils literal notranslate"><span class="pre">py-locals</span></code></a></li>
</ul>
</li>
<li><a class="reference internal" href="#use-with-gdb-commands">Use with GDB commands</a></li>
</ul>
</li>
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  <section id="debugging-c-api-extensions-and-cpython-internals-with-gdb">
<span id="gdb"></span><h1>Debugging C API extensions and CPython Internals with GDB<a class="headerlink" href="#debugging-c-api-extensions-and-cpython-internals-with-gdb" title="Link to this heading">¶</a></h1>
<p>This document explains how the Python GDB extension, <code class="docutils literal notranslate"><span class="pre">python-gdb.py</span></code>, can
be used with the GDB debugger to debug CPython extensions and the
CPython interpreter itself.</p>
<p>When debugging low-level problems such as crashes or deadlocks, a low-level
debugger, such as GDB, is useful to diagnose and correct the issue.
By default, GDB (or any of its front-ends) doesn’t support high-level
information specific to the CPython interpreter.</p>
<p>The <code class="docutils literal notranslate"><span class="pre">python-gdb.py</span></code> extension adds CPython interpreter information to GDB.
The extension helps introspect the stack of currently executing Python functions.
Given a Python object represented by a <span class="c-expr sig sig-inline c"><a class="reference internal" href="../c-api/structures.html#c.PyObject" title="PyObject"><span class="n">PyObject</span></a><span class="p">*</span></span> pointer,
the extension surfaces the type and value of the object.</p>
<p>Developers who are working on CPython extensions or tinkering with parts
of CPython that are written in C can use this document to learn how to use the
<code class="docutils literal notranslate"><span class="pre">python-gdb.py</span></code> extension with GDB.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>This document assumes that you are familiar with the basics of GDB and the
CPython C API. It consolidates guidance from the
<a class="reference external" href="https://devguide.python.org">devguide</a>  and the
<a class="reference external" href="https://wiki.python.org/moin/DebuggingWithGdb">Python wiki</a>.</p>
</div>
<section id="prerequisites">
<h2>Prerequisites<a class="headerlink" href="#prerequisites" title="Link to this heading">¶</a></h2>
<p>You need to have:</p>
<ul class="simple">
<li><p>GDB 7 or later. (For earlier versions of GDB, see <code class="docutils literal notranslate"><span class="pre">Misc/gdbinit</span></code> in the
sources of Python 3.11 or earlier.)</p></li>
<li><p>GDB-compatible debugging information for Python and any extension you are
debugging.</p></li>
<li><p>The <code class="docutils literal notranslate"><span class="pre">python-gdb.py</span></code> extension.</p></li>
</ul>
<p>The extension is built with Python, but might be distributed separately or
not at all. Below, we include tips for a few common systems as examples.
Note that even if the instructions match your system, they might be outdated.</p>
<section id="setup-with-python-built-from-source">
<h3>Setup with Python built from source<a class="headerlink" href="#setup-with-python-built-from-source" title="Link to this heading">¶</a></h3>
<p>When you build CPython from source, debugging information should be available,
and the build should add a <code class="docutils literal notranslate"><span class="pre">python-gdb.py</span></code> file to the root directory of
your repository.</p>
<p>To activate support, you must add the directory containing <code class="docutils literal notranslate"><span class="pre">python-gdb.py</span></code>
to GDB’s “auto-load-safe-path”.
If you haven’t done this, recent versions of GDB will print out a warning
with instructions on how to do this.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>If you do not see instructions for your version of GDB, put this in your
configuration file (<code class="docutils literal notranslate"><span class="pre">~/.gdbinit</span></code> or <code class="docutils literal notranslate"><span class="pre">~/.config/gdb/gdbinit</span></code>):</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>add-auto-load-safe-path /path/to/cpython
</pre></div>
</div>
<p>You can also add multiple paths, separated by <code class="docutils literal notranslate"><span class="pre">:</span></code>.</p>
</div>
</section>
<section id="setup-for-python-from-a-linux-distro">
<h3>Setup for Python from a Linux distro<a class="headerlink" href="#setup-for-python-from-a-linux-distro" title="Link to this heading">¶</a></h3>
<p>Most Linux systems provide debug information for the system Python
in a package called <code class="docutils literal notranslate"><span class="pre">python-debuginfo</span></code>, <code class="docutils literal notranslate"><span class="pre">python-dbg</span></code> or similar.
