<!DOCTYPE html> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <meta charset="utf-8" /> <title>selectors — High-level I/O multiplexing — Python 3.7.10 documentation</title> <link rel="stylesheet" href="../_static/pydoctheme.css" type="text/css" /> <link rel="stylesheet" href="../_static/pygments.css" type="text/css" /> <script type="text/javascript" id="documentation_options" data-url_root="../" src="../_static/documentation_options.js"></script> <script type="text/javascript" src="../_static/jquery.js"></script> <script type="text/javascript" src="../_static/underscore.js"></script> <script type="text/javascript" src="../_static/doctools.js"></script> <script type="text/javascript" src="../_static/language_data.js"></script> <script type="text/javascript" src="../_static/sidebar.js"></script> <link rel="search" type="application/opensearchdescription+xml" title="Search within Python 3.7.10 documentation" href="../_static/opensearch.xml"/> <link rel="author" title="About these documents" href="../about.html" /> <link rel="index" title="Index" href="../genindex.html" /> <link rel="search" title="Search" href="../search.html" /> <link rel="copyright" title="Copyright" href="../copyright.html" /> <link rel="next" title="asyncore — Asynchronous socket handler" href="asyncore.html" /> <link rel="prev" title="select — Waiting for I/O completion" href="select.html" /> <link rel="shortcut icon" type="image/png" href="../_static/py.png" /> <link rel="canonical" href="https://docs.python.org/3/library/selectors.html" /> <script type="text/javascript" src="../_static/copybutton.js"></script> <style> @media only screen { table.full-width-table { width: 100%; } } </style> </head><body> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" accesskey="I">index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="asyncore.html" title="asyncore — Asynchronous socket handler" accesskey="N">next</a> |</li> <li class="right" > <a href="select.html" title="select — Waiting for I/O completion" accesskey="P">previous</a> |</li> <li><img src="../_static/py.png" alt="" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li> <a href="../index.html">3.7.10 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="ipc.html" accesskey="U">Networking and Interprocess Communication</a> »</li> <li class="right"> <div class="inline-search" style="display: none" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" 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> </div> <script type="text/javascript">$('.inline-search').show(0);</script> | </li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <div class="section" id="module-selectors"> <span id="selectors-high-level-i-o-multiplexing"></span><h1><a class="reference internal" href="#module-selectors" title="selectors: High-level I/O multiplexing."><code class="xref py py-mod docutils literal notranslate"><span class="pre">selectors</span></code></a> — High-level I/O multiplexing<a class="headerlink" href="#module-selectors" title="Permalink to this headline">¶</a></h1> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.4.</span></p> </div> <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/selectors.py">Lib/selectors.py</a></p> <hr class="docutils" /> <div class="section" id="introduction"> <h2>Introduction<a class="headerlink" href="#introduction" title="Permalink to this headline">¶</a></h2> <p>This module allows high-level and efficient I/O multiplexing, built upon the <a class="reference internal" href="select.html#module-select" title="select: Wait for I/O completion on multiple streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">select</span></code></a> module primitives. Users are encouraged to use this module instead, unless they want precise control over the OS-level primitives used.</p> <p>It defines a <a class="reference internal" href="#selectors.BaseSelector" title="selectors.BaseSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">BaseSelector</span></code></a> abstract base class, along with several concrete implementations (<a class="reference internal" href="#selectors.KqueueSelector" title="selectors.KqueueSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">KqueueSelector</span></code></a>, <a class="reference internal" href="#selectors.EpollSelector" title="selectors.EpollSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">EpollSelector</span></code></a>…), that can be used to wait for I/O readiness notification on multiple file objects. In the following, “file object” refers to any object with a <code class="xref py py-meth docutils literal notranslate"><span class="pre">fileno()</span></code> method, or a raw file descriptor. See <a class="reference internal" href="../glossary.html#term-file-object"><span class="xref std std-term">file object</span></a>.</p> <p><a class="reference internal" href="#selectors.DefaultSelector" title="selectors.DefaultSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">DefaultSelector</span></code></a> is an alias to the most efficient implementation available on the current platform: this should be the default choice for most users.