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<section id="timeout-universal-timeouts">
<h1><code class="xref py py-mod docutils literal notranslate"><span class="pre">timeout</span></code> – Universal Timeouts<a class="headerlink" href="#timeout-universal-timeouts" title="Permalink to this headline">¶</a></h1>
<dl class="py class">
<dt class="sig sig-object py" id="eventlet.timeout.Timeout">
<em class="property"><span class="pre">class</span> </em><span class="sig-prename descclassname"><span class="pre">eventlet.timeout.</span></span><span class="sig-name descname"><span class="pre">Timeout</span></span><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-default notranslate"><div class="highlight"><pre><span></span><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="c1"># 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 is <code class="docutils literal notranslate"><span class="pre">None</span></code>, the <code class="xref py py-class docutils literal notranslate"><span class="pre">Timeout</span></code> instance
itself is raised:</p>
<div class="doctest highlight-default notranslate"><div class="highlight"><pre><span></span><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="gr">Timeout</span>: <span class="n">0.1 seconds</span>
</pre></div>
</div>
<p>You can use the <code class="docutils literal notranslate"><span class="pre">with</span></code> statement for additional convenience:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><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="c1"># ... 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 <code class="docutils literal notranslate"><span class="pre">with</span></code> statement: if
<em>exception</em> is <code class="docutils literal notranslate"><span class="pre">False</span></code>, 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-default notranslate"><div class="highlight"><pre><span></span><span class="n">data</span> <span class="o">=</span> <span class="kc">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="kc">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="kc">None</span><span class="p">:</span>
<span class="o">...</span> <span class="c1"># 5 seconds passed without reading a line</span>
<span class="k">else</span><span class="p">:</span>
<span class="o">...</span> <span class="c1"># 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><p>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.</p></li>
<li><p>If the code block catches and doesn’t re-raise <a class="reference external" href="https://docs.python.org/3/library/exceptions.html#BaseException" title="(in Python v3.9)"><code class="xref py py-class docutils literal notranslate"><span class="pre">BaseException</span></code></a> (for example, with <code class="docutils literal notranslate"><span class="pre">except:</span></code>), then it will catch the Timeout exception, and might not abort as intended.</p></li>
</ul>
<p>When catching timeouts, keep in mind that the one you catch may not be the
one you set; if you plan on silencing a timeout, always check that it’s the
same instance that you set:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><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="k">as</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="c1"># not my timeout</span>
</pre></div>
</div>
<dl class="py method">
<dt class="sig sig-object py" id="eventlet.timeout.eventlet.timeout.Timeout.Timeout.cancel">
<span class="sig-prename descclassname"><span class="pre">Timeout.</span></span><span class="sig-name descname"><span class="pre">cancel</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#eventlet.timeout.eventlet.timeout.Timeout.Timeout.cancel" title="Permalink to this definition">¶</a></dt>
<dd><p>If the timeout is pending, cancel it. If not using
Timeouts in <code class="docutils literal notranslate"><span class="pre">with</span></code> statements, always call cancel() in a
<code class="docutils literal notranslate"><span class="pre">finally</span></code> 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.</p>
</dd></dl>
<dl class="py attribute">
<dt class="sig sig-object py" id="eventlet.timeout.eventlet.timeout.Timeout.Timeout.pending">
<span class="sig-prename descclassname"><span class="pre">Timeout.</span></span><span class="sig-name descname"><span class="pre">pending</span></span><a class="headerlink" href="#eventlet.timeout.eventlet.timeout.Timeout.Timeout.pending" title="Permalink to this definition">¶</a></dt>
<dd><p>True if the timeout is scheduled to be raised.</p>
</dd></dl>
</dd></dl>
<dl class="py function">
<dt class="sig sig-object py" id="eventlet.timeout.with_timeout">
<span class="sig-prename descclassname"><span class="pre">eventlet.timeout.</span></span><span class="sig-name descname"><span class="pre">with_timeout</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">seconds</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">function</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">*</span></span><span class="n"><span class="pre">args</span></span></em>, <em class="sig-param"><span class="o"><span class="pre">**</span></span><span class="n"><span class="pre">kwds</span></span></em><span class="sig-paren">)</span><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>
<dl class="field-list simple">
<dt class="field-odd">Parameters</dt>
<dd class="field-odd"><ul class="simple">
<li><p><strong>seconds</strong> (<a class="reference external" href="https://docs.python.org/3/library/functions.html#int" title="(in Python v3.9)"><em>int</em></a><em> or </em><a class="reference external" href="https://docs.python.org/3/library/functions.html#float" title="(in Python v3.9)"><em>float</em></a>) – seconds before timeout occurs</p></li>
<li><p><strong>func</strong> – the callable to execute with a timeout; it must cooperatively yield, or else the timeout will not be able to trigger</p></li>
<li><p><strong>*args</strong> – positional arguments to pass to <em>func</em></p></li>
<li><p><strong>**kwds</strong> – keyword arguments to pass to <em>func</em></p></li>
<li><p><strong>timeout_value</strong> – value to return if timeout occurs (by default raises
<a class="reference internal" href="#eventlet.timeout.Timeout" title="eventlet.timeout.Timeout"><code class="xref py py-class docutils literal notranslate"><span class="pre">Timeout</span></code></a>)</p></li>
</ul>
</dd>
<dt class="field-even">Return type</dt>
<dd class="field-even"><p>Value returned by <em>func</em> if <em>func</em> returns before <em>seconds</em>, else
<em>timeout_value</em> if provided, else raises <a class="reference internal" href="#eventlet.timeout.Timeout" title="eventlet.timeout.Timeout"><code class="xref py py-class docutils literal notranslate"><span class="pre">Timeout</span></code></a>.</p>
</dd>
<dt class="field-odd">Raises</dt>
<dd class="field-odd"><p><a class="reference internal" href="../basic_usage.html#eventlet.Timeout" title="eventlet.Timeout"><strong>Timeout</strong></a> – if <em>func</em> times out and no <code class="docutils literal notranslate"><span class="pre">timeout_value</span></code> has
been provided.</p>
</dd>
<dt class="field-even">Exception</dt>
<dd class="field-even"><p>Any exception raised by <em>func</em></p>
</dd>
</dl>
<p>Example:</p>
<div class="highlight-default notranslate"><div class="highlight"><pre><span></span><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="s1">'http://www.google.com/'</span><span class="p">,</span> <span class="n">timeout_value</span><span class="o">=</span><span class="s2">""</span><span class="p">)</span>
</pre></div>
</div>
<p>Here <em>data</em> is either the result of the <code class="docutils literal notranslate"><span class="pre">get()</span></code> call, or the empty string
if it took too long to return. Any exception raised by the <code class="docutils literal notranslate"><span class="pre">get()</span></code> call
is passed through to the caller.</p>
</dd></dl>
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