For example:</p>
<ul>
<li><p>Fedora:</p>
<blockquote>
<div><div class="highlight-shell notranslate"><div class="highlight"><pre><span></span>sudo<span class="w"> </span>dnf<span class="w"> </span>install<span class="w"> </span>gdb
sudo<span class="w"> </span>dnf<span class="w"> </span>debuginfo-install<span class="w"> </span>python3
</pre></div>
</div>
</div></blockquote>
</li>
<li><p>Ubuntu:</p>
<blockquote>
<div><div class="highlight-shell notranslate"><div class="highlight"><pre><span></span>sudo<span class="w"> </span>apt<span class="w"> </span>install<span class="w"> </span>gdb<span class="w"> </span>python3-dbg
</pre></div>
</div>
</div></blockquote>
</li>
</ul>
<p>On several recent Linux systems, GDB can download debugging symbols
automatically using <em>debuginfod</em>.
However, this will not install the <code class="docutils literal notranslate"><span class="pre">python-gdb.py</span></code> extension;
you generally do need to install the debug info package separately.</p>
</section>
</section>
<section id="using-the-debug-build-and-development-mode">
<h2>Using the Debug build and Development mode<a class="headerlink" href="#using-the-debug-build-and-development-mode" title="Link to this heading">¶</a></h2>
<p>For easier debugging, you might want to:</p>
<ul class="simple">
<li><p>Use a <a class="reference internal" href="../using/configure.html#debug-build"><span class="std std-ref">debug build</span></a> of Python. (When building from source,
use <code class="docutils literal notranslate"><span class="pre">configure</span> <span class="pre">--with-pydebug</span></code>. On Linux distros, install and run a package
like <code class="docutils literal notranslate"><span class="pre">python-debug</span></code> or <code class="docutils literal notranslate"><span class="pre">python-dbg</span></code>, if available.)</p></li>
<li><p>Use the runtime <a class="reference internal" href="../library/devmode.html#devmode"><span class="std std-ref">development mode</span></a> (<code class="docutils literal notranslate"><span class="pre">-X</span> <span class="pre">dev</span></code>).</p></li>
</ul>
<p>Both enable extra assertions and disable some optimizations.
Sometimes this hides the bug you are trying to find, but in most cases they
make the process easier.</p>
</section>
<section id="using-the-python-gdb-extension">
<h2>Using the <code class="docutils literal notranslate"><span class="pre">python-gdb</span></code> extension<a class="headerlink" href="#using-the-python-gdb-extension" title="Link to this heading">¶</a></h2>
<p>When the extension is loaded, it provides two main features:
pretty printers for Python values, and additional commands.</p>
<section id="pretty-printers">
<h3>Pretty-printers<a class="headerlink" href="#pretty-printers" title="Link to this heading">¶</a></h3>
<p>This is what a GDB backtrace looks like (truncated) when this extension is
enabled:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>#0  0x000000000041a6b1 in PyObject_Malloc (nbytes=Cannot access memory at address 0x7fffff7fefe8
) at Objects/obmalloc.c:748
#1  0x000000000041b7c0 in _PyObject_DebugMallocApi (id=111 &#39;o&#39;, nbytes=24) at Objects/obmalloc.c:1445
#2  0x000000000041b717 in _PyObject_DebugMalloc (nbytes=24) at Objects/obmalloc.c:1412
#3  0x000000000044060a in _PyUnicode_New (length=11) at Objects/unicodeobject.c:346
#4  0x00000000004466aa in PyUnicodeUCS2_DecodeUTF8Stateful (s=0x5c2b8d &quot;__lltrace__&quot;, size=11, errors=0x0, consumed=
    0x0) at Objects/unicodeobject.c:2531
#5  0x0000000000446647 in PyUnicodeUCS2_DecodeUTF8 (s=0x5c2b8d &quot;__lltrace__&quot;, size=11, errors=0x0)
    at Objects/unicodeobject.c:2495
#6  0x0000000000440d1b in PyUnicodeUCS2_FromStringAndSize (u=0x5c2b8d &quot;__lltrace__&quot;, size=11)
    at Objects/unicodeobject.c:551
#7  0x0000000000440d94 in PyUnicodeUCS2_FromString (u=0x5c2b8d &quot;__lltrace__&quot;) at Objects/unicodeobject.c:569
#8  0x0000000000584abd in PyDict_GetItemString (v=
    {&#39;Yuck&#39;: &lt;type at remote 0xad4730&gt;, &#39;__builtins__&#39;: &lt;module at remote 0x7ffff7fd5ee8&gt;, &#39;__file__&#39;: &#39;Lib/test/crashers/nasty_eq_vs_dict.py&#39;, &#39;__package__&#39;: None, &#39;y&#39;: &lt;Yuck(i=0) at remote 0xaacd80&gt;, &#39;dict&#39;: {0: 0, 1: 1, 2: 2, 3: 3}, &#39;__cached__&#39;: None, &#39;__name__&#39;: &#39;__main__&#39;, &#39;z&#39;: &lt;Yuck(i=0) at remote 0xaace60&gt;, &#39;__doc__&#39;: None}, key=
    0x5c2b8d &quot;__lltrace__&quot;) at Objects/dictobject.c:2171
</pre></div>
</div>
<p>Notice how the dictionary argument to <code class="docutils literal notranslate"><span class="pre">PyDict_GetItemString</span></code> is displayed
as its <code class="docutils literal notranslate"><span class="pre">repr()</span></code>, rather than an opaque <code class="docutils literal notranslate"><span class="pre">PyObject</span> <span class="pre">*</span></code> pointer.</p>
<p>The extension works by supplying a custom printing routine for values of type
