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  193.   <section id="module-queue">

  194. <span id="queue-a-synchronized-queue-class"></span><h1><a class="reference internal" href="#module-queue" title="queue: A synchronized queue class."><code class="xref py py-mod docutils literal notranslate"><span class="pre">queue</span></code></a> — A synchronized queue class<a class="headerlink" href="#module-queue" title="Link to this heading">¶</a></h1>

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

  196. <hr class="docutils" />

  197. <p>The <a class="reference internal" href="#module-queue" title="queue: A synchronized queue class."><code class="xref py py-mod docutils literal notranslate"><span class="pre">queue</span></code></a> module implements multi-producer, multi-consumer queues.

  198. It is especially useful in threaded programming when information must be

  199. exchanged safely between multiple threads.  The <a class="reference internal" href="#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a> class in this

  200. module implements all the required locking semantics.</p>

  201. <p>The module implements three types of queue, which differ only in the order in

  202. which the entries are retrieved.  In a <abbr title="first-in, first-out">FIFO</abbr>

  203. queue, the first tasks added are the first retrieved.  In a

  204. <abbr title="last-in, first-out">LIFO</abbr> queue, the most recently added entry is

  205. the first retrieved (operating like a stack).  With a priority queue,

  206. the entries are kept sorted (using the <a class="reference internal" href="heapq.html#module-heapq" title="heapq: Heap queue algorithm (a.k.a. priority queue)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">heapq</span></code></a> module) and the

  207. lowest valued entry is retrieved first.</p>

  208. <p>Internally, those three types of queues use locks to temporarily block

  209. competing threads; however, they are not designed to handle reentrancy

  210. within a thread.</p>

  211. <p>In addition, the module implements a “simple”

  212. <abbr title="first-in, first-out">FIFO</abbr> queue type, <a class="reference internal" href="#queue.SimpleQueue" title="queue.SimpleQueue"><code class="xref py py-class docutils literal notranslate"><span class="pre">SimpleQueue</span></code></a>, whose

  213. specific implementation provides additional guarantees

  214. in exchange for the smaller functionality.</p>

  215. <p>The <a class="reference internal" href="#module-queue" title="queue: A synchronized queue class."><code class="xref py py-mod docutils literal notranslate"><span class="pre">queue</span></code></a> module defines the following classes and exceptions:</p>

  216. <dl class="py class">

  217. <dt class="sig sig-object py" id="queue.Queue">

  218. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">queue.</span></span><span class="sig-name descname"><span class="pre">Queue</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">maxsize</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue" title="Link to this definition">¶</a></dt>

  219. <dd><p>Constructor for a <abbr title="first-in, first-out">FIFO</abbr> queue.  <em>maxsize</em> is

  220. an integer that sets the upperbound

  221. limit on the number of items that can be placed in the queue.  Insertion will

  222. block once this size has been reached, until queue items are consumed.  If

  223. <em>maxsize</em> is less than or equal to zero, the queue size is infinite.</p>

  224. </dd></dl>

  225. 

  226. <dl class="py class">

  227. <dt class="sig sig-object py" id="queue.LifoQueue">

  228. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">queue.</span></span><span class="sig-name descname"><span class="pre">LifoQueue</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">maxsize</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.LifoQueue" title="Link to this definition">¶</a></dt>

  229. <dd><p>Constructor for a <abbr title="last-in, first-out">LIFO</abbr> queue.  <em>maxsize</em> is

  230. an integer that sets the upperbound

  231. limit on the number of items that can be placed in the queue.  Insertion will

  232. block once this size has been reached, until queue items are consumed.  If

  233. <em>maxsize</em> is less than or equal to zero, the queue size is infinite.</p>

  234. </dd></dl>

  235. 

