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<title>traceback — Print or retrieve a stack traceback &#8212; Python 3.7.4 documentation</title>
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<div class="section" id="module-traceback">
<span id="traceback-print-or-retrieve-a-stack-traceback"></span><h1><a class="reference internal" href="#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> — Print or retrieve a stack traceback<a class="headerlink" href="#module-traceback" title="Permalink to this headline"></a></h1>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/traceback.py">Lib/traceback.py</a></p>
<hr class="docutils" />
<p>This module provides a standard interface to extract, format and print stack
traces of Python programs. It exactly mimics the behavior of the Python
interpreter when it prints a stack trace. This is useful when you want to print
stack traces under program control, such as in a “wrapper” around the
interpreter.</p>
<p id="index-0">The module uses traceback objects — this is the object type that is stored in
the <a class="reference internal" href="sys.html#sys.last_traceback" title="sys.last_traceback"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.last_traceback</span></code></a> variable and returned as the third item from
<a class="reference internal" href="sys.html#sys.exc_info" title="sys.exc_info"><code class="xref py py-func docutils literal notranslate"><span class="pre">sys.exc_info()</span></code></a>.</p>
<p>The module defines the following functions:</p>
<dl class="function">
<dt id="traceback.print_tb">
<code class="descclassname">traceback.</code><code class="descname">print_tb</code><span class="sig-paren">(</span><em>tb</em>, <em>limit=None</em>, <em>file=None</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.print_tb" title="Permalink to this definition"></a></dt>
<dd><p>Print up to <em>limit</em> stack trace entries from traceback object <em>tb</em> (starting
from the caller’s frame) if <em>limit</em> is positive. Otherwise, print the last
<code class="docutils literal notranslate"><span class="pre">abs(limit)</span></code> entries. If <em>limit</em> is omitted or <code class="docutils literal notranslate"><span class="pre">None</span></code>, all entries are
printed. If <em>file</em> is omitted or <code class="docutils literal notranslate"><span class="pre">None</span></code>, the output goes to
<code class="docutils literal notranslate"><span class="pre">sys.stderr</span></code>; otherwise it should be an open file or file-like object to
receive the output.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.5: </span>Added negative <em>limit</em> support.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="traceback.print_exception">
<code class="descclassname">traceback.</code><code class="descname">print_exception</code><span class="sig-paren">(</span><em>etype</em>, <em>value</em>, <em>tb</em>, <em>limit=None</em>, <em>file=None</em>, <em>chain=True</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.print_exception" title="Permalink to this definition"></a></dt>
<dd><p>Print exception information and stack trace entries from traceback object
<em>tb</em> to <em>file</em>. This differs from <a class="reference internal" href="#traceback.print_tb" title="traceback.print_tb"><code class="xref py py-func docutils literal notranslate"><span class="pre">print_tb()</span></code></a> in the following
ways:</p>
<ul class="simple">
<li><p>if <em>tb</em> is not <code class="docutils literal notranslate"><span class="pre">None</span></code>, it prints a header <code class="docutils literal notranslate"><span class="pre">Traceback</span> <span class="pre">(most</span> <span class="pre">recent</span>
<span class="pre">call</span> <span class="pre">last):</span></code></p></li>
<li><p>it prints the exception <em>etype</em> and <em>value</em> after the stack trace</p></li>
</ul>
<ul class="simple" id="index-1">
<li><p>if <em>type(value)</em> is <a class="reference internal" href="exceptions.html#SyntaxError" title="SyntaxError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SyntaxError</span></code></a> and <em>value</em> has the appropriate
format, it prints the line where the syntax error occurred with a caret
indicating the approximate position of the error.</p></li>
</ul>
<p>The optional <em>limit</em> argument has the same meaning as for <a class="reference internal" href="#traceback.print_tb" title="traceback.print_tb"><code class="xref py py-func docutils literal notranslate"><span class="pre">print_tb()</span></code></a>.
