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  194.   <section id="module-selectors">

  195. <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="Link to this heading">¶</a></h1>

  196. <div class="versionadded">

  197. <p><span class="versionmodified added">New in version 3.4.</span></p>

  198. </div>

  199. <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.12/Lib/selectors.py">Lib/selectors.py</a></p>

  200. <hr class="docutils" />

  201. <section id="introduction">

  202. <h2>Introduction<a class="headerlink" href="#introduction" title="Link to this heading">¶</a></h2>

  203. <p>This module allows high-level and efficient I/O multiplexing, built upon the

  204. <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

  205. instead, unless they want precise control over the OS-level primitives used.</p>

  206. <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

  207. 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>…),

  208. that can be used to wait for I/O readiness notification on multiple file

  209. objects. In the following, “file object” refers to any object with a

  210. <a class="reference internal" href="io.html#io.IOBase.fileno" title="io.IOBase.fileno"><code class="xref py py-meth docutils literal notranslate"><span class="pre">fileno()</span></code></a> 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>

  211. <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

  212. available on the current platform: this should be the default choice for most

  213. users.</p>

  214. <div class="admonition note">

  215. <p class="admonition-title">Note</p>

  216. <p>The type of file objects supported depends on the platform: on Windows,

  217. sockets are supported, but not pipes, whereas on Unix, both are supported

  218. (some other types may be supported as well, such as fifos or special file

  219. devices).</p>

  220. </div>

  221. <div class="admonition seealso">

  222. <p class="admonition-title">See also</p>

  223. <dl class="simple">

  224. <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>

  225. </dd>

  226. </dl>

  227. </div>

  228. <div class="availability docutils container">

  229. <p><a class="reference internal" href="intro.html#availability"><span class="std std-ref">Availability</span></a>: not Emscripten, not WASI.</p>

  230. <p>This module does not work or is not available on WebAssembly platforms

  231. <code class="docutils literal notranslate"><span class="pre">wasm32-emscripten</span></code> and <code class="docutils literal notranslate"><span class="pre">wasm32-wasi</span></code>. See

  232. <a class="reference internal" href="intro.html#wasm-availability"><span class="std std-ref">WebAssembly platforms</span></a> for more information.</p>

  233. </div>

  234. </section>

  235. <section id="classes">

  236. <h2>Classes<a class="headerlink" href="#classes" title="Link to this heading">¶</a></h2>

  237. <p>Classes hierarchy:</p>

  238. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">BaseSelector</span>

  239. <span class="o">+--</span> <span class="n">SelectSelector</span>

  240. <span class="o">+--</span> <span class="n">PollSelector</span>

  241. <span class="o">+--</span> <span class="n">EpollSelector</span>

  242. <span class="o">+--</span> <span class="n">DevpollSelector</span>

  243. <span class="o">+--</span> <span class="n">KqueueSelector</span>

  244. </pre></div>

  245. </div>

  246. <p>In the following, <em>events</em> is a bitwise mask indicating which I/O events should

  247. be waited for on a given file object. It can be a combination of the modules

  248. constants below:</p>

  249. <blockquote>

  250. <div><table class="docutils align-default">

  251. <thead>

  252. <tr class="row-odd"><th class="head"><p>Constant</p></th>

  253. <th class="head"><p>Meaning</p></th>

  254. </tr>

  255. </thead>

  256. <tbody>

  257. <tr class="row-even"><td><dl class="py data">

  258. <dt class="sig sig-object py" id="selectors.EVENT_READ">

  259. <span class="sig-prename descclassname"><span class="pre">selectors.</span></span><span class="sig-name descname"><span class="pre">EVENT_READ</span></span><a class="headerlink" href="#selectors.EVENT_READ" title="Link to this definition">¶</a></dt>

  260. <dd></dd></dl>

  261. 