  236. <dl class="py class">

  237. <dt class="sig sig-object py" id="queue.PriorityQueue">

  238. <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">queue.</span></span><span class="sig-name descname"><span class="pre">PriorityQueue</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">maxsize</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">0</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.PriorityQueue" title="Link to this definition">¶</a></dt>

  239. <dd><p>Constructor for a priority queue.  <em>maxsize</em> is an integer that sets the upperbound

  240. limit on the number of items that can be placed in the queue.  Insertion will

  241. block once this size has been reached, until queue items are consumed.  If

  242. <em>maxsize</em> is less than or equal to zero, the queue size is infinite.</p>

  243. <p>The lowest valued entries are retrieved first (the lowest valued entry is the

  244. one that would be returned by <code class="docutils literal notranslate"><span class="pre">min(entries)</span></code>).  A typical pattern for

  245. entries is a tuple in the form: <code class="docutils literal notranslate"><span class="pre">(priority_number,</span> <span class="pre">data)</span></code>.</p>

  246. <p>If the <em>data</em> elements are not comparable, the data can be wrapped in a class

  247. that ignores the data item and only compares the priority number:</p>

  248. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">dataclasses</span> <span class="kn">import</span> <span class="n">dataclass</span><span class="p">,</span> <span class="n">field</span>

  249. <span class="kn">from</span> <span class="nn">typing</span> <span class="kn">import</span> <span class="n">Any</span>

  250. 

  251. <span class="nd">@dataclass</span><span class="p">(</span><span class="n">order</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span>

  252. <span class="k">class</span> <span class="nc">PrioritizedItem</span><span class="p">:</span>

  253.     <span class="n">priority</span><span class="p">:</span> <span class="nb">int</span>

  254.     <span class="n">item</span><span class="p">:</span> <span class="n">Any</span><span class="o">=</span><span class="n">field</span><span class="p">(</span><span class="n">compare</span><span class="o">=</span><span class="kc">False</span><span class="p">)</span>

  255. </pre></div>

  256. </div>

  257. </dd></dl>

  258. 

  259. <dl class="py class">

  260. <dt class="sig sig-object py" id="queue.SimpleQueue">

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

  262. <dd><p>Constructor for an unbounded <abbr title="first-in, first-out">FIFO</abbr> queue.

  263. Simple queues lack advanced functionality such as task tracking.</p>

  264. <div class="versionadded">

  265. <p><span class="versionmodified added">New in version 3.7.</span></p>

  266. </div>

  267. </dd></dl>

  268. 

  269. <dl class="py exception">

  270. <dt class="sig sig-object py" id="queue.Empty">

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

  272. <dd><p>Exception raised when non-blocking <a class="reference internal" href="#queue.Queue.get" title="queue.Queue.get"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get()</span></code></a> (or

  273. <a class="reference internal" href="#queue.Queue.get_nowait" title="queue.Queue.get_nowait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get_nowait()</span></code></a>) is called

  274. on a <a class="reference internal" href="#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a> object which is empty.</p>

  275. </dd></dl>

  276. 

  277. <dl class="py exception">

  278. <dt class="sig sig-object py" id="queue.Full">

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

  280. <dd><p>Exception raised when non-blocking <a class="reference internal" href="#queue.Queue.put" title="queue.Queue.put"><code class="xref py py-meth docutils literal notranslate"><span class="pre">put()</span></code></a> (or

  281. <a class="reference internal" href="#queue.Queue.put_nowait" title="queue.Queue.put_nowait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">put_nowait()</span></code></a>) is called

  282. on a <a class="reference internal" href="#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a> object which is full.</p>

  283. </dd></dl>

  284. 

  285. <section id="queue-objects">

  286. <span id="queueobjects"></span><h2>Queue Objects<a class="headerlink" href="#queue-objects" title="Link to this heading">¶</a></h2>

  287. <p>Queue objects (<a class="reference internal" href="#queue.Queue" title="queue.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">Queue</span></code></a>, <a class="reference internal" href="#queue.LifoQueue" title="queue.LifoQueue"><code class="xref py py-class docutils literal notranslate"><span class="pre">LifoQueue</span></code></a>, or <a class="reference internal" href="#queue.PriorityQueue" title="queue.PriorityQueue"><code class="xref py py-class docutils literal notranslate"><span class="pre">PriorityQueue</span></code></a>)

  288. provide the public methods described below.</p>

  289. <dl class="py method">

  290. <dt class="sig sig-object py" id="queue.Queue.qsize">

  291. <span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">qsize</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.qsize" title="Link to this definition">¶</a></dt>

  292. <dd><p>Return the approximate size of the queue.  Note, qsize() &gt; 0 doesn’t

  293. guarantee that a subsequent get() will not block, nor will qsize() &lt; maxsize

  294. guarantee that put() will not block.</p>

  295. </dd></dl>

  296. 