</p> <div class="admonition note"> <p class="admonition-title">Note</p> <p>The type of file objects supported depends on the platform: on Windows, sockets are supported, but not pipes, whereas on Unix, both are supported (some other types may be supported as well, such as fifos or special file devices).</p> </div> <div class="admonition seealso"> <p class="admonition-title">See also</p> <dl class="simple"> <dt><a class="reference internal" href="select.html#module-select" title="select: Wait for I/O completion on multiple streams."><code class="xref py py-mod docutils literal notranslate"><span class="pre">select</span></code></a></dt><dd><p>Low-level I/O multiplexing module.</p> </dd> </dl> </div> </div> <div class="section" id="classes"> <h2>Classes<a class="headerlink" href="#classes" title="Permalink to this headline">¶</a></h2> <p>Classes hierarchy:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">BaseSelector</span> <span class="o">+--</span> <span class="n">SelectSelector</span> <span class="o">+--</span> <span class="n">PollSelector</span> <span class="o">+--</span> <span class="n">EpollSelector</span> <span class="o">+--</span> <span class="n">DevpollSelector</span> <span class="o">+--</span> <span class="n">KqueueSelector</span> </pre></div> </div> <p>In the following, <em>events</em> is a bitwise mask indicating which I/O events should be waited for on a given file object. It can be a combination of the modules constants below:</p> <blockquote> <div><table class="docutils align-default"> <colgroup> <col style="width: 33%" /> <col style="width: 67%" /> </colgroup> <thead> <tr class="row-odd"><th class="head"><p>Constant</p></th> <th class="head"><p>Meaning</p></th> </tr> </thead> <tbody> <tr class="row-even"><td><p><code class="xref py py-const docutils literal notranslate"><span class="pre">EVENT_READ</span></code></p></td> <td><p>Available for read</p></td> </tr> <tr class="row-odd"><td><p><code class="xref py py-const docutils literal notranslate"><span class="pre">EVENT_WRITE</span></code></p></td> <td><p>Available for write</p></td> </tr> </tbody> </table> </div></blockquote> <dl class="class"> <dt id="selectors.SelectorKey"> <em class="property">class </em><code class="sig-prename descclassname">selectors.</code><code class="sig-name descname">SelectorKey</code><a class="headerlink" href="#selectors.SelectorKey" title="Permalink to this definition">¶</a></dt> <dd><p>A <a class="reference internal" href="#selectors.SelectorKey" title="selectors.SelectorKey"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorKey</span></code></a> is a <a class="reference internal" href="collections.html#collections.namedtuple" title="collections.namedtuple"><code class="xref py py-class docutils literal notranslate"><span class="pre">namedtuple</span></code></a> used to associate a file object to its underlying file descriptor, selected event mask and attached data. It is returned by several <a class="reference internal" href="#selectors.BaseSelector" title="selectors.BaseSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">BaseSelector</span></code></a> methods.</p> <dl class="attribute"> <dt id="selectors.SelectorKey.fileobj"> <code class="sig-name descname">fileobj</code><a class="headerlink" href="#selectors.SelectorKey.fileobj" title="Permalink to this definition">¶</a></dt> <dd><p>File object registered.</p> </dd></dl> <dl class="attribute"> <dt id="selectors.SelectorKey.fd"> <code class="sig-name descname">fd</code><a class="headerlink" href="#selectors.SelectorKey.fd" title="Permalink to this definition">¶</a></dt> <dd><p>Underlying file descriptor.</p> </dd></dl> <dl class="attribute"> <dt id="selectors.SelectorKey.events"> <code class="sig-name descname">events</code><a class="headerlink" href="#selectors.SelectorKey.events" title="Permalink to this definition">¶</a></dt> <dd><p>Events that must be waited for on this file object.</p> </dd></dl> <dl class="attribute"> <dt id="selectors.SelectorKey.data"> <code class="sig-name descname">data</code><a class="headerlink" href="#selectors.SelectorKey.data" title="Permalink to this definition">¶</a></dt> <dd><p>Optional opaque data associated to this file object: for example, this could be used to store a per-client session ID.</p> </dd></dl> </dd></dl> <dl class="class"> <dt id="selectors.BaseSelector"> <em class="property">class </em><code class="sig-prename descclassname">selectors.