  262. </td>

  263. <td><p>Available for read</p></td>

  264. </tr>

  265. <tr class="row-odd"><td><dl class="py data">

  266. <dt class="sig sig-object py" id="selectors.EVENT_WRITE">

  267. <span class="sig-prename descclassname"><span class="pre">selectors.</span></span><span class="sig-name descname"><span class="pre">EVENT_WRITE</span></span><a class="headerlink" href="#selectors.EVENT_WRITE" title="Link to this definition">¶</a></dt>

  268. <dd></dd></dl>

  269. 

  270. </td>

  271. <td><p>Available for write</p></td>

  272. </tr>

  273. </tbody>

  274. </table>

  275. </div></blockquote>

  276. <dl class="py class">

  277. <dt class="sig sig-object py" id="selectors.SelectorKey">

  278. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">selectors.</span></span><span class="sig-name descname"><span class="pre">SelectorKey</span></span><a class="headerlink" href="#selectors.SelectorKey" title="Link to this definition">¶</a></dt>

  279. <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

  280. associate a file object to its underlying file descriptor, selected event

  281. 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>

  282. methods.</p>

  283. <dl class="py attribute">

  284. <dt class="sig sig-object py" id="selectors.SelectorKey.fileobj">

  285. <span class="sig-name descname"><span class="pre">fileobj</span></span><a class="headerlink" href="#selectors.SelectorKey.fileobj" title="Link to this definition">¶</a></dt>

  286. <dd><p>File object registered.</p>

  287. </dd></dl>

  288. 

  289. <dl class="py attribute">

  290. <dt class="sig sig-object py" id="selectors.SelectorKey.fd">

  291. <span class="sig-name descname"><span class="pre">fd</span></span><a class="headerlink" href="#selectors.SelectorKey.fd" title="Link to this definition">¶</a></dt>

  292. <dd><p>Underlying file descriptor.</p>

  293. </dd></dl>

  294. 

  295. <dl class="py attribute">

  296. <dt class="sig sig-object py" id="selectors.SelectorKey.events">

  297. <span class="sig-name descname"><span class="pre">events</span></span><a class="headerlink" href="#selectors.SelectorKey.events" title="Link to this definition">¶</a></dt>

  298. <dd><p>Events that must be waited for on this file object.</p>

  299. </dd></dl>

  300. 

  301. <dl class="py attribute">

  302. <dt class="sig sig-object py" id="selectors.SelectorKey.data">

  303. <span class="sig-name descname"><span class="pre">data</span></span><a class="headerlink" href="#selectors.SelectorKey.data" title="Link to this definition">¶</a></dt>

  304. <dd><p>Optional opaque data associated to this file object: for example, this

  305. could be used to store a per-client session ID.</p>

  306. </dd></dl>

  307. 

  308. </dd></dl>

  309. 

  310. <dl class="py class">

  311. <dt class="sig sig-object py" id="selectors.BaseSelector">

  312. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">selectors.</span></span><span class="sig-name descname"><span class="pre">BaseSelector</span></span><a class="headerlink" href="#selectors.BaseSelector" title="Link to this definition">¶</a></dt>

  313. <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

  314. file objects. It supports file stream registration, unregistration, and a

  315. method to wait for I/O events on those streams, with an optional timeout.

  316. It’s an abstract base class, so cannot be instantiated. Use

  317. <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>,

  318. <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

  319. implementation, and your platform supports it.

  320. <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

  321. <a class="reference internal" href="../glossary.html#term-context-manager"><span class="xref std std-term">context manager</span></a> protocol.</p>

  322. <dl class="py method">

  323. <dt class="sig sig-object py" id="selectors.BaseSelector.register">

  324. <em class="property"><span class="pre">abstractmethod</span> </em><span class="sig-name descname"><span class="pre">register</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fileobj</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">events</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">data</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.register" title="Link to this definition">¶</a></dt>

  325. <dd><p>Register a file object for selection, monitoring it for I/O events.</p>

  326. <p><em>fileobj</em> is the file object to monitor.  It may either be an integer

  327. file descriptor or an object with a <code class="docutils literal notranslate"><span class="pre">fileno()</span></code> method.