<code class="docutils literal notranslate"><span class="pre">PyObject</span> <span class="pre">*</span></code>.  If you need to access lower-level details of an object, then
cast the value to a pointer of the appropriate type.  For example:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) p globals
$1 = {&#39;__builtins__&#39;: &lt;module at remote 0x7ffff7fb1868&gt;, &#39;__name__&#39;:
&#39;__main__&#39;, &#39;ctypes&#39;: &lt;module at remote 0x7ffff7f14360&gt;, &#39;__doc__&#39;: None,
&#39;__package__&#39;: None}

(gdb) p *(PyDictObject*)globals
$2 = {ob_refcnt = 3, ob_type = 0x3dbdf85820, ma_fill = 5, ma_used = 5,
ma_mask = 7, ma_table = 0x63d0f8, ma_lookup = 0x3dbdc7ea70
&lt;lookdict_string&gt;, ma_smalltable = {{me_hash = 7065186196740147912,
me_key = &#39;__builtins__&#39;, me_value = &lt;module at remote 0x7ffff7fb1868&gt;},
{me_hash = -368181376027291943, me_key = &#39;__name__&#39;,
me_value =&#39;__main__&#39;}, {me_hash = 0, me_key = 0x0, me_value = 0x0},
{me_hash = 0, me_key = 0x0, me_value = 0x0},
{me_hash = -9177857982131165996, me_key = &#39;ctypes&#39;,
me_value = &lt;module at remote 0x7ffff7f14360&gt;},
{me_hash = -8518757509529533123, me_key = &#39;__doc__&#39;, me_value = None},
{me_hash = 0, me_key = 0x0, me_value = 0x0}, {
  me_hash = 6614918939584953775, me_key = &#39;__package__&#39;, me_value = None}}}
</pre></div>
</div>
<p>Note that the pretty-printers do not actually call <code class="docutils literal notranslate"><span class="pre">repr()</span></code>.
For basic types, they try to match its result closely.</p>
<p>An area that can be confusing is that the custom printer for some types look a
lot like GDB’s built-in printer for standard types.  For example, the
pretty-printer for a Python <code class="docutils literal notranslate"><span class="pre">int</span></code> (<span class="c-expr sig sig-inline c"><a class="reference internal" href="../c-api/long.html#c.PyLongObject" title="PyLongObject"><span class="n">PyLongObject</span></a><span class="p">*</span></span>)
gives a representation that is not distinguishable from one of a
regular machine-level integer:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) p some_machine_integer
$3 = 42

(gdb) p some_python_integer
$4 = 42
</pre></div>
</div>
<p>The internal structure can be revealed with a cast to <span class="c-expr sig sig-inline c"><a class="reference internal" href="../c-api/long.html#c.PyLongObject" title="PyLongObject"><span class="n">PyLongObject</span></a><span class="p">*</span></span>:</p>
<blockquote>
<div><p>(gdb) p <em>(PyLongObject</em>)some_python_integer
$5 = {ob_base = {ob_base = {ob_refcnt = 8, ob_type = 0x3dad39f5e0}, ob_size = 1},
ob_digit = {42}}</p>
</div></blockquote>
<p>A similar confusion can arise with the <code class="docutils literal notranslate"><span class="pre">str</span></code> type, where the output looks a
lot like gdb’s built-in printer for <code class="docutils literal notranslate"><span class="pre">char</span> <span class="pre">*</span></code>:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) p ptr_to_python_str
$6 = &#39;__builtins__&#39;
</pre></div>
</div>
<p>The pretty-printer for <code class="docutils literal notranslate"><span class="pre">str</span></code> instances defaults to using single-quotes (as
does Python’s <code class="docutils literal notranslate"><span class="pre">repr</span></code> for strings) whereas the standard printer for <code class="docutils literal notranslate"><span class="pre">char</span> <span class="pre">*</span></code>
values uses double-quotes and contains a hexadecimal address:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) p ptr_to_char_star
$7 = 0x6d72c0 &quot;hello world&quot;
</pre></div>
</div>
<p>Again, the implementation details can be revealed with a cast to
<span class="c-expr sig sig-inline c"><a class="reference internal" href="../c-api/unicode.html#c.PyUnicodeObject" title="PyUnicodeObject"><span class="n">PyUnicodeObject</span></a><span class="p">*</span></span>:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) p *(PyUnicodeObject*)$6
$8 = {ob_base = {ob_refcnt = 33, ob_type = 0x3dad3a95a0}, length = 12,
str = 0x7ffff2128500, hash = 7065186196740147912, state = 1, defenc = 0x0}
</pre></div>
</div>
</section>
<section id="py-list">
<h3><code class="docutils literal notranslate"><span class="pre">py-list</span></code><a class="headerlink" href="#py-list" title="Link to this heading">¶</a></h3>
<blockquote>
<div><p>The extension adds a <code class="docutils literal notranslate"><span class="pre">py-list</span></code> command, which
lists the Python source code (if any) for the current frame in the selected
thread.  The current line is marked with a “&gt;”:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) py-list
 901        if options.profile:
 902            options.profile = False
 903            profile_me()
 904            return
 905
&gt;906        u = UI()
 907        if not u.quit:
 908            try:
 909                gtk.main()
 910            except KeyboardInterrupt:
 911                # properly quit on a keyboard interrupt...