If <em>chain</em> is true (the default), then chained exceptions (the
<code class="xref py py-attr docutils literal notranslate"><span class="pre">__cause__</span></code> or <code class="xref py py-attr docutils literal notranslate"><span class="pre">__context__</span></code> attributes of the exception) will be
printed as well, like the interpreter itself does when printing an unhandled
exception.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.5: </span>The <em>etype</em> argument is ignored and inferred from the type of <em>value</em>.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="traceback.print_exc">
<code class="descclassname">traceback.</code><code class="descname">print_exc</code><span class="sig-paren">(</span><em>limit=None</em>, <em>file=None</em>, <em>chain=True</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.print_exc" title="Permalink to this definition"></a></dt>
<dd><p>This is a shorthand for <code class="docutils literal notranslate"><span class="pre">print_exception(*sys.exc_info(),</span> <span class="pre">limit,</span> <span class="pre">file,</span>
<span class="pre">chain)</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="traceback.print_last">
<code class="descclassname">traceback.</code><code class="descname">print_last</code><span class="sig-paren">(</span><em>limit=None</em>, <em>file=None</em>, <em>chain=True</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.print_last" title="Permalink to this definition"></a></dt>
<dd><p>This is a shorthand for <code class="docutils literal notranslate"><span class="pre">print_exception(sys.last_type,</span> <span class="pre">sys.last_value,</span>
<span class="pre">sys.last_traceback,</span> <span class="pre">limit,</span> <span class="pre">file,</span> <span class="pre">chain)</span></code>. In general it will work only
after an exception has reached an interactive prompt (see
<a class="reference internal" href="sys.html#sys.last_type" title="sys.last_type"><code class="xref py py-data docutils literal notranslate"><span class="pre">sys.last_type</span></code></a>).</p>
</dd></dl>
<dl class="function">
<dt id="traceback.print_stack">
<code class="descclassname">traceback.</code><code class="descname">print_stack</code><span class="sig-paren">(</span><em>f=None</em>, <em>limit=None</em>, <em>file=None</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.print_stack" title="Permalink to this definition"></a></dt>
<dd><p>Print up to <em>limit</em> stack trace entries (starting from the invocation
point) if <em>limit</em> is positive. Otherwise, print the last <code class="docutils literal notranslate"><span class="pre">abs(limit)</span></code>
entries. If <em>limit</em> is omitted or <code class="docutils literal notranslate"><span class="pre">None</span></code>, all entries are printed.
The optional <em>f</em> argument can be used to specify an alternate stack frame
to start. The optional <em>file</em> argument has the same meaning as for
<a class="reference internal" href="#traceback.print_tb" title="traceback.print_tb"><code class="xref py py-func docutils literal notranslate"><span class="pre">print_tb()</span></code></a>.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.5: </span>Added negative <em>limit</em> support.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="traceback.extract_tb">
<code class="descclassname">traceback.</code><code class="descname">extract_tb</code><span class="sig-paren">(</span><em>tb</em>, <em>limit=None</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.extract_tb" title="Permalink to this definition"></a></dt>
<dd><p>Return a <a class="reference internal" href="#traceback.StackSummary" title="traceback.StackSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">StackSummary</span></code></a> object representing a list of “pre-processed”
stack trace entries extracted from the traceback object <em>tb</em>. It is useful
for alternate formatting of stack traces. The optional <em>limit</em> argument has
the same meaning as for <a class="reference internal" href="#traceback.print_tb" title="traceback.print_tb"><code class="xref py py-func docutils literal notranslate"><span class="pre">print_tb()</span></code></a>. A “pre-processed” stack trace
entry is a <a class="reference internal" href="#traceback.FrameSummary" title="traceback.FrameSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">FrameSummary</span></code></a> object containing attributes
<code class="xref py py-attr docutils literal notranslate"><span class="pre">filename</span></code>, <code class="xref py py-attr docutils literal notranslate"><span class="pre">lineno</span></code>,
<code class="xref py py-attr docutils literal notranslate"><span class="pre">name</span></code>, and <code class="xref py py-attr docutils literal notranslate"><span class="pre">line</span></code> representing the
information that is usually printed for a stack trace. The
<code class="xref py py-attr docutils literal notranslate"><span class="pre">line</span></code> is a string with leading and trailing
whitespace stripped; if the source is not available it is <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="traceback.extract_stack">
<code class="descclassname">traceback.</code><code class="descname">extract_stack</code><span class="sig-paren">(</span><em>f=None</em>, <em>limit=None</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.extract_stack" title="Permalink to this definition"></a></dt>
<dd><p>Extract the raw traceback from the current stack frame. The return value has
the same format as for <a class="reference internal" href="#traceback.extract_tb" title="traceback.extract_tb"><code class="xref py py-func docutils literal notranslate"><span class="pre">extract_tb()</span></code></a>. The optional <em>f</em> and <em>limit</em>
arguments have the same meaning as for <a class="reference internal" href="#traceback.print_stack" title="traceback.print_stack"><code class="xref py py-func docutils literal notranslate"><span class="pre">print_stack()</span></code></a>.</p>
</dd></dl>
<dl class="function">
<dt id="traceback.format_list">
<code class="descclassname">traceback.</code><code class="descname">format_list</code><span class="sig-paren">(</span><em>extracted_list</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.format_list" title="Permalink to this definition"></a></dt>
<dd><p>Given a list of tuples or <a class="reference internal" href="#traceback.FrameSummary" title="traceback.FrameSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">FrameSummary</span></code></a> objects as returned by
<a class="reference internal" href="#traceback.extract_tb" title="traceback.extract_tb"><code class="xref py py-func docutils literal notranslate"><span class="pre">extract_tb()</span></code></a> or <a class="reference internal" href="#traceback.extract_stack" title="traceback.extract_stack"><code class="xref py py-func docutils literal notranslate"><span class="pre">extract_stack()</span></code></a>, return a list of strings ready
for printing. Each string in the resulting list corresponds to the item with
the same index in the argument list. Each string ends in a newline; the
strings may contain internal newlines as well, for those items whose source
text line is not <code class="docutils literal notranslate"><span class="pre">None</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="traceback.format_exception_only">
<code class="descclassname">traceback.</code><code class="descname">format_exception_only</code><span class="sig-paren">(</span><em>etype</em>, <em>value</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.format_exception_only" title="Permalink to this definition"></a></dt>
<dd><p>Format the exception part of a traceback. The arguments are the exception
type and value such as given by <code class="docutils literal notranslate"><span class="pre">sys.last_type</span></code> and <code class="docutils literal notranslate"><span class="pre">sys.last_value</span></code>.