  328. <em>events</em> is a bitwise mask of events to monitor.

  329. <em>data</em> is an opaque object.</p>

  330. <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

  331. <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

  332. <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>

  333. </dd></dl>

  334. 

  335. <dl class="py method">

  336. <dt class="sig sig-object py" id="selectors.BaseSelector.unregister">

  337. <em class="property"><span class="pre">abstractmethod</span> </em><span class="sig-name descname"><span class="pre">unregister</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fileobj</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.unregister" title="Link to this definition">¶</a></dt>

  338. <dd><p>Unregister a file object from selection, removing it from monitoring. A

  339. file object shall be unregistered prior to being closed.</p>

  340. <p><em>fileobj</em> must be a file object previously registered.</p>

  341. <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

  342. <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

  343. <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>

  344. method or its <code class="docutils literal notranslate"><span class="pre">fileno()</span></code> method has an invalid return value).</p>

  345. </dd></dl>

  346. 

  347. <dl class="py method">

  348. <dt class="sig sig-object py" id="selectors.BaseSelector.modify">

  349. <span class="sig-name descname"><span class="pre">modify</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fileobj</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">events</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">data</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.modify" title="Link to this definition">¶</a></dt>

  350. <dd><p>Change a registered file object’s monitored events or attached data.</p>

  351. <p>This is equivalent to <code class="docutils literal notranslate"><span class="pre">BaseSelector.unregister(fileobj)</span></code> followed

  352. by <code class="docutils literal notranslate"><span class="pre">BaseSelector.register(fileobj,</span> <span class="pre">events,</span> <span class="pre">data)</span></code>, except that it

  353. can be implemented more efficiently.</p>

  354. <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

  355. <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

  356. <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>

  357. </dd></dl>

  358. 

  359. <dl class="py method">

  360. <dt class="sig sig-object py" id="selectors.BaseSelector.select">

  361. <em class="property"><span class="pre">abstractmethod</span> </em><span class="sig-name descname"><span class="pre">select</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">timeout</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">None</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.select" title="Link to this definition">¶</a></dt>

  362. <dd><p>Wait until some registered file objects become ready, or the timeout

  363. expires.</p>

  364. <p>If <code class="docutils literal notranslate"><span class="pre">timeout</span> <span class="pre">&gt;</span> <span class="pre">0</span></code>, this specifies the maximum wait time, in seconds.

  365. If <code class="docutils literal notranslate"><span class="pre">timeout</span> <span class="pre">&lt;=</span> <span class="pre">0</span></code>, the call won’t block, and will report the currently

  366. ready file objects.

  367. 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

  368. becomes ready.</p>

  369. <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

  370. object.</p>

  371. <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

  372. object.

  373. <em>events</em> is a bitmask of events ready on this file object.</p>

  374. <div class="admonition note">

  375. <p class="admonition-title">Note</p>

  376. <p>This method can return before any file object becomes ready or the

  377. timeout has elapsed if the current process receives a signal: in this

  378. case, an empty list will be returned.</p>

  379. </div>

  380. <div class="versionchanged">

  381. <p><span class="versionmodified changed">Changed in version 3.5: </span>The selector is now retried with a recomputed timeout when interrupted

  382. by a signal if the signal handler did not raise an exception (see

  383. <span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0475/"><strong>PEP 475</strong></a> for the rationale), instead of returning an empty list

  384. of events before the timeout.</p>

  385. </div>

  386. </dd></dl>

  387. 

  388. <dl class="py method">

  389. <dt class="sig sig-object py" id="selectors.BaseSelector.close">

  390. <span class="sig-name descname"><span class="pre">close</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.close" title="Link to this definition">¶</a></dt>

  391. <dd><p>Close the selector.</p>

  392. <p>This must be called to make sure that any underlying resource is freed.