</code><code class="sig-name descname">BaseSelector</code><a class="headerlink" href="#selectors.BaseSelector" title="Permalink to this definition">¶</a></dt> <dd><p>A <a class="reference internal" href="#selectors.BaseSelector" title="selectors.BaseSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">BaseSelector</span></code></a> is used to wait for I/O event readiness on multiple file objects. It supports file stream registration, unregistration, and a method to wait for I/O events on those streams, with an optional timeout. It’s an abstract base class, so cannot be instantiated. Use <a class="reference internal" href="#selectors.DefaultSelector" title="selectors.DefaultSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">DefaultSelector</span></code></a> instead, or one of <a class="reference internal" href="#selectors.SelectSelector" title="selectors.SelectSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectSelector</span></code></a>, <a class="reference internal" href="#selectors.KqueueSelector" title="selectors.KqueueSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">KqueueSelector</span></code></a> etc. if you want to specifically use an implementation, and your platform supports it. <a class="reference internal" href="#selectors.BaseSelector" title="selectors.BaseSelector"><code class="xref py py-class docutils literal notranslate"><span class="pre">BaseSelector</span></code></a> and its concrete implementations support the <a class="reference internal" href="../glossary.html#term-context-manager"><span class="xref std std-term">context manager</span></a> protocol.</p> <dl class="method"> <dt id="selectors.BaseSelector.register"> <em class="property">abstractmethod </em><code class="sig-name descname">register</code><span class="sig-paren">(</span><em class="sig-param">fileobj</em>, <em class="sig-param">events</em>, <em class="sig-param">data=None</em><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.register" title="Permalink to this definition">¶</a></dt> <dd><p>Register a file object for selection, monitoring it for I/O events.</p> <p><em>fileobj</em> is the file object to monitor. It may either be an integer file descriptor or an object with a <code class="docutils literal notranslate"><span class="pre">fileno()</span></code> method. <em>events</em> is a bitwise mask of events to monitor. <em>data</em> is an opaque object.</p> <p>This returns a new <a class="reference internal" href="#selectors.SelectorKey" title="selectors.SelectorKey"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorKey</span></code></a> instance, or raises a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> in case of invalid event mask or file descriptor, or <a class="reference internal" href="exceptions.html#KeyError" title="KeyError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyError</span></code></a> if the file object is already registered.</p> </dd></dl> <dl class="method"> <dt id="selectors.BaseSelector.unregister"> <em class="property">abstractmethod </em><code class="sig-name descname">unregister</code><span class="sig-paren">(</span><em class="sig-param">fileobj</em><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.unregister" title="Permalink to this definition">¶</a></dt> <dd><p>Unregister a file object from selection, removing it from monitoring. A file object shall be unregistered prior to being closed.</p> <p><em>fileobj</em> must be a file object previously registered.</p> <p>This returns the associated <a class="reference internal" href="#selectors.SelectorKey" title="selectors.SelectorKey"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorKey</span></code></a> instance, or raises a <a class="reference internal" href="exceptions.html#KeyError" title="KeyError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyError</span></code></a> if <em>fileobj</em> is not registered. It will raise <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> if <em>fileobj</em> is invalid (e.g. it has no <code class="docutils literal notranslate"><span class="pre">fileno()</span></code> method or its <code class="docutils literal notranslate"><span class="pre">fileno()</span></code> method has an invalid return value).</p> </dd></dl> <dl class="method"> <dt id="selectors.BaseSelector.modify"> <code class="sig-name descname">modify</code><span class="sig-paren">(</span><em class="sig-param">fileobj</em>, <em class="sig-param">events</em>, <em class="sig-param">data=None</em><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.modify" title="Permalink to this definition">¶</a></dt> <dd><p>Change a registered file object’s monitored events or attached data.</p> <p>This is equivalent to <code class="xref py py-meth docutils literal notranslate"><span class="pre">BaseSelector.unregister(fileobj)()</span></code> followed by <code class="xref py py-meth docutils literal notranslate"><span class="pre">BaseSelector.register(fileobj,</span> <span class="pre">events,</span> <span class="pre">data)()</span></code>, except that it can be implemented more efficiently.</p> <p>This returns a new <a class="reference internal" href="#selectors.SelectorKey" title="selectors.SelectorKey"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorKey</span></code></a> instance, or raises a <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> in case of invalid event mask or file descriptor, or <a class="reference internal" href="exceptions.html#KeyError" title="KeyError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyError</span></code></a> if the file object is not registered.