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<div class="section" id="timeout-universal-timeouts">
<h1><tt class="xref docutils literal"><span class="pre">timeout</span></tt> – Universal Timeouts<a class="headerlink" href="#timeout-universal-timeouts" title="Permalink to this headline">¶</a></h1>
<dl class="class">
<dt id="eventlet.timeout.Timeout">
<em class="property">class </em><tt class="descclassname">eventlet.timeout.</tt><tt class="descname">Timeout</tt><a class="headerlink" href="#eventlet.timeout.Timeout" title="Permalink to this definition">¶</a></dt>
<dd><p>Raises <em>exception</em> in the current greenthread after <em>timeout</em> seconds:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">timeout</span> <span class="o">=</span> <span class="n">Timeout</span><span class="p">(</span><span class="n">seconds</span><span class="p">,</span> <span class="n">exception</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="o">...</span> <span class="c"># execution here is limited by timeout</span>
<span class="k">finally</span><span class="p">:</span>
<span class="n">timeout</span><span class="o">.</span><span class="n">cancel</span><span class="p">()</span>
</pre></div>
</div>
<p>When <em>exception</em> is omitted or <tt class="xref docutils literal"><span class="pre">None</span></tt>, the <tt class="xref docutils literal"><span class="pre">Timeout</span></tt> instance
itself is raised:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="n">Timeout</span><span class="p">(</span><span class="mf">0.1</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">eventlet</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mf">0.2</span><span class="p">)</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="nc">Timeout</span>: <span class="n-Identifier">0.1 seconds</span>
</pre></div>
</div>
<p>In Python 2.5 and newer, you can use the <tt class="docutils literal"><span class="pre">with</span></tt> statement for additional
convenience:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="k">with</span> <span class="n">Timeout</span><span class="p">(</span><span class="n">seconds</span><span class="p">,</span> <span class="n">exception</span><span class="p">)</span> <span class="k">as</span> <span class="n">timeout</span><span class="p">:</span>
<span class="k">pass</span> <span class="c"># ... code block ...</span>
</pre></div>
</div>
<p>This is equivalent to the try/finally block in the first example.</p>
<p>There is an additional feature when using the <tt class="docutils literal"><span class="pre">with</span></tt> statement: if
<em>exception</em> is <tt class="xref docutils literal"><span class="pre">False</span></tt>, the timeout is still raised, but the with
statement suppresses it, so the code outside the with-block won’t see it:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">data</span> <span class="o">=</span> <span class="bp">None</span>
<span class="k">with</span> <span class="n">Timeout</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="bp">False</span><span class="p">):</span>
<span class="n">data</span> <span class="o">=</span> <span class="n">mysock</span><span class="o">.</span><span class="n">makefile</span><span class="p">()</span><span class="o">.</span><span class="n">readline</span><span class="p">()</span>
<span class="k">if</span> <span class="n">data</span> <span class="ow">is</span> <span class="bp">None</span><span class="p">:</span>
<span class="o">...</span> <span class="c"># 5 seconds passed without reading a line</span>
<span class="k">else</span><span class="p">:</span>
<span class="o">...</span> <span class="c"># a line was read within 5 seconds</span>
</pre></div>
</div>
<p>As a very special case, if <em>seconds</em> is None, the timer is not scheduled,
and is only useful if you’re planning to raise it directly.</p>
<p>There are two Timeout caveats to be aware of:</p>
<ul class="simple">
<li>If the code block in the try/finally or with-block never cooperatively yields, the timeout cannot be raised. In Eventlet, this should rarely be a problem, but be aware that you cannot time out CPU-only operations with this class.</li>
<li>If the code block catches and doesn’t re-raise <tt class="xref docutils literal"><span class="pre">BaseException</span></tt> (for example, with <tt class="docutils literal"><span class="pre">except:</span></tt>), then it will catch the Timeout exception, and might not abort as intended.</li>
</ul>
<p>When catching timeouts, keep in mind that the one you catch may not be the
one you have set; if you going to silence a timeout, always check that it’s
the same instance that you set:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">timeout</span> <span class="o">=</span> <span class="n">Timeout</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="k">try</span><span class="p">:</span>
<span class="o">...</span>
<span class="k">except</span> <span class="n">Timeout</span><span class="p">,</span> <span class="n">t</span><span class="p">:</span>
<span class="k">if</span> <span class="n">t</span> <span class="ow">is</span> <span class="ow">not</span> <span class="n">timeout</span><span class="p">:</span>
<span class="k">raise</span> <span class="c"># not my timeout</span>
</pre></div>
</div>
<dl class="method">
<dt id="eventlet.timeout.eventlet.timeout.Timeout.Timeout.cancel">
<tt class="descclassname">Timeout.</tt><tt class="descname">cancel</tt><big>(</big><big>)</big><a class="headerlink" href="#eventlet.timeout.eventlet.timeout.Timeout.Timeout.cancel" title="Permalink to this definition">¶</a></dt>
<dd>If the timeout is pending, cancel it. If not using
Timeouts in <tt class="docutils literal"><span class="pre">with</span></tt> statements, always call cancel() in a
<tt class="docutils literal"><span class="pre">finally</span></tt> after the block of code that is getting timed out.
