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<div class="section" id="module-sched">
<span id="sched-event-scheduler"></span><h1>17.6. <a class="reference internal" href="#module-sched" title="sched: General purpose event scheduler."><tt class="xref py py-mod docutils literal"><span class="pre">sched</span></tt></a> — Event scheduler<a class="headerlink" href="#module-sched" title="Permalink to this headline">¶</a></h1>
<p id="index-0"><strong>Source code:</strong> <a class="reference external" href="http://hg.python.org/cpython/file/3.3/Lib/sched.py">Lib/sched.py</a></p>
<hr class="docutils" />
<p>The <a class="reference internal" href="#module-sched" title="sched: General purpose event scheduler."><tt class="xref py py-mod docutils literal"><span class="pre">sched</span></tt></a> module defines a class which implements a general purpose event
scheduler:</p>
<dl class="class">
<dt id="sched.scheduler">
<em class="property">class </em><tt class="descclassname">sched.</tt><tt class="descname">scheduler</tt><big>(</big><em>timefunc=time.monotonic</em>, <em>delayfunc=time.sleep</em><big>)</big><a class="headerlink" href="#sched.scheduler" title="Permalink to this definition">¶</a></dt>
<dd><p>The <a class="reference internal" href="#sched.scheduler" title="sched.scheduler"><tt class="xref py py-class docutils literal"><span class="pre">scheduler</span></tt></a> class defines a generic interface to scheduling events.
It needs two functions to actually deal with the “outside world” — <em>timefunc</em>
should be callable without arguments, and return a number (the “time”, in any
units whatsoever). If time.monotonic is not available, the <em>timefunc</em> default
is time.time instead. The <em>delayfunc</em> function should be callable with one
argument, compatible with the output of <em>timefunc</em>, and should delay that many
time units. <em>delayfunc</em> will also be called with the argument <tt class="docutils literal"><span class="pre">0</span></tt> after each
event is run to allow other threads an opportunity to run in multi-threaded
applications.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 3.3:</span> <em>timefunc</em> and <em>delayfunc</em> parameters are optional.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 3.3:</span> <a class="reference internal" href="#sched.scheduler" title="sched.scheduler"><tt class="xref py py-class docutils literal"><span class="pre">scheduler</span></tt></a> class can be safely used in multi-threaded
environments.</p>
</dd></dl>
<p>Example:</p>
<div class="highlight-python3"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">sched</span><span class="o">,</span> <span class="nn">time</span>
<span class="gp">>>> </span><span class="n">s</span> <span class="o">=</span> <span class="n">sched</span><span class="o">.</span><span class="n">scheduler</span><span class="p">(</span><span class="n">time</span><span class="o">.</span><span class="n">time</span><span class="p">,</span> <span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">)</span>
<span class="gp">>>> </span><span class="k">def</span> <span class="nf">print_time</span><span class="p">(</span><span class="n">a</span><span class="o">=</span><span class="s">'default'</span><span class="p">):</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="s">"From print_time"</span><span class="p">,</span> <span class="n">time</span><span class="o">.</span><span class="n">time</span><span class="p">(),</span> <span class="n">a</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="k">def</span> <span class="nf">print_some_times</span><span class="p">():</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">time</span><span class="o">.</span><span class="n">time</span><span class="p">())</span>
<span class="gp">... </span> <span class="n">s</span><span class="o">.</span><span class="n">enter</span><span class="p">(</span><span class="mi">10</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="n">print_time</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">s</span><span class="o">.</span><span class="n">enter</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="n">print_time</span><span class="p">,</span> <span class="n">argument</span><span class="o">=</span><span class="p">(</span><span class="s">'positional'</span><span class="p">,))</span>
<span class="gp">... </span> <span class="n">s</span><span class="o">.</span><span class="n">enter</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="n">print_time</span><span class="p">,</span> <span class="n">kwargs</span><span class="o">=</span><span class="p">{</span><span class="s">'a'</span><span class="p">:</span> <span class="s">'keyword'</span><span class="p">})</span>
<span class="gp">... </span> <span class="n">s</span><span class="o">.</span><span class="n">run</span><span class="p">()</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">time</span><span class="o">.</span><span class="n">time</span><span class="p">())</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">print_some_times</span><span class="p">()</span>
<span class="go">930343690.257</span>
<span class="go">From print_time 930343695.274 positional</span>
<span class="go">From print_time 930343695.275 keyword</span>
<span class="go">From print_time 930343700.273 default</span>
<span class="go">930343700.276</span>
</pre></div>
</div>
<div class="section" id="scheduler-objects">
<span id="id1"></span><h2>17.6.1. Scheduler Objects<a class="headerlink" href="#scheduler-objects" title="Permalink to this headline">¶</a></h2>
<p><a class="reference internal" href="#sched.scheduler" title="sched.scheduler"><tt class="xref py py-class docutils literal"><span class="pre">scheduler</span></tt></a> instances have the following methods and attributes:</p>
<dl class="method">
<dt id="sched.scheduler.enterabs">
<tt class="descclassname">scheduler.</tt><tt class="descname">enterabs</tt><big>(</big><em>time</em>, <em>priority</em>, <em>action</em>, <em>argument=()</em>, <em>kwargs={}</em><big>)</big><a class="headerlink" href="#sched.scheduler.enterabs" title="Permalink to this definition">¶</a></dt>
<dd><p>Schedule a new event. The <em>time</em> argument should be a numeric type compatible
with the return value of the <em>timefunc</em> function passed to the constructor.