  393. The selector shall not be used once it has been closed.</p>

  394. </dd></dl>

  395. 

  396. <dl class="py method">

  397. <dt class="sig sig-object py" id="selectors.BaseSelector.get_key">

  398. <span class="sig-name descname"><span class="pre">get_key</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fileobj</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.get_key" title="Link to this definition">¶</a></dt>

  399. <dd><p>Return the key associated with a registered file object.</p>

  400. <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

  401. 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>

  402. </dd></dl>

  403. 

  404. <dl class="py method">

  405. <dt class="sig sig-object py" id="selectors.BaseSelector.get_map">

  406. <em class="property"><span class="pre">abstractmethod</span> </em><span class="sig-name descname"><span class="pre">get_map</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#selectors.BaseSelector.get_map" title="Link to this definition">¶</a></dt>

  407. <dd><p>Return a mapping of file objects to selector keys.</p>

  408. <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

  409. 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>

  410. instance.</p>

  411. </dd></dl>

  412. 

  413. </dd></dl>

  414. 

  415. <dl class="py class">

  416. <dt class="sig sig-object py" id="selectors.DefaultSelector">

  417. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">selectors.</span></span><span class="sig-name descname"><span class="pre">DefaultSelector</span></span><a class="headerlink" href="#selectors.DefaultSelector" title="Link to this definition">¶</a></dt>

  418. <dd><p>The default selector class, using the most efficient implementation

  419. available on the current platform. This should be the default choice for

  420. most users.</p>

  421. </dd></dl>

  422. 

  423. <dl class="py class">

  424. <dt class="sig sig-object py" id="selectors.SelectSelector">

  425. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">selectors.</span></span><span class="sig-name descname"><span class="pre">SelectSelector</span></span><a class="headerlink" href="#selectors.SelectSelector" title="Link to this definition">¶</a></dt>

  426. <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>

  427. </dd></dl>

  428. 

  429. <dl class="py class">

  430. <dt class="sig sig-object py" id="selectors.PollSelector">

  431. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">selectors.</span></span><span class="sig-name descname"><span class="pre">PollSelector</span></span><a class="headerlink" href="#selectors.PollSelector" title="Link to this definition">¶</a></dt>

  432. <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>

  433. </dd></dl>

  434. 

  435. <dl class="py class">

  436. <dt class="sig sig-object py" id="selectors.EpollSelector">

  437. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">selectors.</span></span><span class="sig-name descname"><span class="pre">EpollSelector</span></span><a class="headerlink" href="#selectors.EpollSelector" title="Link to this definition">¶</a></dt>

  438. <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>

  439. <dl class="py method">

  440. <dt class="sig sig-object py" id="selectors.EpollSelector.fileno">

  441. <span class="sig-name descname"><span class="pre">fileno</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#selectors.EpollSelector.fileno" title="Link to this definition">¶</a></dt>

  442. <dd><p>This returns the file descriptor used by the underlying

  443. <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>

  444. </dd></dl>

  445. 

  446. </dd></dl>

  447. 

  448. <dl class="py class">

  449. <dt class="sig sig-object py" id="selectors.DevpollSelector">

  450. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">selectors.</span></span><span class="sig-name descname"><span class="pre">DevpollSelector</span></span><a class="headerlink" href="#selectors.DevpollSelector" title="Link to this definition">¶</a></dt>

  451. <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>

  452. <dl class="py method">

  453. <dt class="sig sig-object py" id="selectors.DevpollSelector.fileno">

  454. <span class="sig-name descname"><span class="pre">fileno</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#selectors.DevpollSelector.fileno" title="Link to this definition">¶</a></dt>

  455. <dd><p>This returns the file descriptor used by the underlying

  456. <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>

  457. </dd></dl>

  458. 

  459. <div class="versionadded">

  460. <p><span class="versionmodified added">New in version 3.5.</span></p>

  461. </div>

  462. </dd></dl>

  463. 

