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<title>Debugging with GDB: Python Commands</title>
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<a name="Python-Commands"></a>
<div class="header">
<p>
Next: <a href="Python-API.html#Python-API" accesskey="n" rel="next">Python API</a>, Up: <a href="Python.html#Python" accesskey="u" rel="up">Python</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Python-Commands-1"></a>
<h4 class="subsection">23.3.1 Python Commands</h4>
<a name="index-python-commands"></a>
<a name="index-commands-to-access-python"></a>
<p><small>GDB</small> provides two commands for accessing the Python interpreter,
and one related setting:
</p>
<dl compact="compact">
<dd><a name="index-python_002dinteractive"></a>
<a name="index-pi"></a>
</dd>
<dt><code>python-interactive <span class="roman">[</span><var>command</var><span class="roman">]</span></code></dt>
<dt><code>pi <span class="roman">[</span><var>command</var><span class="roman">]</span></code></dt>
<dd><p>Without an argument, the <code>python-interactive</code> command can be used
to start an interactive Python prompt. To return to <small>GDB</small>,
type the <code>EOF</code> character (e.g., <kbd>Ctrl-D</kbd> on an empty prompt).
</p>
<p>Alternatively, a single-line Python command can be given as an
argument and evaluated. If the command is an expression, the result
will be printed; otherwise, nothing will be printed. For example:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) python-interactive 2 + 3
5
</pre></div>
<a name="index-python-1"></a>
<a name="index-py"></a>
</dd>
<dt><code>python <span class="roman">[</span><var>command</var><span class="roman">]</span></code></dt>
<dt><code>py <span class="roman">[</span><var>command</var><span class="roman">]</span></code></dt>
<dd><p>The <code>python</code> command can be used to evaluate Python code.
</p>
<p>If given an argument, the <code>python</code> command will evaluate the
argument as a Python command. For example:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) python print 23
23
</pre></div>
<p>If you do not provide an argument to <code>python</code>, it will act as a
multi-line command, like <code>define</code>. In this case, the Python
script is made up of subsequent command lines, given after the
<code>python</code> command. This command list is terminated using a line
containing <code>end</code>. For example:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) python
>print 23
>end
23
</pre></div>
<a name="set_005fpython_005fprint_005fstack"></a><a name="index-set-python-print_002dstack"></a>
</dd>
<dt><code>set python print-stack</code></dt>
<dd><p>By default, <small>GDB</small> will print only the message component of a
Python exception when an error occurs in a Python script. This can be
controlled using <code>set python print-stack</code>: if <code>full</code>, then
full Python stack printing is enabled; if <code>none</code>, then Python stack
and message printing is disabled; if <code>message</code>, the default, only
the message component of the error is printed.
</p>
<a name="index-set-python-ignore_002denvironment"></a>
</dd>
<dt><code>set python ignore-environment <span class="roman">[</span>on<span class="roman">|</span>off<span class="roman">]</span></code></dt>
<dd><p>By default this option is ‘<samp>off</samp>’, and, when <small>GDB</small>
initializes its internal Python interpreter, the Python interpreter
will check the environment for variables that will effect how it
behaves, for example <code>PYTHONHOME</code>, and
<code>PYTHONPATH</code><a name="DOCF19" href="#FOOT19"><sup>19</sup></a>.
</p>
<p>If this option is set to ‘<samp>on</samp>’ before Python is initialized then
Python will ignore all such environment variables. As Python is
initialized early during <small>GDB</small>’s startup process, then this
option must be placed into the early initialization file
(see <a href="Initialization-Files.html#Initialization-Files">Initialization Files</a>) to have the desired effect.
</p>
<p>This option is equivalent to passing <samp>-E</samp> to the real
<code>python</code> executable.
</p>
<a name="index-set-python-dont_002dwrite_002dbytecode"></a>
</dd>
<dt><code>set python dont-write-bytecode <span class="roman">[</span>auto<span class="roman">|</span>on<span class="roman">|</span>off<span class="roman">]</span></code></dt>
<dd><p>When this option is ‘<samp>off</samp>’, then, once <small>GDB</small> has
initialized the Python interpreter, the interpreter will byte-compile
any Python modules that it imports and write the byte code to disk in
<samp>.pyc</samp> files.
</p>
<p>If this option is set to ‘<samp>on</samp>’ before Python is initialized then
Python will no longer write the byte code to disk. As Python is
initialized early during <small>GDB</small>’s startup process, then this
option must be placed into the early initialization file
(see <a href="Initialization-Files.html#Initialization-Files">Initialization Files</a>) to have the desired effect.
</p>
<p>By default this option is set to ‘<samp>auto</samp>’. In this mode, provided
the <code>python ignore-environment</code> setting is ‘<samp>off</samp>’, the
environment variable <code>PYTHONDONTWRITEBYTECODE</code> is examined to see
if it should write out byte-code or not.
<code>PYTHONDONTWRITEBYTECODE</code> is considered to be off/disabled either
when set to the empty string or when the environment variable doesn’t
exist. All other settings, including those which don’t seem to make
sense, indicate that it’s on/enabled.
</p>
<p>This option is equivalent to passing <samp>-B</samp> to the real
<code>python</code> executable.
</p></dd>
</dl>
<p>It is also possible to execute a Python script from the <small>GDB</small>
interpreter:
</p>
<dl compact="compact">
<dt><code>source <samp>script-name</samp></code></dt>
<dd><p>The script name must end with ‘<samp>.py</samp>’ and <small>GDB</small> must be configured
to recognize the script language based on filename extension using
the <code>script-extension</code> setting. See <a href="Extending-GDB.html#Extending-GDB">Extending GDB</a>.
</p></dd>
</dl>
<p>The following commands are intended to help debug <small>GDB</small> itself:
</p>
<dl compact="compact">
<dd><a name="index-set-debug-py_002dbreakpoint"></a>
<a name="index-show-debug-py_002dbreakpoint"></a>
</dd>
<dt><code>set debug py-breakpoint on<span class="roman">|</span>off</code></dt>
<dt><code>show debug py-breakpoint</code></dt>
<dd><p>When ‘<samp>on</samp>’, <small>GDB</small> prints debug messages related to the
Python breakpoint API. This is ‘<samp>off</samp>’ by default.
</p>
<a name="index-set-debug-py_002dunwind"></a>
<a name="index-show-debug-py_002dunwind"></a>
</dd>
<dt><code>set debug py-unwind on<span class="roman">|</span>off</code></dt>
<dt><code>show debug py-unwind</code></dt>
<dd><p>When ‘<samp>on</samp>’, <small>GDB</small> prints debug messages related to the
Python unwinder API. This is ‘<samp>off</samp>’ by default.
</p></dd>
</dl>
<div class="footnote">
<hr>
<h4 class="footnotes-heading">Footnotes</h4>
<h3><a name="FOOT19" href="#DOCF19">(19)</a></h3>
<p>See the ENVIRONMENT VARIABLES section of
<code>man 1 python</code> for a comprehensive list.</p>
</div>
<hr>
<div class="header">
<p>
Next: <a href="Python-API.html#Python-API" accesskey="n" rel="next">Python API</a>, Up: <a href="Python.html#Python" accesskey="u" rel="up">Python</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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