</pre></div>
</div>
<p>Use <code class="docutils literal notranslate"><span class="pre">py-list</span> <span class="pre">START</span></code> to list at a different line number within the Python
source, and <code class="docutils literal notranslate"><span class="pre">py-list</span> <span class="pre">START,END</span></code> to list a specific range of lines within
the Python source.</p>
</div></blockquote>
</section>
<section id="py-up-and-py-down">
<h3><code class="docutils literal notranslate"><span class="pre">py-up</span></code> and <code class="docutils literal notranslate"><span class="pre">py-down</span></code><a class="headerlink" href="#py-up-and-py-down" title="Link to this heading">¶</a></h3>
<blockquote>
<div><p>The <code class="docutils literal notranslate"><span class="pre">py-up</span></code> and <code class="docutils literal notranslate"><span class="pre">py-down</span></code> commands are analogous to GDB’s regular <code class="docutils literal notranslate"><span class="pre">up</span></code>
and <code class="docutils literal notranslate"><span class="pre">down</span></code> commands, but try to move at the level of CPython frames, rather
than C frames.</p>
<p>GDB is not always able to read the relevant frame information, depending on
the optimization level with which CPython was compiled. Internally, the
commands look for C frames that are executing the default frame evaluation
function (that is, the core bytecode interpreter loop within CPython) and
look up the value of the related <code class="docutils literal notranslate"><span class="pre">PyFrameObject</span> <span class="pre">*</span></code>.</p>
<p>They emit the frame number (at the C level) within the thread.</p>
<p>For example:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) py-up
#37 Frame 0x9420b04, for file /usr/lib/python2.6/site-packages/
gnome_sudoku/main.py, line 906, in start_game ()
    u = UI()
(gdb) py-up
#40 Frame 0x948e82c, for file /usr/lib/python2.6/site-packages/
gnome_sudoku/gnome_sudoku.py, line 22, in start_game(main=&lt;module at remote 0xb771b7f4&gt;)
    main.start_game()
(gdb) py-up
Unable to find an older python frame
</pre></div>
</div>
<p>so we’re at the top of the Python stack.</p>
<p>The frame numbers correspond to those displayed by GDB’s standard
<code class="docutils literal notranslate"><span class="pre">backtrace</span></code> command.