  464. <dl class="py class">

  465. <dt class="sig sig-object py" id="selectors.KqueueSelector">

  466. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">selectors.</span></span><span class="sig-name descname"><span class="pre">KqueueSelector</span></span><a class="headerlink" href="#selectors.KqueueSelector" title="Link to this definition">¶</a></dt>

  467. <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>

  468. <dl class="py method">

  469. <dt class="sig sig-object py" id="selectors.KqueueSelector.fileno">

  470. <span class="sig-name descname"><span class="pre">fileno</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#selectors.KqueueSelector.fileno" title="Link to this definition">¶</a></dt>

  471. <dd><p>This returns the file descriptor used by the underlying

  472. <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>

  473. </dd></dl>

  474. 

  475. </dd></dl>

  476. 

  477. </section>

  478. <section id="examples">

  479. <h2>Examples<a class="headerlink" href="#examples" title="Link to this heading">¶</a></h2>

  480. <p>Here is a simple echo server implementation:</p>

  481. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">import</span> <span class="nn">selectors</span>

  482. <span class="kn">import</span> <span class="nn">socket</span>

  483. 

  484. <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>

  485. 

  486. <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>

  487.     <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>

  488.     <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;accepted&#39;</span><span class="p">,</span> <span class="n">conn</span><span class="p">,</span> <span class="s1">&#39;from&#39;</span><span class="p">,</span> <span class="n">addr</span><span class="p">)</span>

  489.     <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>

  490.     <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>

  491. 

  492. <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>

  493.     <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>

  494.     <span class="k">if</span> <span class="n">data</span><span class="p">:</span>

  495.         <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;echoing&#39;</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">&#39;to&#39;</span><span class="p">,</span> <span class="n">conn</span><span class="p">)</span>

  496.         <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&#39;t block</span>

  497.     <span class="k">else</span><span class="p">:</span>

  498.         <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;closing&#39;</span><span class="p">,</span> <span class="n">conn</span><span class="p">)</span>

  499.         <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>

  500.         <span class="n">conn</span><span class="o">.</span><span class="n">close</span><span class="p">()</span>

  501. 

  502. <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>

  503. <span class="n">sock</span><span class="o">.</span><span class="n">bind</span><span class="p">((</span><span class="s1">&#39;localhost&#39;</span><span class="p">,</span> <span class="mi">1234</span><span class="p">))</span>

  504. <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>

  505. <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>

  506. <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>

  507. 

  508. <span class="k">while</span> <span class="kc">True</span><span class="p">:</span>

  509.     <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>

  510.     <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>

  511.         <span class="n">callback</span> <span class="o">=</span> <span class="n">key</span><span class="o">.</span><span class="n">data</span>

  512.         <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>

  513. </pre></div>

  514. </div>

  515. </section>

  516. </section>

  517. 

  518. 

  519.             <div class="clearer"></div>

  520.           </div>

  521.         </div>

  522.       </div>

  523.       <div class="sphinxsidebar" role="navigation" aria-label="main navigation">

  524.         <div class="sphinxsidebarwrapper">

  525.   <div>

  526.     <h3><a href="../contents.html">Table of Contents</a></h3>

  527.     <ul>

  528. <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>

  529. <li><a class="reference internal" href="#introduction">Introduction</a></li>

  530. <li><a class="reference internal" href="#classes">Classes</a></li>

  531. <li><a class="reference internal" href="#examples">Examples</a></li>

  532. </ul>

  533. </li>

  534. </ul>

  535. 

  536.   </div>

  537.   <div>

  538.     <h4>Previous topic</h4>

  539.     <p class="topless"><a href="select.html"

  540.                           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>

  541.   </div>

  542.   <div>

  543.     <h4>Next topic</h4>

  544.     <p class="topless"><a href="signal.html"

  545.                           title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">signal</span></code> — Set handlers for asynchronous events</a></p>

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