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<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">faulthandler</span></code> — Dump the Python traceback</a><ul>
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<li><a class="reference internal" href="#dumping-the-traceback">Dumping the traceback</a></li>
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<li><a class="reference internal" href="#fault-handler-state">Fault handler state</a></li>
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<li><a class="reference internal" href="#dumping-the-tracebacks-after-a-timeout">Dumping the tracebacks after a timeout</a></li>
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<li><a class="reference internal" href="#dumping-the-traceback-on-a-user-signal">Dumping the traceback on a user signal</a></li>
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<section id="module-faulthandler">
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<span id="faulthandler-dump-the-python-traceback"></span><h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">faulthandler</span></code> — Dump the Python traceback<a class="headerlink" href="#module-faulthandler" title="Link to this heading">¶</a></h1>
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<div class="versionadded">
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<p><span class="versionmodified added">Added in version 3.3.</span></p>
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</div>
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<hr class="docutils" />
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<p>This module contains functions to dump Python tracebacks explicitly, on a fault,
|
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after a timeout, or on a user signal. Call <a class="reference internal" href="#faulthandler.enable" title="faulthandler.enable"><code class="xref py py-func docutils literal notranslate"><span class="pre">faulthandler.enable()</span></code></a> to
|
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install fault handlers for the <a class="reference internal" href="signal.html#signal.SIGSEGV" title="signal.SIGSEGV"><code class="xref py py-const docutils literal notranslate"><span class="pre">SIGSEGV</span></code></a>,
|
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<a class="reference internal" href="signal.html#signal.SIGFPE" title="signal.SIGFPE"><code class="xref py py-const docutils literal notranslate"><span class="pre">SIGFPE</span></code></a>, <a class="reference internal" href="signal.html#signal.SIGABRT" title="signal.SIGABRT"><code class="xref py py-const docutils literal notranslate"><span class="pre">SIGABRT</span></code></a>, <a class="reference internal" href="signal.html#signal.SIGBUS" title="signal.SIGBUS"><code class="xref py py-const docutils literal notranslate"><span class="pre">SIGBUS</span></code></a>, and
|
||
<a class="reference internal" href="signal.html#signal.SIGILL" title="signal.SIGILL"><code class="xref py py-const docutils literal notranslate"><span class="pre">SIGILL</span></code></a> signals. You can also
|
||
enable them at startup by setting the <span class="target" id="index-0"></span><a class="reference internal" href="../using/cmdline.html#envvar-PYTHONFAULTHANDLER"><code class="xref std std-envvar docutils literal notranslate"><span class="pre">PYTHONFAULTHANDLER</span></code></a> environment
|
||
variable or by using the <a class="reference internal" href="../using/cmdline.html#cmdoption-X"><code class="xref std std-option docutils literal notranslate"><span class="pre">-X</span></code></a> <code class="docutils literal notranslate"><span class="pre">faulthandler</span></code> command line option.</p>
|
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<p>The fault handler is compatible with system fault handlers like Apport or the
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Windows fault handler. The module uses an alternative stack for signal handlers
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if the <code class="xref c c-func docutils literal notranslate"><span class="pre">sigaltstack()</span></code> function is available. This allows it to dump the
|
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traceback even on a stack overflow.</p>
|
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<p>The fault handler is called on catastrophic cases and therefore can only use
|
||
signal-safe functions (e.g. it cannot allocate memory on the heap). Because of
|
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this limitation traceback dumping is minimal compared to normal Python
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tracebacks:</p>
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<ul class="simple">
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<li><p>Only ASCII is supported. The <code class="docutils literal notranslate"><span class="pre">backslashreplace</span></code> error handler is used on
|
||
encoding.</p></li>
|
||
<li><p>Each string is limited to 500 characters.</p></li>
|
||
<li><p>Only the filename, the function name and the line number are
|
||
displayed. (no source code)</p></li>
|
||
<li><p>It is limited to 100 frames and 100 threads.</p></li>
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<li><p>The order is reversed: the most recent call is shown first.</p></li>
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||
</ul>
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<p>By default, the Python traceback is written to <a class="reference internal" href="sys.html#sys.stderr" title="sys.stderr"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.stderr</span></code></a>. To see
|
||
tracebacks, applications must be run in the terminal. A log file can
|
||
alternatively be passed to <a class="reference internal" href="#faulthandler.enable" title="faulthandler.enable"><code class="xref py py-func docutils literal notranslate"><span class="pre">faulthandler.enable()</span></code></a>.</p>
|
||