</p> </dd></dl> <dl class="method"> <dt id="selectors.BaseSelector.select"> <em class="property">abstractmethod </em><code class="sig-name descname">select</code><span class="sig-paren">(</span><em class="sig-param">timeout=None</em><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.select" title="Permalink to this definition">¶</a></dt> <dd><p>Wait until some registered file objects become ready, or the timeout expires.</p> <p>If <code class="docutils literal notranslate"><span class="pre">timeout</span> <span class="pre">></span> <span class="pre">0</span></code>, this specifies the maximum wait time, in seconds. If <code class="docutils literal notranslate"><span class="pre">timeout</span> <span class="pre"><=</span> <span class="pre">0</span></code>, the call won’t block, and will report the currently ready file objects. If <em>timeout</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code>, the call will block until a monitored file object becomes ready.</p> <p>This returns a list of <code class="docutils literal notranslate"><span class="pre">(key,</span> <span class="pre">events)</span></code> tuples, one for each ready file object.</p> <p><em>key</em> is the <a class="reference internal" href="#selectors.SelectorKey" title="selectors.SelectorKey"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorKey</span></code></a> instance corresponding to a ready file object. <em>events</em> is a bitmask of events ready on this file object.</p> <div class="admonition note"> <p class="admonition-title">Note</p> <p>This method can return before any file object becomes ready or the timeout has elapsed if the current process receives a signal: in this case, an empty list will be returned.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.5: </span>The selector is now retried with a recomputed timeout when interrupted by a signal if the signal handler did not raise an exception (see <span class="target" id="index-0"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-0475"><strong>PEP 475</strong></a> for the rationale), instead of returning an empty list of events before the timeout.</p> </div> </dd></dl> <dl class="method"> <dt id="selectors.BaseSelector.close"> <code class="sig-name descname">close</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.close" title="Permalink to this definition">¶</a></dt> <dd><p>Close the selector.</p> <p>This must be called to make sure that any underlying resource is freed. The selector shall not be used once it has been closed.</p> </dd></dl> <dl class="method"> <dt id="selectors.BaseSelector.get_key"> <code class="sig-name descname">get_key</code><span class="sig-paren">(</span><em class="sig-param">fileobj</em><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.get_key" title="Permalink to this definition">¶</a></dt> <dd><p>Return the key associated with a registered file object.</p> <p>This returns the <a class="reference internal" href="#selectors.SelectorKey" title="selectors.SelectorKey"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorKey</span></code></a> instance associated to this file object, or raises <a class="reference internal" href="exceptions.html#KeyError" title="KeyError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyError</span></code></a> if the file object is not registered.</p> </dd></dl> <dl class="method"> <dt id="selectors.BaseSelector.get_map"> <em class="property">abstractmethod </em><code class="sig-name descname">get_map</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.get_map" title="Permalink to this definition">¶</a></dt> <dd><p>Return a mapping of file objects to selector keys.</p> <p>This returns a <a class="reference internal" href="collections.abc.html#collections.abc.Mapping" title="collections.abc.Mapping"><code class="xref py py-class docutils literal notranslate"><span class="pre">Mapping</span></code></a> instance mapping registered file objects to their associated <a class="reference internal" href="#selectors.SelectorKey" title="selectors.SelectorKey"><code class="xref py py-class docutils literal notranslate"><span class="pre">SelectorKey</span></code></a> instance.</p> </dd></dl> </dd></dl> <dl class="class"> <dt id="selectors.DefaultSelector"> <em class="property">class </em><code class="sig-prename descclassname">selectors.</code><code class="sig-name descname">DefaultSelector</code><a class="headerlink" href="#selectors.DefaultSelector" title="Permalink to this definition">¶</a></dt> <dd><p>The default selector class, using the most efficient implementation available on the current platform. This should be the default choice for most users.</p> </dd></dl> <dl class="class"> <dt id="selectors.SelectSelector"> <em class="property">class </em><code class="sig-prename descclassname">selectors.