Events scheduled for the same <em>time</em> will be executed in the order of their
<em>priority</em>.</p>
<p>Executing the event means executing <tt class="docutils literal"><span class="pre">action(*argument,</span> <span class="pre">**kwargs)</span></tt>.
<em>argument</em> is a sequence holding the positional arguments for <em>action</em>.
<em>kwargs</em> is a dictionary holding the keyword arguments for <em>action</em>.</p>
<p>Return value is an event which may be used for later cancellation of the event
(see <a class="reference internal" href="#sched.scheduler.cancel" title="sched.scheduler.cancel"><tt class="xref py py-meth docutils literal"><span class="pre">cancel()</span></tt></a>).</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 3.3:</span> <em>argument</em> parameter is optional.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.3:</span> <em>kwargs</em> parameter was added.</p>
</dd></dl>
<dl class="method">
<dt id="sched.scheduler.enter">
<tt class="descclassname">scheduler.</tt><tt class="descname">enter</tt><big>(</big><em>delay</em>, <em>priority</em>, <em>action</em>, <em>argument=()</em>, <em>kwargs={}</em><big>)</big><a class="headerlink" href="#sched.scheduler.enter" title="Permalink to this definition">¶</a></dt>
<dd><p>Schedule an event for <em>delay</em> more time units. Other than the relative time, the
other arguments, the effect and the return value are the same as those for
<a class="reference internal" href="#sched.scheduler.enterabs" title="sched.scheduler.enterabs"><tt class="xref py py-meth docutils literal"><span class="pre">enterabs()</span></tt></a>.</p>
<p class="versionchanged">
<span class="versionmodified">Changed in version 3.3:</span> <em>argument</em> parameter is optional.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.3:</span> <em>kwargs</em> parameter was added.</p>
</dd></dl>
<dl class="method">
<dt id="sched.scheduler.cancel">
<tt class="descclassname">scheduler.</tt><tt class="descname">cancel</tt><big>(</big><em>event</em><big>)</big><a class="headerlink" href="#sched.scheduler.cancel" title="Permalink to this definition">¶</a></dt>
<dd><p>Remove the event from the queue. If <em>event</em> is not an event currently in the
queue, this method will raise a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><tt class="xref py py-exc docutils literal"><span class="pre">ValueError</span></tt></a>.</p>
</dd></dl>
<dl class="method">
<dt id="sched.scheduler.empty">
<tt class="descclassname">scheduler.</tt><tt class="descname">empty</tt><big>(</big><big>)</big><a class="headerlink" href="#sched.scheduler.empty" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if the event queue is empty.</p>
</dd></dl>
<dl class="method">
<dt id="sched.scheduler.run">
<tt class="descclassname">scheduler.</tt><tt class="descname">run</tt><big>(</big><em>blocking=True</em><big>)</big><a class="headerlink" href="#sched.scheduler.run" title="Permalink to this definition">¶</a></dt>
<dd><p>Run all scheduled events. This method will wait (using the <tt class="xref py py-func docutils literal"><span class="pre">delayfunc()</span></tt>
function passed to the constructor) for the next event, then execute it and so
on until there are no more scheduled events.</p>
<p>If <em>blocking</em> is False executes the scheduled events due to expire soonest
(if any) and then return the deadline of the next scheduled call in the
scheduler (if any).</p>
<p>Either <em>action</em> or <em>delayfunc</em> can raise an exception. In either case, the
scheduler will maintain a consistent state and propagate the exception. If an
exception is raised by <em>action</em>, the event will not be attempted in future calls
to <a class="reference internal" href="#sched.scheduler.run" title="sched.scheduler.run"><tt class="xref py py-meth docutils literal"><span class="pre">run()</span></tt></a>.</p>
<p>If a sequence of events takes longer to run than the time available before the
next event, the scheduler will simply fall behind. No events will be dropped;
the calling code is responsible for canceling events which are no longer
pertinent.</p>
<p class="versionadded">
<span class="versionmodified">New in version 3.3:</span> <em>blocking</em> parameter was added.</p>
</dd></dl>
<dl class="attribute">
<dt id="sched.scheduler.queue">
<tt class="descclassname">scheduler.</tt><tt class="descname">queue</tt><a class="headerlink" href="#sched.scheduler.queue" title="Permalink to this definition">¶</a></dt>
<dd><p>Read-only attribute returning a list of upcoming events in the order they
will be run. Each event is shown as a <a class="reference internal" href="../glossary.html#term-named-tuple"><em class="xref std std-term">named tuple</em></a> with the
following fields: time, priority, action, argument, kwargs.</p>
</dd></dl>
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