<p>The module is implemented in C, so tracebacks can be dumped on a crash or when
|
||
Python is deadlocked.</p>
|
||
<p>The <a class="reference internal" href="devmode.html#devmode"><span class="std std-ref">Python Development Mode</span></a> calls <a class="reference internal" href="#faulthandler.enable" title="faulthandler.enable"><code class="xref py py-func docutils literal notranslate"><span class="pre">faulthandler.enable()</span></code></a>
|
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at Python startup.</p>
|
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<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<dl class="simple">
|
||
<dt>Module <a class="reference internal" href="pdb.html#module-pdb" title="pdb: The Python debugger for interactive interpreters."><code class="xref py py-mod docutils literal notranslate"><span class="pre">pdb</span></code></a></dt><dd><p>Interactive source code debugger for Python programs.</p>
|
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</dd>
|
||
<dt>Module <a class="reference internal" href="traceback.html#module-traceback" title="traceback: Print or retrieve a stack traceback."><code class="xref py py-mod docutils literal notranslate"><span class="pre">traceback</span></code></a></dt><dd><p>Standard interface to extract, format and print stack traces of Python programs.</p>
|
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</dd>
|
||
</dl>
|
||
</div>
|
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<section id="dumping-the-traceback">
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<h2>Dumping the traceback<a class="headerlink" href="#dumping-the-traceback" title="Link to this heading">¶</a></h2>
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<dl class="py function">
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<dt class="sig sig-object py" id="faulthandler.dump_traceback">
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<span class="sig-prename descclassname"><span class="pre">faulthandler.</span></span><span class="sig-name descname"><span class="pre">dump_traceback</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">file</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">sys.stderr</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">all_threads</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#faulthandler.dump_traceback" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Dump the tracebacks of all threads into <em>file</em>. If <em>all_threads</em> is
|
||
<code class="docutils literal notranslate"><span class="pre">False</span></code>, dump only the current thread.</p>
|
||
<div class="admonition seealso">
|
||
<p class="admonition-title">See also</p>
|
||
<p><a class="reference internal" href="traceback.html#traceback.print_tb" title="traceback.print_tb"><code class="xref py py-func docutils literal notranslate"><span class="pre">traceback.print_tb()</span></code></a>, which can be used to print a traceback object.</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.5: </span>Added support for passing file descriptor to this function.</p>
|
||
</div>
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</dd></dl>
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||
|
||
</section>
|
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<section id="fault-handler-state">
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||
<h2>Fault handler state<a class="headerlink" href="#fault-handler-state" title="Link to this heading">¶</a></h2>
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="faulthandler.enable">
|
||
<span class="sig-prename descclassname"><span class="pre">faulthandler.</span></span><span class="sig-name descname"><span class="pre">enable</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">file</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">sys.stderr</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">all_threads</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#faulthandler.enable" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Enable the fault handler: install handlers for the <a class="reference internal" href="signal.html#signal.SIGSEGV" title="signal.SIGSEGV"><code class="xref py py-const docutils literal notranslate"><span class="pre">SIGSEGV</span></code></a>,
|
||
<a class="reference internal" href="signal.html#signal.SIGFPE" title="signal.SIGFPE"><code class="xref py py-const docutils literal notranslate"><span class="pre">SIGFPE</span></code></a>, <a class="reference internal" href="signal.html#signal.SIGABRT" title="signal.SIGABRT"><code class="xref py py-const docutils literal notranslate"><span class="pre">SIGABRT</span></code></a>, <a class="reference internal" href="signal.html#signal.SIGBUS" title="signal.SIGBUS"><code class="xref py py-const docutils literal notranslate"><span class="pre">SIGBUS</span></code></a>
|
||
and <a class="reference internal" href="signal.html#signal.SIGILL" title="signal.SIGILL"><code class="xref py py-const docutils literal notranslate"><span class="pre">SIGILL</span></code></a>
|
||
signals to dump the Python traceback. If <em>all_threads</em> is <code class="docutils literal notranslate"><span class="pre">True</span></code>,
|
||
produce tracebacks for every running thread. Otherwise, dump only the current
|
||
thread.</p>
|
||
<p>The <em>file</em> must be kept open until the fault handler is disabled: see
|
||
<a class="reference internal" href="#faulthandler-fd"><span class="std std-ref">issue with file descriptors</span></a>.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.5: </span>Added support for passing file descriptor to this function.</p>
|
||
</div>
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||
<div class="versionchanged">
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||
<p><span class="versionmodified changed">Changed in version 3.6: </span>On Windows, a handler for Windows exception is also installed.</p>
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||
</div>
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||