  297. <dl class="py method">

  298. <dt class="sig sig-object py" id="queue.Queue.empty">

  299. <span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">empty</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.empty" title="Link to this definition">¶</a></dt>

  300. <dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the queue is empty, <code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise.  If empty()

  301. returns <code class="docutils literal notranslate"><span class="pre">True</span></code> it doesn’t guarantee that a subsequent call to put()

  302. will not block.  Similarly, if empty() returns <code class="docutils literal notranslate"><span class="pre">False</span></code> it doesn’t

  303. guarantee that a subsequent call to get() will not block.</p>

  304. </dd></dl>

  305. 

  306. <dl class="py method">

  307. <dt class="sig sig-object py" id="queue.Queue.full">

  308. <span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">full</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.full" title="Link to this definition">¶</a></dt>

  309. <dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the queue is full, <code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise.  If full()

  310. returns <code class="docutils literal notranslate"><span class="pre">True</span></code> it doesn’t guarantee that a subsequent call to get()

  311. will not block.  Similarly, if full() returns <code class="docutils literal notranslate"><span class="pre">False</span></code> it doesn’t

  312. guarantee that a subsequent call to put() will not block.</p>

  313. </dd></dl>

  314. 

  315. <dl class="py method">

  316. <dt class="sig sig-object py" id="queue.Queue.put">

  317. <span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">put</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">item</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">block</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em>, <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="#queue.Queue.put" title="Link to this definition">¶</a></dt>

  318. <dd><p>Put <em>item</em> into the queue.  If optional args <em>block</em> is true and <em>timeout</em> is

  319. <code class="docutils literal notranslate"><span class="pre">None</span></code> (the default), block if necessary until a free slot is available.  If

  320. <em>timeout</em> is a positive number, it blocks at most <em>timeout</em> seconds and raises

  321. the <a class="reference internal" href="#queue.Full" title="queue.Full"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Full</span></code></a> exception if no free slot was available within that time.

  322. Otherwise (<em>block</em> is false), put an item on the queue if a free slot is

  323. immediately available, else raise the <a class="reference internal" href="#queue.Full" title="queue.Full"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Full</span></code></a> exception (<em>timeout</em> is

  324. ignored in that case).</p>

  325. </dd></dl>

  326. 

  327. <dl class="py method">

  328. <dt class="sig sig-object py" id="queue.Queue.put_nowait">

  329. <span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">put_nowait</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">item</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.put_nowait" title="Link to this definition">¶</a></dt>

  330. <dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">put(item,</span> <span class="pre">block=False)</span></code>.</p>

  331. </dd></dl>

  332. 

  333. <dl class="py method">

  334. <dt class="sig sig-object py" id="queue.Queue.get">

  335. <span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">get</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">block</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em>, <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="#queue.Queue.get" title="Link to this definition">¶</a></dt>

  336. <dd><p>Remove and return an item from the queue.  If optional args <em>block</em> is true and

  337. <em>timeout</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code> (the default), block if necessary until an item is available.

  338. If <em>timeout</em> is a positive number, it blocks at most <em>timeout</em> seconds and

  339. raises the <a class="reference internal" href="#queue.Empty" title="queue.Empty"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Empty</span></code></a> exception if no item was available within that time.

  340. Otherwise (<em>block</em> is false), return an item if one is immediately available,

  341. else raise the <a class="reference internal" href="#queue.Empty" title="queue.Empty"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Empty</span></code></a> exception (<em>timeout</em> is ignored in that case).</p>

  342. <p>Prior to 3.0 on POSIX systems, and for all versions on Windows, if

  343. <em>block</em> is true and <em>timeout</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code>, this operation goes into

  344. an uninterruptible wait on an underlying lock.  This means that no exceptions

  345. can occur, and in particular a SIGINT will not trigger a <a class="reference internal" href="exceptions.html#KeyboardInterrupt" title="KeyboardInterrupt"><code class="xref py py-exc docutils literal notranslate"><span class="pre">KeyboardInterrupt</span></code></a>.</p>

  346. </dd></dl>

  347. 