The command skips C frames which are not executing Python code.</p>
<p>Going back down:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) py-down
#37 Frame 0x9420b04, for file /usr/lib/python2.6/site-packages/gnome_sudoku/main.py, line 906, in start_game ()
    u = UI()
(gdb) py-down
#34 (unable to read python frame information)
(gdb) py-down
#23 (unable to read python frame information)
(gdb) py-down
#19 (unable to read python frame information)
(gdb) py-down
#14 Frame 0x99262ac, for file /usr/lib/python2.6/site-packages/gnome_sudoku/game_selector.py, line 201, in run_swallowed_dialog (self=&lt;NewOrSavedGameSelector(new_game_model=&lt;gtk.ListStore at remote 0x98fab44&gt;, puzzle=None, saved_games=[{&#39;gsd.auto_fills&#39;: 0, &#39;tracking&#39;: {}, &#39;trackers&#39;: {}, &#39;notes&#39;: [], &#39;saved_at&#39;: 1270084485, &#39;game&#39;: &#39;7 8 0 0 0 0 0 5 6 0 0 9 0 8 0 1 0 0 0 4 6 0 0 0 0 7 0 6 5 0 0 0 4 7 9 2 0 0 0 9 0 1 0 0 0 3 9 7 6 0 0 0 1 8 0 6 0 0 0 0 2 8 0 0 0 5 0 4 0 6 0 0 2 1 0 0 0 0 0 4 5\n7 8 0 0 0 0 0 5 6 0 0 9 0 8 0 1 0 0 0 4 6 0 0 0 0 7 0 6 5 1 8 3 4 7 9 2 0 0 0 9 0 1 0 0 0 3 9 7 6 0 0 0 1 8 0 6 0 0 0 0 2 8 0 0 0 5 0 4 0 6 0 0 2 1 0 0 0 0 0 4 5&#39;, &#39;gsd.impossible_hints&#39;: 0, &#39;timer.__absolute_start_time__&#39;: &lt;float at remote 0x984b474&gt;, &#39;gsd.hints&#39;: 0, &#39;timer.active_time&#39;: &lt;float at remote 0x984b494&gt;, &#39;timer.total_time&#39;: &lt;float at remote 0x984b464&gt;}], dialog=&lt;gtk.Dialog at remote 0x98faaa4&gt;, saved_game_model=&lt;gtk.ListStore at remote 0x98fad24&gt;, sudoku_maker=&lt;SudokuMaker(terminated=False, played=[], batch_siz...(truncated)
            swallower.run_dialog(self.dialog)
(gdb) py-down
#11 Frame 0x9aead74, for file /usr/lib/python2.6/site-packages/gnome_sudoku/dialog_swallower.py, line 48, in run_dialog (self=&lt;SwappableArea(running=&lt;gtk.Dialog at remote 0x98faaa4&gt;, main_page=0) at remote 0x98fa6e4&gt;, d=&lt;gtk.Dialog at remote 0x98faaa4&gt;)
            gtk.main()
(gdb) py-down
#8 (unable to read python frame information)
(gdb) py-down
Unable to find a newer python frame
</pre></div>
</div>
<p>and we’re at the bottom of the Python stack.</p>
<p>Note that in Python 3.12 and newer, the same C stack frame can be used for
multiple Python stack frames. This means that <code class="docutils literal notranslate"><span class="pre">py-up</span></code> and <code class="docutils literal notranslate"><span class="pre">py-down</span></code>
may move multiple Python frames at once. For example:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) py-up
#6 Frame 0x7ffff7fb62b0, for file /tmp/rec.py, line 5, in recursive_function (n=0)
   time.sleep(5)
#6 Frame 0x7ffff7fb6240, for file /tmp/rec.py, line 7, in recursive_function (n=1)
   recursive_function(n-1)
#6 Frame 0x7ffff7fb61d0, for file /tmp/rec.py, line 7, in recursive_function (n=2)
   recursive_function(n-1)
#6 Frame 0x7ffff7fb6160, for file /tmp/rec.py, line 7, in recursive_function (n=3)
   recursive_function(n-1)
#6 Frame 0x7ffff7fb60f0, for file /tmp/rec.py, line 7, in recursive_function (n=4)
   recursive_function(n-1)
#6 Frame 0x7ffff7fb6080, for file /tmp/rec.py, line 7, in recursive_function (n=5)
   recursive_function(n-1)
#6 Frame 0x7ffff7fb6020, for file /tmp/rec.py, line 9, in &lt;module&gt; ()
   recursive_function(5)
(gdb) py-up
Unable to find an older python frame
</pre></div>
</div>
</div></blockquote>
</section>
<section id="py-bt">
<h3><code class="docutils literal notranslate"><span class="pre">py-bt</span></code><a class="headerlink" href="#py-bt" title="Link to this heading">¶</a></h3>
<blockquote>
<div><p>The <code class="docutils literal notranslate"><span class="pre">py-bt</span></code> command attempts to display a Python-level backtrace of the
current thread.</p>
<p>For example:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) py-bt
#8 (unable to read python frame information)
#11 Frame 0x9aead74, for file /usr/lib/python2.6/site-packages/gnome_sudoku/dialog_swallower.py, line 48, in run_dialog (self=&lt;SwappableArea(running=&lt;gtk.Dialog at remote 0x98faaa4&gt;, main_page=0) at remote 0x98fa6e4&gt;, d=&lt;gtk.Dialog at remote 0x98faaa4&gt;)
            gtk.main()