If not canceled, the timeout will be raised later on, in some
unexpected section of the application.</dd></dl>
<dl class="attribute">
<dt id="eventlet.timeout.eventlet.timeout.Timeout.Timeout.pending">
<tt class="descclassname">Timeout.</tt><tt class="descname">pending</tt><a class="headerlink" href="#eventlet.timeout.eventlet.timeout.Timeout.Timeout.pending" title="Permalink to this definition">¶</a></dt>
<dd>True if the timeout is scheduled to be raised.</dd></dl>
</dd></dl>
<dl class="function">
<dt id="eventlet.timeout.with_timeout">
<tt class="descclassname">eventlet.timeout.</tt><tt class="descname">with_timeout</tt><big>(</big><em>seconds</em>, <em>function</em>, <em>*args</em>, <em>**kwds</em><big>)</big><a class="headerlink" href="#eventlet.timeout.with_timeout" title="Permalink to this definition">¶</a></dt>
<dd><p>Wrap a call to some (yielding) function with a timeout; if the called
function fails to return before the timeout, cancel it and return a flag
value.</p>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field"><th class="field-name">Parameters:</th><td class="field-body"><ul class="first simple">
<li><em>seconds</em> (int or float) – seconds before timeout occurs</li>
<li><em>func</em> – the callable to execute with a timeout; it must cooperatively yield, or else the timeout will not be able to trigger</li>
<li><em>*args</em> – positional arguments to pass to <em>func</em></li>
<li><em>**kwds</em> – keyword arguments to pass to <em>func</em></li>
<li><em>timeout_value</em> – value to return if timeout occurs (by default raises
<tt class="xref docutils literal"><span class="pre">Timeout</span></tt>)</li>
</ul>
</td>
</tr>
<tr class="field"><th class="field-name">Return type:</th><td class="field-body"><p class="first">Value returned by <em>func</em> if <em>func</em> returns before <em>seconds</em>, else
<em>timeout_value</em> if provided, else raises <tt class="xref docutils literal"><span class="pre">Timeout</span></tt>.</p>
</td>
</tr>
<tr class="field"><th class="field-name">Raises Timeout:</th><td class="field-body"><p class="first">if <em>func</em> times out and no <tt class="docutils literal"><span class="pre">timeout_value</span></tt> has
been provided.</p>
</td>
</tr>
<tr class="field"><th class="field-name">Exception:</th><td class="field-body"><p class="first last">Any exception raised by <em>func</em></p>
</td>
</tr>
</tbody>
</table>
<p>Example:</p>
<div class="highlight-python"><div class="highlight"><pre><span class="n">data</span> <span class="o">=</span> <span class="n">with_timeout</span><span class="p">(</span><span class="mi">30</span><span class="p">,</span> <span class="n">urllib2</span><span class="o">.</span><span class="n">open</span><span class="p">,</span> <span class="s">'http://www.google.com/'</span><span class="p">,</span> <span class="n">timeout_value</span><span class="o">=</span><span class="s">""</span><span class="p">)</span>
</pre></div>
</div>
<p>Here <em>data</em> is either the result of the <tt class="docutils literal"><span class="pre">get()</span></tt> call, or the empty string
if it took too long to return. Any exception raised by the <tt class="docutils literal"><span class="pre">get()</span></tt> call
is passed through to the caller.</p>
</dd></dl>
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