The return value is a list of strings, each ending in a newline. Normally,
the list contains a single string; however, for <a class="reference internal" href="exceptions.html#SyntaxError" title="SyntaxError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SyntaxError</span></code></a>
exceptions, it contains several lines that (when printed) display detailed
information about where the syntax error occurred. The message indicating
which exception occurred is the always last string in the list.</p>
</dd></dl>
<dl class="function">
<dt id="traceback.format_exception">
<code class="descclassname">traceback.</code><code class="descname">format_exception</code><span class="sig-paren">(</span><em>etype</em>, <em>value</em>, <em>tb</em>, <em>limit=None</em>, <em>chain=True</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.format_exception" title="Permalink to this definition"></a></dt>
<dd><p>Format a stack trace and the exception information. The arguments have the
same meaning as the corresponding arguments to <a class="reference internal" href="#traceback.print_exception" title="traceback.print_exception"><code class="xref py py-func docutils literal notranslate"><span class="pre">print_exception()</span></code></a>. The
return value is a list of strings, each ending in a newline and some
containing internal newlines. When these lines are concatenated and printed,
exactly the same text is printed as does <a class="reference internal" href="#traceback.print_exception" title="traceback.print_exception"><code class="xref py py-func docutils literal notranslate"><span class="pre">print_exception()</span></code></a>.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.5: </span>The <em>etype</em> argument is ignored and inferred from the type of <em>value</em>.</p>
</div>
</dd></dl>
<dl class="function">
<dt id="traceback.format_exc">
<code class="descclassname">traceback.</code><code class="descname">format_exc</code><span class="sig-paren">(</span><em>limit=None</em>, <em>chain=True</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.format_exc" title="Permalink to this definition"></a></dt>
<dd><p>This is like <code class="docutils literal notranslate"><span class="pre">print_exc(limit)</span></code> but returns a string instead of printing to
a file.</p>
</dd></dl>
<dl class="function">
<dt id="traceback.format_tb">
<code class="descclassname">traceback.</code><code class="descname">format_tb</code><span class="sig-paren">(</span><em>tb</em>, <em>limit=None</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.format_tb" title="Permalink to this definition"></a></dt>
<dd><p>A shorthand for <code class="docutils literal notranslate"><span class="pre">format_list(extract_tb(tb,</span> <span class="pre">limit))</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="traceback.format_stack">
<code class="descclassname">traceback.</code><code class="descname">format_stack</code><span class="sig-paren">(</span><em>f=None</em>, <em>limit=None</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.format_stack" title="Permalink to this definition"></a></dt>
<dd><p>A shorthand for <code class="docutils literal notranslate"><span class="pre">format_list(extract_stack(f,</span> <span class="pre">limit))</span></code>.</p>
</dd></dl>
<dl class="function">
<dt id="traceback.clear_frames">
<code class="descclassname">traceback.</code><code class="descname">clear_frames</code><span class="sig-paren">(</span><em>tb</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.clear_frames" title="Permalink to this definition"></a></dt>
<dd><p>Clears the local variables of all the stack frames in a traceback <em>tb</em>
by calling the <code class="xref py py-meth docutils literal notranslate"><span class="pre">clear()</span></code> method of each frame object.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.4.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="traceback.walk_stack">
<code class="descclassname">traceback.</code><code class="descname">walk_stack</code><span class="sig-paren">(</span><em>f</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.walk_stack" title="Permalink to this definition"></a></dt>
<dd><p>Walk a stack following <code class="docutils literal notranslate"><span class="pre">f.f_back</span></code> from the given frame, yielding the frame
and line number for each frame. If <em>f</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code>, the current stack is
used. This helper is used with <a class="reference internal" href="#traceback.StackSummary.extract" title="traceback.StackSummary.extract"><code class="xref py py-meth docutils literal notranslate"><span class="pre">StackSummary.extract()</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.5.</span></p>
</div>
</dd></dl>
<dl class="function">
<dt id="traceback.walk_tb">
<code class="descclassname">traceback.</code><code class="descname">walk_tb</code><span class="sig-paren">(</span><em>tb</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.walk_tb" title="Permalink to this definition"></a></dt>
<dd><p>Walk a traceback following <code class="docutils literal notranslate"><span class="pre">tb_next</span></code> yielding the frame and line number
for each frame. This helper is used with <a class="reference internal" href="#traceback.StackSummary.extract" title="traceback.StackSummary.extract"><code class="xref py py-meth docutils literal notranslate"><span class="pre">StackSummary.extract()</span></code></a>.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.5.</span></p>
</div>
</dd></dl>
<p>The module also defines the following classes:</p>
<div class="section" id="tracebackexception-objects">
<h2><a class="reference internal" href="#traceback.TracebackException" title="traceback.TracebackException"><code class="xref py py-class docutils literal notranslate"><span class="pre">TracebackException</span></code></a> Objects<a class="headerlink" href="#tracebackexception-objects" title="Permalink to this headline"></a></h2>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.5.</span></p>