#14 Frame 0x99262ac, for file /usr/lib/python2.6/site-packages/gnome_sudoku/game_selector.py, line 201, in run_swallowed_dialog (self=&lt;NewOrSavedGameSelector(new_game_model=&lt;gtk.ListStore at remote 0x98fab44&gt;, puzzle=None, saved_games=[{&#39;gsd.auto_fills&#39;: 0, &#39;tracking&#39;: {}, &#39;trackers&#39;: {}, &#39;notes&#39;: [], &#39;saved_at&#39;: 1270084485, &#39;game&#39;: &#39;7 8 0 0 0 0 0 5 6 0 0 9 0 8 0 1 0 0 0 4 6 0 0 0 0 7 0 6 5 0 0 0 4 7 9 2 0 0 0 9 0 1 0 0 0 3 9 7 6 0 0 0 1 8 0 6 0 0 0 0 2 8 0 0 0 5 0 4 0 6 0 0 2 1 0 0 0 0 0 4 5\n7 8 0 0 0 0 0 5 6 0 0 9 0 8 0 1 0 0 0 4 6 0 0 0 0 7 0 6 5 1 8 3 4 7 9 2 0 0 0 9 0 1 0 0 0 3 9 7 6 0 0 0 1 8 0 6 0 0 0 0 2 8 0 0 0 5 0 4 0 6 0 0 2 1 0 0 0 0 0 4 5&#39;, &#39;gsd.impossible_hints&#39;: 0, &#39;timer.__absolute_start_time__&#39;: &lt;float at remote 0x984b474&gt;, &#39;gsd.hints&#39;: 0, &#39;timer.active_time&#39;: &lt;float at remote 0x984b494&gt;, &#39;timer.total_time&#39;: &lt;float at remote 0x984b464&gt;}], dialog=&lt;gtk.Dialog at remote 0x98faaa4&gt;, saved_game_model=&lt;gtk.ListStore at remote 0x98fad24&gt;, sudoku_maker=&lt;SudokuMaker(terminated=False, played=[], batch_siz...(truncated)
            swallower.run_dialog(self.dialog)
#19 (unable to read python frame information)
#23 (unable to read python frame information)
#34 (unable to read python frame information)
#37 Frame 0x9420b04, for file /usr/lib/python2.6/site-packages/gnome_sudoku/main.py, line 906, in start_game ()
    u = UI()
#40 Frame 0x948e82c, for file /usr/lib/python2.6/site-packages/gnome_sudoku/gnome_sudoku.py, line 22, in start_game (main=&lt;module at remote 0xb771b7f4&gt;)
    main.start_game()
</pre></div>
</div>
<p>The frame numbers correspond to those displayed by GDB’s standard
<code class="docutils literal notranslate"><span class="pre">backtrace</span></code> command.</p>
</div></blockquote>
</section>
<section id="py-print">
<h3><code class="docutils literal notranslate"><span class="pre">py-print</span></code><a class="headerlink" href="#py-print" title="Link to this heading">¶</a></h3>
<blockquote>
<div><p>The <code class="docutils literal notranslate"><span class="pre">py-print</span></code> command looks up a Python name and tries to print it.
It looks in locals within the current thread, then globals, then finally
builtins:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) py-print self
local &#39;self&#39; = &lt;SwappableArea(running=&lt;gtk.Dialog at remote 0x98faaa4&gt;,
main_page=0) at remote 0x98fa6e4&gt;
(gdb) py-print __name__
global &#39;__name__&#39; = &#39;gnome_sudoku.dialog_swallower&#39;
(gdb) py-print len
builtin &#39;len&#39; = &lt;built-in function len&gt;
(gdb) py-print scarlet_pimpernel
&#39;scarlet_pimpernel&#39; not found
</pre></div>
</div>
<p>If the current C frame corresponds to multiple Python frames, <code class="docutils literal notranslate"><span class="pre">py-print</span></code>
only considers the first one.</p>
</div></blockquote>
</section>
<section id="py-locals">
<h3><code class="docutils literal notranslate"><span class="pre">py-locals</span></code><a class="headerlink" href="#py-locals" title="Link to this heading">¶</a></h3>
<blockquote>
<div><p>The <code class="docutils literal notranslate"><span class="pre">py-locals</span></code> command looks up all Python locals within the current
Python frame in the selected thread, and prints their representations:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) py-locals
self = &lt;SwappableArea(running=&lt;gtk.Dialog at remote 0x98faaa4&gt;,
main_page=0) at remote 0x98fa6e4&gt;
d = &lt;gtk.Dialog at remote 0x98faaa4&gt;
</pre></div>
</div>
<p>If the current C frame corresponds to multiple Python frames, locals from
all of them will be shown:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) py-locals
Locals for recursive_function
n = 0
Locals for recursive_function
n = 1
Locals for recursive_function
n = 2
Locals for recursive_function
n = 3
Locals for recursive_function
n = 4
Locals for recursive_function
n = 5
Locals for &lt;module&gt;
</pre></div>
</div>
</div></blockquote>
</section>
</section>
<section id="use-with-gdb-commands">
<h2>Use with GDB commands<a class="headerlink" href="#use-with-gdb-commands" title="Link to this heading">¶</a></h2>
<p>The extension commands complement GDB’s built-in commands.