<div class="versionchanged">
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<p><span class="versionmodified changed">Changed in version 3.10: </span>The dump now mentions if a garbage collector collection is running
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if <em>all_threads</em> is true.</p>
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||
</div>
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</dd></dl>
|
||
|
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<dl class="py function">
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||
<dt class="sig sig-object py" id="faulthandler.disable">
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||
<span class="sig-prename descclassname"><span class="pre">faulthandler.</span></span><span class="sig-name descname"><span class="pre">disable</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#faulthandler.disable" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Disable the fault handler: uninstall the signal handlers installed by
|
||
<a class="reference internal" href="#faulthandler.enable" title="faulthandler.enable"><code class="xref py py-func docutils literal notranslate"><span class="pre">enable()</span></code></a>.</p>
|
||
</dd></dl>
|
||
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="faulthandler.is_enabled">
|
||
<span class="sig-prename descclassname"><span class="pre">faulthandler.</span></span><span class="sig-name descname"><span class="pre">is_enabled</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#faulthandler.is_enabled" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Check if the fault handler is enabled.</p>
|
||
</dd></dl>
|
||
|
||
</section>
|
||
<section id="dumping-the-tracebacks-after-a-timeout">
|
||
<h2>Dumping the tracebacks after a timeout<a class="headerlink" href="#dumping-the-tracebacks-after-a-timeout" title="Link to this heading">¶</a></h2>
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="faulthandler.dump_traceback_later">
|
||
<span class="sig-prename descclassname"><span class="pre">faulthandler.</span></span><span class="sig-name descname"><span class="pre">dump_traceback_later</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">timeout</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">repeat</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">file</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">sys.stderr</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">exit</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#faulthandler.dump_traceback_later" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Dump the tracebacks of all threads, after a timeout of <em>timeout</em> seconds, or
|
||
every <em>timeout</em> seconds if <em>repeat</em> is <code class="docutils literal notranslate"><span class="pre">True</span></code>. If <em>exit</em> is <code class="docutils literal notranslate"><span class="pre">True</span></code>, call
|
||
<code class="xref c c-func docutils literal notranslate"><span class="pre">_exit()</span></code> with status=1 after dumping the tracebacks. (Note
|
||
<code class="xref c c-func docutils literal notranslate"><span class="pre">_exit()</span></code> exits the process immediately, which means it doesn’t do any
|
||
cleanup like flushing file buffers.) If the function is called twice, the new
|
||
call replaces previous parameters and resets the timeout. The timer has a
|
||
sub-second resolution.</p>
|
||
<p>The <em>file</em> must be kept open until the traceback is dumped or
|
||
<a class="reference internal" href="#faulthandler.cancel_dump_traceback_later" title="faulthandler.cancel_dump_traceback_later"><code class="xref py py-func docutils literal notranslate"><span class="pre">cancel_dump_traceback_later()</span></code></a> is called: see <a class="reference internal" href="#faulthandler-fd"><span class="std std-ref">issue with file
|
||
descriptors</span></a>.</p>
|
||
<p>This function is implemented using a watchdog thread.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.5: </span>Added support for passing file descriptor to this function.</p>
|
||
</div>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.7: </span>This function is now always available.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="faulthandler.cancel_dump_traceback_later">
|
||
<span class="sig-prename descclassname"><span class="pre">faulthandler.</span></span><span class="sig-name descname"><span class="pre">cancel_dump_traceback_later</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#faulthandler.cancel_dump_traceback_later" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Cancel the last call to <a class="reference internal" href="#faulthandler.dump_traceback_later" title="faulthandler.dump_traceback_later"><code class="xref py py-func docutils literal notranslate"><span class="pre">dump_traceback_later()</span></code></a>.</p>
|
||
</dd></dl>
|
||
|
||
</section>
|
||
<section id="dumping-the-traceback-on-a-user-signal">
|
||
<h2>Dumping the traceback on a user signal<a class="headerlink" href="#dumping-the-traceback-on-a-user-signal" title="Link to this heading">¶</a></h2>
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="faulthandler.register">
|
||
<span class="sig-prename descclassname"><span class="pre">faulthandler.</span></span><span class="sig-name descname"><span class="pre">register</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">signum</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">file</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">sys.stderr</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">all_threads</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">chain</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">False</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#faulthandler.register" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Register a user signal: install a handler for the <em>signum</em> signal to dump
|
||
the traceback of all threads, or of the current thread if <em>all_threads</em> is