</div>
<p><a class="reference internal" href="#traceback.TracebackException" title="traceback.TracebackException"><code class="xref py py-class docutils literal notranslate"><span class="pre">TracebackException</span></code></a> objects are created from actual exceptions to
capture data for later printing in a lightweight fashion.</p>
<dl class="class">
<dt id="traceback.TracebackException">
<em class="property">class </em><code class="descclassname">traceback.</code><code class="descname">TracebackException</code><span class="sig-paren">(</span><em>exc_type</em>, <em>exc_value</em>, <em>exc_traceback</em>, <em>*</em>, <em>limit=None</em>, <em>lookup_lines=True</em>, <em>capture_locals=False</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.TracebackException" title="Permalink to this definition"></a></dt>
<dd><p>Capture an exception for later rendering. <em>limit</em>, <em>lookup_lines</em> and
<em>capture_locals</em> are as for the <a class="reference internal" href="#traceback.StackSummary" title="traceback.StackSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">StackSummary</span></code></a> class.</p>
<p>Note that when locals are captured, they are also shown in the traceback.</p>
<dl class="attribute">
<dt id="traceback.TracebackException.__cause__">
<code class="descname">__cause__</code><a class="headerlink" href="#traceback.TracebackException.__cause__" title="Permalink to this definition"></a></dt>
<dd><p>A <a class="reference internal" href="#traceback.TracebackException" title="traceback.TracebackException"><code class="xref py py-class docutils literal notranslate"><span class="pre">TracebackException</span></code></a> of the original <code class="docutils literal notranslate"><span class="pre">__cause__</span></code>.</p>
</dd></dl>
<dl class="attribute">
<dt id="traceback.TracebackException.__context__">
<code class="descname">__context__</code><a class="headerlink" href="#traceback.TracebackException.__context__" title="Permalink to this definition"></a></dt>
<dd><p>A <a class="reference internal" href="#traceback.TracebackException" title="traceback.TracebackException"><code class="xref py py-class docutils literal notranslate"><span class="pre">TracebackException</span></code></a> of the original <code class="docutils literal notranslate"><span class="pre">__context__</span></code>.</p>
</dd></dl>
<dl class="attribute">
<dt id="traceback.TracebackException.__suppress_context__">
<code class="descname">__suppress_context__</code><a class="headerlink" href="#traceback.TracebackException.__suppress_context__" title="Permalink to this definition"></a></dt>
<dd><p>The <code class="docutils literal notranslate"><span class="pre">__suppress_context__</span></code> value from the original exception.</p>
</dd></dl>
<dl class="attribute">
<dt id="traceback.TracebackException.stack">
<code class="descname">stack</code><a class="headerlink" href="#traceback.TracebackException.stack" title="Permalink to this definition"></a></dt>
<dd><p>A <a class="reference internal" href="#traceback.StackSummary" title="traceback.StackSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">StackSummary</span></code></a> representing the traceback.</p>
</dd></dl>
<dl class="attribute">
<dt id="traceback.TracebackException.exc_type">
<code class="descname">exc_type</code><a class="headerlink" href="#traceback.TracebackException.exc_type" title="Permalink to this definition"></a></dt>
<dd><p>The class of the original traceback.</p>
</dd></dl>
<dl class="attribute">
<dt id="traceback.TracebackException.filename">
<code class="descname">filename</code><a class="headerlink" href="#traceback.TracebackException.filename" title="Permalink to this definition"></a></dt>
<dd><p>For syntax errors - the file name where the error occurred.</p>
</dd></dl>
<dl class="attribute">
<dt id="traceback.TracebackException.lineno">
<code class="descname">lineno</code><a class="headerlink" href="#traceback.TracebackException.lineno" title="Permalink to this definition"></a></dt>
<dd><p>For syntax errors - the line number where the error occurred.</p>
</dd></dl>
<dl class="attribute">
<dt id="traceback.TracebackException.text">
<code class="descname">text</code><a class="headerlink" href="#traceback.TracebackException.text" title="Permalink to this definition"></a></dt>
<dd><p>For syntax errors - the text where the error occurred.</p>
</dd></dl>
<dl class="attribute">
<dt id="traceback.TracebackException.offset">
<code class="descname">offset</code><a class="headerlink" href="#traceback.TracebackException.offset" title="Permalink to this definition"></a></dt>
<dd><p>For syntax errors - the offset into the text where the error occurred.</p>
</dd></dl>
<dl class="attribute">
<dt id="traceback.TracebackException.msg">
<code class="descname">msg</code><a class="headerlink" href="#traceback.TracebackException.msg" title="Permalink to this definition"></a></dt>
<dd><p>For syntax errors - the compiler error message.</p>
</dd></dl>
<dl class="classmethod">
<dt id="traceback.TracebackException.from_exception">
<em class="property">classmethod </em><code class="descname">from_exception</code><span class="sig-paren">(</span><em>exc</em>, <em>*</em>, <em>limit=None</em>, <em>lookup_lines=True</em>, <em>capture_locals=False</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.TracebackException.from_exception" title="Permalink to this definition"></a></dt>
<dd><p>Capture an exception for later rendering. <em>limit</em>, <em>lookup_lines</em> and
<em>capture_locals</em> are as for the <a class="reference internal" href="#traceback.StackSummary" title="traceback.StackSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">StackSummary</span></code></a> class.</p>
<p>Note that when locals are captured, they are also shown in the traceback.</p>
</dd></dl>
<dl class="method">
<dt id="traceback.TracebackException.format">
<code class="descname">format</code><span class="sig-paren">(</span><em>*</em>, <em>chain=True</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.TracebackException.format" title="Permalink to this definition"></a></dt>