For example, you can use a frame numbers shown by <code class="docutils literal notranslate"><span class="pre">py-bt</span></code> with the <code class="docutils literal notranslate"><span class="pre">frame</span></code>
command to go a specific frame within the selected thread, like this:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) py-bt
(output snipped)
#68 Frame 0xaa4560, for file Lib/test/regrtest.py, line 1548, in &lt;module&gt; ()
        main()
(gdb) frame 68
#68 0x00000000004cd1e6 in PyEval_EvalFrameEx (f=Frame 0xaa4560, for file Lib/test/regrtest.py, line 1548, in &lt;module&gt; (), throwflag=0) at Python/ceval.c:2665
2665                            x = call_function(&amp;sp, oparg);
(gdb) py-list
1543        # Run the tests in a context manager that temporary changes the CWD to a
1544        # temporary and writable directory. If it&#39;s not possible to create or
1545        # change the CWD, the original CWD will be used. The original CWD is
1546        # available from test_support.SAVEDCWD.
1547        with test_support.temp_cwd(TESTCWD, quiet=True):
&gt;1548            main()
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">info</span> <span class="pre">threads</span></code> command will give you a list of the threads within the
process, and you can use the <code class="docutils literal notranslate"><span class="pre">thread</span></code> command to select a different one:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) info threads
  105 Thread 0x7fffefa18710 (LWP 10260)  sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:86
  104 Thread 0x7fffdf5fe710 (LWP 10259)  sem_wait () at ../nptl/sysdeps/unix/sysv/linux/x86_64/sem_wait.S:86
* 1 Thread 0x7ffff7fe2700 (LWP 10145)  0x00000038e46d73e3 in select () at ../sysdeps/unix/syscall-template.S:82
</pre></div>
</div>
<p>You can use <code class="docutils literal notranslate"><span class="pre">thread</span> <span class="pre">apply</span> <span class="pre">all</span> <span class="pre">COMMAND</span></code> or (<code class="docutils literal notranslate"><span class="pre">t</span> <span class="pre">a</span> <span class="pre">a</span> <span class="pre">COMMAND</span></code> for short) to run
a command on all threads.  With <code class="docutils literal notranslate"><span class="pre">py-bt</span></code>, this lets you see what every
thread is doing at the Python level:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>(gdb) t a a py-bt

Thread 105 (Thread 0x7fffefa18710 (LWP 10260)):
#5 Frame 0x7fffd00019d0, for file /home/david/coding/python-svn/Lib/threading.py, line 155, in _acquire_restore (self=&lt;_RLock(_Verbose__verbose=False, _RLock__owner=140737354016512, _RLock__block=&lt;thread.lock at remote 0x858770&gt;, _RLock__count=1) at remote 0xd7ff40&gt;, count_owner=(1, 140737213728528), count=1, owner=140737213728528)
        self.__block.acquire()
#8 Frame 0x7fffac001640, for file /home/david/coding/python-svn/Lib/threading.py, line 269, in wait (self=&lt;_Condition(_Condition__lock=&lt;_RLock(_Verbose__verbose=False, _RLock__owner=140737354016512, _RLock__block=&lt;thread.lock at remote 0x858770&gt;, _RLock__count=1) at remote 0xd7ff40&gt;, acquire=&lt;instancemethod at remote 0xd80260&gt;, _is_owned=&lt;instancemethod at remote 0xd80160&gt;, _release_save=&lt;instancemethod at remote 0xd803e0&gt;, release=&lt;instancemethod at remote 0xd802e0&gt;, _acquire_restore=&lt;instancemethod at remote 0xd7ee60&gt;, _Verbose__verbose=False, _Condition__waiters=[]) at remote 0xd7fd10&gt;, timeout=None, waiter=&lt;thread.lock at remote 0x858a90&gt;, saved_state=(1, 140737213728528))
            self._acquire_restore(saved_state)
#12 Frame 0x7fffb8001a10, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 348, in f ()
            cond.wait()
#16 Frame 0x7fffb8001c40, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 37, in task (tid=140737213728528)
                f()

Thread 104 (Thread 0x7fffdf5fe710 (LWP 10259)):
#5 Frame 0x7fffe4001580, for file /home/david/coding/python-svn/Lib/threading.py, line 155, in _acquire_restore (self=&lt;_RLock(_Verbose__verbose=False, _RLock__owner=140737354016512, _RLock__block=&lt;thread.lock at remote 0x858770&gt;, _RLock__count=1) at remote 0xd7ff40&gt;, count_owner=(1, 140736940992272), count=1, owner=140736940992272)
        self.__block.acquire()