|
||
<code class="docutils literal notranslate"><span class="pre">False</span></code>, into <em>file</em>. Call the previous handler if chain is <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>
|
||
<p>The <em>file</em> must be kept open until the signal is unregistered by
|
||
<a class="reference internal" href="#faulthandler.unregister" title="faulthandler.unregister"><code class="xref py py-func docutils literal notranslate"><span class="pre">unregister()</span></code></a>: see <a class="reference internal" href="#faulthandler-fd"><span class="std std-ref">issue with file descriptors</span></a>.</p>
|
||
<p>Not available on Windows.</p>
|
||
<div class="versionchanged">
|
||
<p><span class="versionmodified changed">Changed in version 3.5: </span>Added support for passing file descriptor to this function.</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="py function">
|
||
<dt class="sig sig-object py" id="faulthandler.unregister">
|
||
<span class="sig-prename descclassname"><span class="pre">faulthandler.</span></span><span class="sig-name descname"><span class="pre">unregister</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">signum</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#faulthandler.unregister" title="Link to this definition">¶</a></dt>
|
||
<dd><p>Unregister a user signal: uninstall the handler of the <em>signum</em> signal
|
||
installed by <a class="reference internal" href="#faulthandler.register" title="faulthandler.register"><code class="xref py py-func docutils literal notranslate"><span class="pre">register()</span></code></a>. Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the signal was registered,
|
||
<code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise.</p>
|
||
<p>Not available on Windows.</p>
|
||
</dd></dl>
|
||
|
||
</section>
|
||
<section id="issue-with-file-descriptors">
|
||
<span id="faulthandler-fd"></span><h2>Issue with file descriptors<a class="headerlink" href="#issue-with-file-descriptors" title="Link to this heading">¶</a></h2>
|
||
<p><a class="reference internal" href="#faulthandler.enable" title="faulthandler.enable"><code class="xref py py-func docutils literal notranslate"><span class="pre">enable()</span></code></a>, <a class="reference internal" href="#faulthandler.dump_traceback_later" title="faulthandler.dump_traceback_later"><code class="xref py py-func docutils literal notranslate"><span class="pre">dump_traceback_later()</span></code></a> and <a class="reference internal" href="#faulthandler.register" title="faulthandler.register"><code class="xref py py-func docutils literal notranslate"><span class="pre">register()</span></code></a> keep the
|
||
file descriptor of their <em>file</em> argument. If the file is closed and its file
|
||
descriptor is reused by a new file, or if <a class="reference internal" href="os.html#os.dup2" title="os.dup2"><code class="xref py py-func docutils literal notranslate"><span class="pre">os.dup2()</span></code></a> is used to replace
|
||
the file descriptor, the traceback will be written into a different file. Call
|
||
these functions again each time that the file is replaced.</p>
|
||
</section>
|
||
<section id="example">
|
||
<h2>Example<a class="headerlink" href="#example" title="Link to this heading">¶</a></h2>
|
||
<p>Example of a segmentation fault on Linux with and without enabling the fault
|
||
handler:</p>
|
||
<div class="highlight-shell-session notranslate"><div class="highlight"><pre><span></span><span class="gp">$ </span>python<span class="w"> </span>-c<span class="w"> </span><span class="s2">"import ctypes; ctypes.string_at(0)"</span>
|
||
<span class="go">Segmentation fault</span>
|
||
|
||
<span class="gp">$ </span>python<span class="w"> </span>-q<span class="w"> </span>-X<span class="w"> </span>faulthandler
|
||
<span class="go">>>> import ctypes</span>
|
||
<span class="go">>>> ctypes.string_at(0)</span>
|
||
<span class="go">Fatal Python error: Segmentation fault</span>
|
||
|
||
<span class="go">Current thread 0x00007fb899f39700 (most recent call first):</span>
|
||
<span class="go"> File "/home/python/cpython/Lib/ctypes/__init__.py", line 486 in string_at</span>
|
||
<span class="go"> File "<stdin>", line 1 in <module></span>
|
||
<span class="go">Segmentation fault</span>
|
||
</pre></div>
|
||
</div>
|
||
</section>
|
||
</section>
|
||
|
||
|
||
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|
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|
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|
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<h3><a href="../contents.html">Table of Contents</a></h3>
|
||
<ul>
|
||
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">faulthandler</span></code> — Dump the Python traceback</a><ul>
|
||
<li><a class="reference internal" href="#dumping-the-traceback">Dumping the traceback</a></li>
|
||
<li><a class="reference internal" href="#fault-handler-state">Fault handler state</a></li>
|
||
<li><a class="reference internal" href="#dumping-the-tracebacks-after-a-timeout">Dumping the tracebacks after a timeout</a></li>
|
||
<li><a class="reference internal" href="#dumping-the-traceback-on-a-user-signal">Dumping the traceback on a user signal</a></li>
|
||
<li><a class="reference internal" href="#issue-with-file-descriptors">Issue with file descriptors</a></li>
|
||
<li><a class="reference internal" href="#example">Example</a></li>
|
||
</ul>
|
||
</li>
|
||
</ul>
|
||
|
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|
||
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|
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||
title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">bdb</span></code> — Debugger framework</a></p>
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|
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<h4>Next topic</h4>
|
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Last updated on Apr 08, 2025 (14:33 UTC).
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