<dd><p>Format the exception.</p>
<p>If <em>chain</em> is not <code class="docutils literal notranslate"><span class="pre">True</span></code>, <code class="docutils literal notranslate"><span class="pre">__cause__</span></code> and <code class="docutils literal notranslate"><span class="pre">__context__</span></code> will not
be formatted.</p>
<p>The return value is a generator of strings, each ending in a newline and
some containing internal newlines. <a class="reference internal" href="#traceback.print_exception" title="traceback.print_exception"><code class="xref py py-func docutils literal notranslate"><span class="pre">print_exception()</span></code></a>
is a wrapper around this method which just prints the lines to a file.</p>
<p>The message indicating which exception occurred is always the last
string in the output.</p>
</dd></dl>
<dl class="method">
<dt id="traceback.TracebackException.format_exception_only">
<code class="descname">format_exception_only</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#traceback.TracebackException.format_exception_only" title="Permalink to this definition"></a></dt>
<dd><p>Format the exception part of the traceback.</p>
<p>The return value is a generator of strings, each ending in a newline.</p>
<p>Normally, the generator emits a single string; however, for
<a class="reference internal" href="exceptions.html#SyntaxError" title="SyntaxError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">SyntaxError</span></code></a> exceptions, it emits several lines that (when
printed) display detailed information about where the syntax
error occurred.</p>
<p>The message indicating which exception occurred is always the last
string in the output.</p>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="stacksummary-objects">
<h2><a class="reference internal" href="#traceback.StackSummary" title="traceback.StackSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">StackSummary</span></code></a> Objects<a class="headerlink" href="#stacksummary-objects" title="Permalink to this headline"></a></h2>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.5.</span></p>
</div>
<p><a class="reference internal" href="#traceback.StackSummary" title="traceback.StackSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">StackSummary</span></code></a> objects represent a call stack ready for formatting.</p>
<dl class="class">
<dt id="traceback.StackSummary">
<em class="property">class </em><code class="descclassname">traceback.</code><code class="descname">StackSummary</code><a class="headerlink" href="#traceback.StackSummary" title="Permalink to this definition"></a></dt>
<dd><dl class="classmethod">
<dt id="traceback.StackSummary.extract">
<em class="property">classmethod </em><code class="descname">extract</code><span class="sig-paren">(</span><em>frame_gen</em>, <em>*</em>, <em>limit=None</em>, <em>lookup_lines=True</em>, <em>capture_locals=False</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.StackSummary.extract" title="Permalink to this definition"></a></dt>
<dd><p>Construct a <a class="reference internal" href="#traceback.StackSummary" title="traceback.StackSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">StackSummary</span></code></a> object from a frame generator (such as
is returned by <a class="reference internal" href="#traceback.walk_stack" title="traceback.walk_stack"><code class="xref py py-func docutils literal notranslate"><span class="pre">walk_stack()</span></code></a> or
<a class="reference internal" href="#traceback.walk_tb" title="traceback.walk_tb"><code class="xref py py-func docutils literal notranslate"><span class="pre">walk_tb()</span></code></a>).</p>
<p>If <em>limit</em> is supplied, only this many frames are taken from <em>frame_gen</em>.
If <em>lookup_lines</em> is <code class="docutils literal notranslate"><span class="pre">False</span></code>, the returned <a class="reference internal" href="#traceback.FrameSummary" title="traceback.FrameSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">FrameSummary</span></code></a>
objects will not have read their lines in yet, making the cost of
creating the <a class="reference internal" href="#traceback.StackSummary" title="traceback.StackSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">StackSummary</span></code></a> cheaper (which may be valuable if it
may not actually get formatted). If <em>capture_locals</em> is <code class="docutils literal notranslate"><span class="pre">True</span></code> the
local variables in each <a class="reference internal" href="#traceback.FrameSummary" title="traceback.FrameSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">FrameSummary</span></code></a> are captured as object
representations.</p>
</dd></dl>
<dl class="classmethod">
<dt id="traceback.StackSummary.from_list">
<em class="property">classmethod </em><code class="descname">from_list</code><span class="sig-paren">(</span><em>a_list</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.StackSummary.from_list" title="Permalink to this definition"></a></dt>
<dd><p>Construct a <a class="reference internal" href="#traceback.StackSummary" title="traceback.StackSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">StackSummary</span></code></a> object from a supplied list of
<a class="reference internal" href="#traceback.FrameSummary" title="traceback.FrameSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">FrameSummary</span></code></a> objects or old-style list of tuples. Each tuple
should be a 4-tuple with filename, lineno, name, line as the elements.</p>
</dd></dl>
<dl class="method">
<dt id="traceback.StackSummary.format">
<code class="descname">format</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#traceback.StackSummary.format" title="Permalink to this definition"></a></dt>
<dd><p>Returns a list of strings ready for printing. Each string in the
resulting list corresponds to a single frame from the stack.