</code><code class="sig-name descname">SelectSelector</code><a class="headerlink" href="#selectors.SelectSelector" title="Permalink to this definition">¶</a></dt> <dd><p><a class="reference internal" href="select.html#select.select" title="select.select"><code class="xref py py-func docutils literal notranslate"><span class="pre">select.select()</span></code></a>-based selector.</p> </dd></dl> <dl class="class"> <dt id="selectors.PollSelector"> <em class="property">class </em><code class="sig-prename descclassname">selectors.</code><code class="sig-name descname">PollSelector</code><a class="headerlink" href="#selectors.PollSelector" title="Permalink to this definition">¶</a></dt> <dd><p><a class="reference internal" href="select.html#select.poll" title="select.poll"><code class="xref py py-func docutils literal notranslate"><span class="pre">select.poll()</span></code></a>-based selector.</p> </dd></dl> <dl class="class"> <dt id="selectors.EpollSelector"> <em class="property">class </em><code class="sig-prename descclassname">selectors.</code><code class="sig-name descname">EpollSelector</code><a class="headerlink" href="#selectors.EpollSelector" title="Permalink to this definition">¶</a></dt> <dd><p><a class="reference internal" href="select.html#select.epoll" title="select.epoll"><code class="xref py py-func docutils literal notranslate"><span class="pre">select.epoll()</span></code></a>-based selector.</p> <dl class="method"> <dt id="selectors.EpollSelector.fileno"> <code class="sig-name descname">fileno</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#selectors.EpollSelector.fileno" title="Permalink to this definition">¶</a></dt> <dd><p>This returns the file descriptor used by the underlying <a class="reference internal" href="select.html#select.epoll" title="select.epoll"><code class="xref py py-func docutils literal notranslate"><span class="pre">select.epoll()</span></code></a> object.</p> </dd></dl> </dd></dl> <dl class="class"> <dt id="selectors.DevpollSelector"> <em class="property">class </em><code class="sig-prename descclassname">selectors.</code><code class="sig-name descname">DevpollSelector</code><a class="headerlink" href="#selectors.DevpollSelector" title="Permalink to this definition">¶</a></dt> <dd><p><a class="reference internal" href="select.html#select.devpoll" title="select.devpoll"><code class="xref py py-func docutils literal notranslate"><span class="pre">select.devpoll()</span></code></a>-based selector.</p> <dl class="method"> <dt id="selectors.DevpollSelector.fileno"> <code class="sig-name descname">fileno</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#selectors.DevpollSelector.fileno" title="Permalink to this definition">¶</a></dt> <dd><p>This returns the file descriptor used by the underlying <a class="reference internal" href="select.html#select.devpoll" title="select.devpoll"><code class="xref py py-func docutils literal notranslate"><span class="pre">select.devpoll()</span></code></a> object.</p> </dd></dl> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.5.</span></p> </div> </dd></dl> <dl class="class"> <dt id="selectors.KqueueSelector"> <em class="property">class </em><code class="sig-prename descclassname">selectors.</code><code class="sig-name descname">KqueueSelector</code><a class="headerlink" href="#selectors.KqueueSelector" title="Permalink to this definition">¶</a></dt> <dd><p><a class="reference internal" href="select.html#select.kqueue" title="select.kqueue"><code class="xref py py-func docutils literal notranslate"><span class="pre">select.kqueue()</span></code></a>-based selector.</p> <dl class="method"> <dt id="selectors.KqueueSelector.fileno"> <code class="sig-name descname">fileno</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#selectors.KqueueSelector.fileno" title="Permalink to this definition">¶</a></dt> <dd><p>This returns the file descriptor used by the underlying <a class="reference internal" href="select.html#select.kqueue" title="select.kqueue"><code class="xref py py-func docutils literal notranslate"><span class="pre">select.kqueue()</span></code></a> object.</p> </dd></dl> </dd></dl> </div> <div class="section" id="examples"> <h2>Examples<a class="headerlink" href="#examples" title="Permalink to this headline">¶</a></h2> <p>Here is a simple echo server implementation:</p> <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">selectors</span> <span class="kn">import</span> <span class="nn">socket</span> <span class="n">sel</span> <span class="o">=</span> <span class="n">selectors</span><span class="o">.</span><span class="n">DefaultSelector</span><span class="p">()</span> <span class="k">def</span> <span class="nf">accept</span><span class="p">(</span><span class="n">sock</span><span class="p">,</span> <span class="n">mask</span><span class="p">):</span> <span class="n">conn</span><span class="p">,</span> <span class="n">addr</span> <span class="o">=</span> <span class="n">sock</span><span class="o">.