Edit File: sched.html
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Data Types</a> »</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body"> <div class="section" id="module-sched"> <span id="sched-event-scheduler"></span><h1>8.8. <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/2.7/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</em>, <em>delayfunc</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). 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> </dd></dl> <p>Example:</p> <div class="highlight-python"><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="k">print</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="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="k">print</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">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="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="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="k">print</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</span> <span class="go">From print_time 930343700.273</span> <span class="go">930343700.276</span> </pre></div> </div> <p>In multi-threaded environments, 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 has limitations with respect to thread-safety, inability to insert a new task before the one currently pending in a running scheduler, and holding up the main thread until the event queue is empty. Instead, the preferred approach is to use the <a class="reference internal" href="threading.html#threading.Timer" title="threading.Timer"><tt class="xref py py-class docutils literal"><span class="pre">threading.Timer</span></tt></a> class instead.</p> <p>Example:</p> <div class="highlight-python"><div class="highlight"><pre><span class="gp">>>> </span><span class="kn">import</span> <span class="nn">time</span> <span class="gp">>>> </span><span class="kn">from</span> <span class="nn">threading</span> <span class="kn">import</span> <span class="n">Timer</span> <span class="gp">>>> </span><span class="k">def</span> <span class="nf">print_time</span><span class="p">():</span> <span class="gp">... </span> <span class="k">print</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="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="k">print</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">Timer</span><span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="n">print_time</span><span class="p">,</span> <span class="p">())</span><span class="o">.</span><span class="n">start</span><span class="p">()</span> <span class="gp">... </span> <span class="n">Timer</span><span class="p">(</span><span class="mi">10</span><span class="p">,</span> <span class="n">print_time</span><span class="p">,</span> <span class="p">())</span><span class="o">.</span><span class="n">start</span><span class="p">()</span> <span class="gp">... </span> <span class="n">time</span><span class="o">.</span><span class="n">sleep</span><span class="p">(</span><span class="mi">11</span><span class="p">)</span> <span class="c"># sleep while time-delay events execute</span> <span class="gp">... </span> <span class="k">print</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</span> <span class="go">From print_time 930343700.273</span> <span class="go">930343701.301</span> </pre></div> </div> <div class="section" id="scheduler-objects"> <span id="id1"></span><h2>8.8.1. 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><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></tt>. <em>argument</em> must be a sequence holding the parameters 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> </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><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> </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#exceptions.ValueError" title="exceptions.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><big>)</big><a class="headerlink" href="#sched.scheduler.run" title="Permalink to this definition">¶</a></dt> <dd><p>Run all scheduled events. This function 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>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> </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.</p> <p class="versionadded"> <span class="versionmodified">New in version 2.6.</span></p> </dd></dl> </div> </div> </div> </div> </div> <div class="sphinxsidebar"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table Of Contents</a></h3> <ul> <li><a class="reference internal" href="#">8.8. <tt class="docutils literal"><span class="pre">sched</span></tt> — Event scheduler</a><ul> <li><a class="reference internal" href="#scheduler-objects">8.8.1. Scheduler Objects</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="sets.html" title="previous chapter">8.7. <tt class="docutils literal"><span class="pre">sets</span></tt> — Unordered collections of unique elements</a></p> <h4>Next topic</h4> <p class="topless"><a href="mutex.html" title="next chapter">8.9. <tt class="docutils literal"><span class="pre">mutex</span></tt> — Mutual exclusion support</a></p> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li><a href="../_sources/library/sched.txt" rel="nofollow">Show Source</a></li> </ul> <div id="searchbox" style="display: none"> <h3>Quick search</h3> <form class="search" action="../search.html" method="get"> <input type="text" name="q" /> <input type="submit" value="Go" /> <input type="hidden" name="check_keywords" value="yes" /> <input type="hidden" name="area" value="default" /> </form> <p class="searchtip" style="font-size: 90%"> Enter search terms or a module, class or function name. </p> </div> <script type="text/javascript">$('#searchbox').show(0);</script> </div> </div> <div class="clearer"></div> </div> <div class="related"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="mutex.html" title="8.9. mutex — Mutual exclusion support" >next</a> |</li> <li class="right" > <a href="sets.html" title="8.7. sets — Unordered collections of unique elements" >previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="http://www.python.org/">Python</a> »</li> <li> <a href="../index.html">Python 2.7.5 documentation</a> » </li> <li><a href="index.html" >The Python Standard Library</a> »</li> <li><a href="datatypes.html" >8. 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