Each string ends in a newline; the strings may contain internal
newlines as well, for those items with source text lines.</p>
<p>For long sequences of the same frame and line, the first few
repetitions are shown, followed by a summary line stating the exact
number of further repetitions.</p>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.6: </span>Long sequences of repeated frames are now abbreviated.</p>
</div>
</dd></dl>
</dd></dl>
</div>
<div class="section" id="framesummary-objects">
<h2><a class="reference internal" href="#traceback.FrameSummary" title="traceback.FrameSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">FrameSummary</span></code></a> Objects<a class="headerlink" href="#framesummary-objects" title="Permalink to this headline"></a></h2>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.5.</span></p>
</div>
<p><a class="reference internal" href="#traceback.FrameSummary" title="traceback.FrameSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">FrameSummary</span></code></a> objects represent a single frame in a traceback.</p>
<dl class="class">
<dt id="traceback.FrameSummary">
<em class="property">class </em><code class="descclassname">traceback.</code><code class="descname">FrameSummary</code><span class="sig-paren">(</span><em>filename</em>, <em>lineno</em>, <em>name</em>, <em>lookup_line=True</em>, <em>locals=None</em>, <em>line=None</em><span class="sig-paren">)</span><a class="headerlink" href="#traceback.FrameSummary" title="Permalink to this definition"></a></dt>
<dd><p>Represent a single frame in the traceback or stack that is being formatted
or printed. It may optionally have a stringified version of the frames
locals included in it. If <em>lookup_line</em> is <code class="docutils literal notranslate"><span class="pre">False</span></code>, the source code is not
looked up until the <a class="reference internal" href="#traceback.FrameSummary" title="traceback.FrameSummary"><code class="xref py py-class docutils literal notranslate"><span class="pre">FrameSummary</span></code></a> has the <code class="xref py py-attr docutils literal notranslate"><span class="pre">line</span></code>
attribute accessed (which also happens when casting it to a tuple).
<code class="xref py py-attr docutils literal notranslate"><span class="pre">line</span></code> may be directly provided, and will prevent line
lookups happening at all. <em>locals</em> is an optional local variable
dictionary, and if supplied the variable representations are stored in the
summary for later display.</p>
</dd></dl>
</div>
<div class="section" id="traceback-examples">
<span id="traceback-example"></span><h2>Traceback Examples<a class="headerlink" href="#traceback-examples" title="Permalink to this headline"></a></h2>
<p>This simple example implements a basic read-eval-print loop, similar to (but
less useful than) the standard Python interactive interpreter loop. For a more
complete implementation of the interpreter loop, refer to the <a class="reference internal" href="code.html#module-code" title="code: Facilities to implement read-eval-print loops."><code class="xref py py-mod docutils literal notranslate"><span class="pre">code</span></code></a>
module.</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">sys</span><span class="o">,</span> <span class="nn">traceback</span>
<span class="k">def</span> <span class="nf">run_user_code</span><span class="p">(</span><span class="n">envdir</span><span class="p">):</span>
<span class="n">source</span> <span class="o">=</span> <span class="nb">input</span><span class="p">(</span><span class="s2">&quot;&gt;&gt;&gt; &quot;</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">exec</span><span class="p">(</span><span class="n">source</span><span class="p">,</span> <span class="n">envdir</span><span class="p">)</span>
<span class="k">except</span> <span class="ne">Exception</span><span class="p">:</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;Exception in user code:&quot;</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;-&quot;</span><span class="o">*</span><span class="mi">60</span><span class="p">)</span>
<span class="n">traceback</span><span class="o">.</span><span class="n">print_exc</span><span class="p">(</span><span class="n">file</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;-&quot;</span><span class="o">*</span><span class="mi">60</span><span class="p">)</span>
<span class="n">envdir</span> <span class="o">=</span> <span class="p">{}</span>
<span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
<span class="n">run_user_code</span><span class="p">(</span><span class="n">envdir</span><span class="p">)</span>
</pre></div>
</div>
<p>The following example demonstrates the different ways to print and format the
exception and traceback:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">sys</span><span class="o">,</span> <span class="nn">traceback</span>
<span class="k">def</span> <span class="nf">lumberjack</span><span class="p">():</span>
<span class="n">bright_side_of_death</span><span class="p">()</span>
<span class="k">def</span> <span class="nf">bright_side_of_death</span><span class="p">():</span>