</span><span class="n">accept</span><span class="p">()</span> <span class="c1"># Should be ready</span> <span class="nb">print</span><span class="p">(</span><span class="s1">'accepted'</span><span class="p">,</span> <span class="n">conn</span><span class="p">,</span> <span class="s1">'from'</span><span class="p">,</span> <span class="n">addr</span><span class="p">)</span> <span class="n">conn</span><span class="o">.</span><span class="n">setblocking</span><span class="p">(</span><span class="kc">False</span><span class="p">)</span> <span class="n">sel</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="n">conn</span><span class="p">,</span> <span class="n">selectors</span><span class="o">.</span><span class="n">EVENT_READ</span><span class="p">,</span> <span class="n">read</span><span class="p">)</span> <span class="k">def</span> <span class="nf">read</span><span class="p">(</span><span class="n">conn</span><span class="p">,</span> <span class="n">mask</span><span class="p">):</span> <span class="n">data</span> <span class="o">=</span> <span class="n">conn</span><span class="o">.</span><span class="n">recv</span><span class="p">(</span><span class="mi">1000</span><span class="p">)</span> <span class="c1"># Should be ready</span> <span class="k">if</span> <span class="n">data</span><span class="p">:</span> <span class="nb">print</span><span class="p">(</span><span class="s1">'echoing'</span><span class="p">,</span> <span class="nb">repr</span><span class="p">(</span><span class="n">data</span><span class="p">),</span> <span class="s1">'to'</span><span class="p">,</span> <span class="n">conn</span><span class="p">)</span> <span class="n">conn</span><span class="o">.</span><span class="n">send</span><span class="p">(</span><span class="n">data</span><span class="p">)</span> <span class="c1"># Hope it won't block</span> <span class="k">else</span><span class="p">:</span> <span class="nb">print</span><span class="p">(</span><span class="s1">'closing'</span><span class="p">,</span> <span class="n">conn</span><span class="p">)</span> <span class="n">sel</span><span class="o">.</span><span class="n">unregister</span><span class="p">(</span><span class="n">conn</span><span class="p">)</span> <span class="n">conn</span><span class="o">.</span><span class="n">close</span><span class="p">()</span> <span class="n">sock</span> <span class="o">=</span> <span class="n">socket</span><span class="o">.</span><span class="n">socket</span><span class="p">()</span> <span class="n">sock</span><span class="o">.</span><span class="n">bind</span><span class="p">((</span><span class="s1">'localhost'</span><span class="p">,</span> <span class="mi">1234</span><span class="p">))</span> <span class="n">sock</span><span class="o">.</span><span class="n">listen</span><span class="p">(</span><span class="mi">100</span><span class="p">)</span> <span class="n">sock</span><span class="o">.</span><span class="n">setblocking</span><span class="p">(</span><span class="kc">False</span><span class="p">)</span> <span class="n">sel</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="n">sock</span><span class="p">,</span> <span class="n">selectors</span><span class="o">.</span><span class="n">EVENT_READ</span><span class="p">,</span> <span class="n">accept</span><span class="p">)</span> <span class="k">while</span> <span class="kc">True</span><span class="p">:</span> <span class="n">events</span> <span class="o">=</span> <span class="n">sel</span><span class="o">.</span><span class="n">select</span><span class="p">()</span> <span class="k">for</span> <span class="n">key</span><span class="p">,</span> <span class="n">mask</span> <span class="ow">in</span> <span class="n">events</span><span class="p">:</span> <span class="n">callback</span> <span class="o">=</span> <span class="n">key</span><span class="o">.</span><span class="n">data</span> <span class="n">callback</span><span class="p">(</span><span class="n">key</span><span class="o">.</span><span class="n">fileobj</span><span class="p">,</span> <span class="n">mask</span><span class="p">)</span> </pre></div> </div> </div> </div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <h3><a href="../contents.html">Table of Contents</a></h3> <ul> <li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">selectors</span></code> — High-level I/O multiplexing</a><ul> <li><a class="reference internal" href="#introduction">Introduction</a></li> <li><a class="reference internal" href="#classes">Classes</a></li> <li><a class="reference internal" href="#examples">Examples</a></li> </ul> </li> </ul> <h4>Previous topic</h4> <p class="topless"><a href="select.html" title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">select</span></code> — Waiting for I/O completion</a></p> <h4>Next topic</h4> <p class="topless"><a href="asyncore.html" title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">asyncore</span></code> — Asynchronous socket handler</a></p> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/3.7/Doc/library/selectors.rst" rel="nofollow">Show Source 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