#8 Frame 0x7fffc8002090, for file /home/david/coding/python-svn/Lib/threading.py, line 269, in wait (self=&lt;_Condition(_Condition__lock=&lt;_RLock(_Verbose__verbose=False, _RLock__owner=140737354016512, _RLock__block=&lt;thread.lock at remote 0x858770&gt;, _RLock__count=1) at remote 0xd7ff40&gt;, acquire=&lt;instancemethod at remote 0xd80260&gt;, _is_owned=&lt;instancemethod at remote 0xd80160&gt;, _release_save=&lt;instancemethod at remote 0xd803e0&gt;, release=&lt;instancemethod at remote 0xd802e0&gt;, _acquire_restore=&lt;instancemethod at remote 0xd7ee60&gt;, _Verbose__verbose=False, _Condition__waiters=[]) at remote 0xd7fd10&gt;, timeout=None, waiter=&lt;thread.lock at remote 0x858860&gt;, saved_state=(1, 140736940992272))
            self._acquire_restore(saved_state)
#12 Frame 0x7fffac001c90, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 348, in f ()
            cond.wait()
#16 Frame 0x7fffac0011c0, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 37, in task (tid=140736940992272)
                f()

Thread 1 (Thread 0x7ffff7fe2700 (LWP 10145)):
#5 Frame 0xcb5380, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 16, in _wait ()
    time.sleep(0.01)
#8 Frame 0x7fffd00024a0, for file /home/david/coding/python-svn/Lib/test/lock_tests.py, line 378, in _check_notify (self=&lt;ConditionTests(_testMethodName=&#39;test_notify&#39;, _resultForDoCleanups=&lt;TestResult(_original_stdout=&lt;cStringIO.StringO at remote 0xc191e0&gt;, skipped=[], _mirrorOutput=False, testsRun=39, buffer=False, _original_stderr=&lt;file at remote 0x7ffff7fc6340&gt;, _stdout_buffer=&lt;cStringIO.StringO at remote 0xc9c7f8&gt;, _stderr_buffer=&lt;cStringIO.StringO at remote 0xc9c790&gt;, _moduleSetUpFailed=False, expectedFailures=[], errors=[], _previousTestClass=&lt;type at remote 0x928310&gt;, unexpectedSuccesses=[], failures=[], shouldStop=False, failfast=False) at remote 0xc185a0&gt;, _threads=(0,), _cleanups=[], _type_equality_funcs={&lt;type at remote 0x7eba00&gt;: &lt;instancemethod at remote 0xd750e0&gt;, &lt;type at remote 0x7e7820&gt;: &lt;instancemethod at remote 0xd75160&gt;, &lt;type at remote 0x7e30e0&gt;: &lt;instancemethod at remote 0xd75060&gt;, &lt;type at remote 0x7e7d20&gt;: &lt;instancemethod at remote 0xd751e0&gt;, &lt;type at remote 0x7f19e0...(truncated)
        _wait()
</pre></div>
</div>
</section>
</section>


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  <div>
    <h3><a href="../contents.html">Table of Contents</a></h3>
    <ul>
<li><a class="reference internal" href="#">Debugging C API extensions and CPython Internals with GDB</a><ul>
<li><a class="reference internal" href="#prerequisites">Prerequisites</a><ul>
<li><a class="reference internal" href="#setup-with-python-built-from-source">Setup with Python built from source</a></li>
<li><a class="reference internal" href="#setup-for-python-from-a-linux-distro">Setup for Python from a Linux distro</a></li>
</ul>
</li>
<li><a class="reference internal" href="#using-the-debug-build-and-development-mode">Using the Debug build and Development mode</a></li>
<li><a class="reference internal" href="#using-the-python-gdb-extension">Using the <code class="docutils literal notranslate"><span class="pre">python-gdb</span></code> extension</a><ul>
<li><a class="reference internal" href="#pretty-printers">Pretty-printers</a></li>
<li><a class="reference internal" href="#py-list"><code class="docutils literal notranslate"><span class="pre">py-list</span></code></a></li>
<li><a class="reference internal" href="#py-up-and-py-down"><code class="docutils literal notranslate"><span class="pre">py-up</span></code> and <code class="docutils literal notranslate"><span class="pre">py-down</span></code></a></li>
<li><a class="reference internal" href="#py-bt"><code class="docutils literal notranslate"><span class="pre">py-bt</span></code></a></li>
<li><a class="reference internal" href="#py-print"><code class="docutils literal notranslate"><span class="pre">py-print</span></code></a></li>
<li><a class="reference internal" href="#py-locals"><code class="docutils literal notranslate"><span class="pre">py-locals</span></code></a></li>
</ul>
</li>
<li><a class="reference internal" href="#use-with-gdb-commands">Use with GDB commands</a></li>
</ul>
</li>
</ul>

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