<span class="k">return</span> <span class="nb">tuple</span><span class="p">()[</span><span class="mi">0</span><span class="p">]</span>
<span class="k">try</span><span class="p">:</span>
<span class="n">lumberjack</span><span class="p">()</span>
<span class="k">except</span> <span class="ne">IndexError</span><span class="p">:</span>
<span class="n">exc_type</span><span class="p">,</span> <span class="n">exc_value</span><span class="p">,</span> <span class="n">exc_traceback</span> <span class="o">=</span> <span class="n">sys</span><span class="o">.</span><span class="n">exc_info</span><span class="p">()</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;*** print_tb:&quot;</span><span class="p">)</span>
<span class="n">traceback</span><span class="o">.</span><span class="n">print_tb</span><span class="p">(</span><span class="n">exc_traceback</span><span class="p">,</span> <span class="n">limit</span><span class="o">=</span><span class="mi">1</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;*** print_exception:&quot;</span><span class="p">)</span>
<span class="c1"># exc_type below is ignored on 3.5 and later</span>
<span class="n">traceback</span><span class="o">.</span><span class="n">print_exception</span><span class="p">(</span><span class="n">exc_type</span><span class="p">,</span> <span class="n">exc_value</span><span class="p">,</span> <span class="n">exc_traceback</span><span class="p">,</span>
<span class="n">limit</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;*** print_exc:&quot;</span><span class="p">)</span>
<span class="n">traceback</span><span class="o">.</span><span class="n">print_exc</span><span class="p">(</span><span class="n">limit</span><span class="o">=</span><span class="mi">2</span><span class="p">,</span> <span class="n">file</span><span class="o">=</span><span class="n">sys</span><span class="o">.</span><span class="n">stdout</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;*** format_exc, first and last line:&quot;</span><span class="p">)</span>
<span class="n">formatted_lines</span> <span class="o">=</span> <span class="n">traceback</span><span class="o">.</span><span class="n">format_exc</span><span class="p">()</span><span class="o">.</span><span class="n">splitlines</span><span class="p">()</span>
<span class="nb">print</span><span class="p">(</span><span class="n">formatted_lines</span><span class="p">[</span><span class="mi">0</span><span class="p">])</span>
<span class="nb">print</span><span class="p">(</span><span class="n">formatted_lines</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">])</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;*** format_exception:&quot;</span><span class="p">)</span>
<span class="c1"># exc_type below is ignored on 3.5 and later</span>
<span class="nb">print</span><span class="p">(</span><span class="nb">repr</span><span class="p">(</span><span class="n">traceback</span><span class="o">.</span><span class="n">format_exception</span><span class="p">(</span><span class="n">exc_type</span><span class="p">,</span> <span class="n">exc_value</span><span class="p">,</span>
<span class="n">exc_traceback</span><span class="p">)))</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;*** extract_tb:&quot;</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="nb">repr</span><span class="p">(</span><span class="n">traceback</span><span class="o">.</span><span class="n">extract_tb</span><span class="p">(</span><span class="n">exc_traceback</span><span class="p">)))</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;*** format_tb:&quot;</span><span class="p">)</span>
<span class="nb">print</span><span class="p">(</span><span class="nb">repr</span><span class="p">(</span><span class="n">traceback</span><span class="o">.</span><span class="n">format_tb</span><span class="p">(</span><span class="n">exc_traceback</span><span class="p">)))</span>
<span class="nb">print</span><span class="p">(</span><span class="s2">&quot;*** tb_lineno:&quot;</span><span class="p">,</span> <span class="n">exc_traceback</span><span class="o">.</span><span class="n">tb_lineno</span><span class="p">)</span>
</pre></div>
</div>
<p>The output for the example would look similar to this:</p>
<div class="highlight-none notranslate"><div class="highlight"><pre><span></span>*** print_tb:
File &quot;&lt;doctest...&gt;&quot;, line 10, in &lt;module&gt;
lumberjack()
*** print_exception:
Traceback (most recent call last):
File &quot;&lt;doctest...&gt;&quot;, line 10, in &lt;module&gt;
lumberjack()
File &quot;&lt;doctest...&gt;&quot;, line 4, in lumberjack
bright_side_of_death()
IndexError: tuple index out of range
*** print_exc:
Traceback (most recent call last):
File &quot;&lt;doctest...&gt;&quot;, line 10, in &lt;module&gt;
lumberjack()
File &quot;&lt;doctest...&gt;&quot;, line 4, in lumberjack
bright_side_of_death()
IndexError: tuple index out of range
*** format_exc, first and last line:
Traceback (most recent call last):
IndexError: tuple index out of range
*** format_exception:
[&#39;Traceback (most recent call last):\n&#39;,
&#39; File &quot;&lt;doctest...&gt;&quot;, line 10, in &lt;module&gt;\n lumberjack()\n&#39;,
&#39; File &quot;&lt;doctest...&gt;&quot;, line 4, in lumberjack\n bright_side_of_death()\n&#39;,
&#39; File &quot;&lt;doctest...&gt;&quot;, line 7, in bright_side_of_death\n return tuple()[0]\n&#39;,
&#39;IndexError: tuple index out of range\n&#39;]
*** extract_tb:
[&lt;FrameSummary file &lt;doctest...&gt;, line 10 in &lt;module&gt;&gt;,
&lt;FrameSummary file &lt;doctest...&gt;, line 4 in lumberjack&gt;,
&lt;FrameSummary file &lt;doctest...&gt;, line 7 in bright_side_of_death&gt;]
*** format_tb:
[&#39; File &quot;&lt;doctest...&gt;&quot;, line 10, in &lt;module&gt;\n lumberjack()\n&#39;,
&#39; File &quot;&lt;doctest...&gt;&quot;, line 4, in lumberjack\n bright_side_of_death()\n&#39;,
&#39; File &quot;&lt;doctest...&gt;&quot;, line 7, in bright_side_of_death\n return tuple()[0]\n&#39;]
*** tb_lineno: 10
</pre></div>
</div>
<p>The following example shows the different ways to print and format the stack:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">traceback</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">another_function</span><span class="p">():</span>
<span class="gp">... </span> <span class="n">lumberstack</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="k">def</span> <span class="nf">lumberstack</span><span class="p">():</span>
<span class="gp">... </span> <span class="n">traceback</span><span class="o">.</span><span class="n">print_stack</span><span class="p">()</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="nb">repr</span><span class="p">(</span><span class="n">traceback</span><span class="o">.</span><span class="n">extract_stack</span><span class="p">()))</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="nb">repr</span><span class="p">(</span><span class="n">traceback</span><span class="o">.</span><span class="n">format_stack</span><span class="p">()))</span>
<span class="gp">...</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">another_function</span><span class="p">()</span>
<span class="go"> File &quot;&lt;doctest&gt;&quot;, line 10, in &lt;module&gt;</span>
<span class="go"> another_function()</span>
<span class="go"> File &quot;&lt;doctest&gt;&quot;, line 3, in another_function</span>
<span class="go"> lumberstack()</span>
<span class="go"> File &quot;&lt;doctest&gt;&quot;, line 6, in lumberstack</span>
<span class="go"> traceback.print_stack()</span>
<span class="go">[(&#39;&lt;doctest&gt;&#39;, 10, &#39;&lt;module&gt;&#39;, &#39;another_function()&#39;),</span>
<span class="go"> (&#39;&lt;doctest&gt;&#39;, 3, &#39;another_function&#39;, &#39;lumberstack()&#39;),</span>
<span class="go"> (&#39;&lt;doctest&gt;&#39;, 7, &#39;lumberstack&#39;, &#39;print(repr(traceback.extract_stack()))&#39;)]</span>
<span class="go">[&#39; File &quot;&lt;doctest&gt;&quot;, line 10, in &lt;module&gt;\n another_function()\n&#39;,</span>
<span class="go"> &#39; File &quot;&lt;doctest&gt;&quot;, line 3, in another_function\n lumberstack()\n&#39;,</span>
<span class="go"> &#39; File &quot;&lt;doctest&gt;&quot;, line 8, in lumberstack\n print(repr(traceback.format_stack()))\n&#39;]</span>
</pre></div>
</div>
<p>This last example demonstrates the final few formatting functions:</p>
<div class="highlight-pycon3 notranslate"><div class="highlight"><pre><span></span><span class="gp">&gt;&gt;&gt; </span><span class="kn">import</span> <span class="nn">traceback</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">traceback</span><span class="o">.</span><span class="n">format_list</span><span class="p">([(</span><span class="s1">&#39;spam.py&#39;</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="s1">&#39;&lt;module&gt;&#39;</span><span class="p">,</span> <span class="s1">&#39;spam.eggs()&#39;</span><span class="p">),</span>
<span class="gp">... </span> <span class="p">(</span><span class="s1">&#39;eggs.py&#39;</span><span class="p">,</span> <span class="mi">42</span><span class="p">,</span> <span class="s1">&#39;eggs&#39;</span><span class="p">,</span> <span class="s1">&#39;return &quot;bacon&quot;&#39;</span><span class="p">)])</span>
<span class="go">[&#39; File &quot;spam.py&quot;, line 3, in &lt;module&gt;\n spam.eggs()\n&#39;,</span>
<span class="go"> &#39; File &quot;eggs.py&quot;, line 42, in eggs\n return &quot;bacon&quot;\n&#39;]</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">an_error</span> <span class="o">=</span> <span class="ne">IndexError</span><span class="p">(</span><span class="s1">&#39;tuple index out of range&#39;</span><span class="p">)</span>
<span class="gp">&gt;&gt;&gt; </span><span class="n">traceback</span><span class="o">.</span><span class="n">format_exception_only</span><span class="p">(</span><span class="nb">type</span><span class="p">(</span><span class="n">an_error</span><span class="p">),</span> <span class="n">an_error</span><span class="p">)</span>
<span class="go">[&#39;IndexError: tuple index out of range\n&#39;]</span>
</pre></div>
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<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">traceback</span></code> — Print or retrieve a stack traceback</a><ul>
<li><a class="reference internal" href="#tracebackexception-objects"><code class="xref py py-class docutils literal notranslate"><span class="pre">TracebackException</span></code> Objects</a></li>
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