  348. <dl class="py method">

  349. <dt class="sig sig-object py" id="queue.Queue.get_nowait">

  350. <span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">get_nowait</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.get_nowait" title="Link to this definition">¶</a></dt>

  351. <dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">get(False)</span></code>.</p>

  352. </dd></dl>

  353. 

  354. <p>Two methods are offered to support tracking whether enqueued tasks have been

  355. fully processed by daemon consumer threads.</p>

  356. <dl class="py method">

  357. <dt class="sig sig-object py" id="queue.Queue.task_done">

  358. <span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">task_done</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.task_done" title="Link to this definition">¶</a></dt>

  359. <dd><p>Indicate that a formerly enqueued task is complete.  Used by queue consumer

  360. threads.  For each <a class="reference internal" href="#queue.Queue.get" title="queue.Queue.get"><code class="xref py py-meth docutils literal notranslate"><span class="pre">get()</span></code></a> used to fetch a task, a subsequent call to

  361. <a class="reference internal" href="#queue.Queue.task_done" title="queue.Queue.task_done"><code class="xref py py-meth docutils literal notranslate"><span class="pre">task_done()</span></code></a> tells the queue that the processing on the task is complete.</p>

  362. <p>If a <a class="reference internal" href="#queue.Queue.join" title="queue.Queue.join"><code class="xref py py-meth docutils literal notranslate"><span class="pre">join()</span></code></a> is currently blocking, it will resume when all items have been

  363. processed (meaning that a <a class="reference internal" href="#queue.Queue.task_done" title="queue.Queue.task_done"><code class="xref py py-meth docutils literal notranslate"><span class="pre">task_done()</span></code></a> call was received for every item

  364. that had been <a class="reference internal" href="#queue.Queue.put" title="queue.Queue.put"><code class="xref py py-meth docutils literal notranslate"><span class="pre">put()</span></code></a> into the queue).</p>

  365. <p>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> if called more times than there were items placed in

  366. the queue.</p>

  367. </dd></dl>

  368. 

  369. <dl class="py method">

  370. <dt class="sig sig-object py" id="queue.Queue.join">

  371. <span class="sig-prename descclassname"><span class="pre">Queue.</span></span><span class="sig-name descname"><span class="pre">join</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.join" title="Link to this definition">¶</a></dt>

  372. <dd><p>Blocks until all items in the queue have been gotten and processed.</p>

  373. <p>The count of unfinished tasks goes up whenever an item is added to the queue.

  374. The count goes down whenever a consumer thread calls <a class="reference internal" href="#queue.Queue.task_done" title="queue.Queue.task_done"><code class="xref py py-meth docutils literal notranslate"><span class="pre">task_done()</span></code></a> to

  375. indicate that the item was retrieved and all work on it is complete.  When the

  376. count of unfinished tasks drops to zero, <a class="reference internal" href="#queue.Queue.join" title="queue.Queue.join"><code class="xref py py-meth docutils literal notranslate"><span class="pre">join()</span></code></a> unblocks.</p>

  377. </dd></dl>

  378. 

  379. <p>Example of how to wait for enqueued tasks to be completed:</p>

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

  381. <span class="kn">import</span> <span class="nn">queue</span>

  382. 

  383. <span class="n">q</span> <span class="o">=</span> <span class="n">queue</span><span class="o">.</span><span class="n">Queue</span><span class="p">()</span>

  384. 

  385. <span class="k">def</span> <span class="nf">worker</span><span class="p">():</span>

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

  387.         <span class="n">item</span> <span class="o">=</span> <span class="n">q</span><span class="o">.</span><span class="n">get</span><span class="p">()</span>

  388.         <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;Working on </span><span class="si">{</span><span class="n">item</span><span class="si">}</span><span class="s1">&#39;</span><span class="p">)</span>

  389.         <span class="nb">print</span><span class="p">(</span><span class="sa">f</span><span class="s1">&#39;Finished </span><span class="si">{</span><span class="n">item</span><span class="si">}</span><span class="s1">&#39;</span><span class="p">)</span>

  390.         <span class="n">q</span><span class="o">.</span><span class="n">task_done</span><span class="p">()</span>

  391. 

  392. <span class="c1"># Turn-on the worker thread.</span>

  393. <span class="n">threading</span><span class="o">.</span><span class="n">Thread</span><span class="p">(</span><span class="n">target</span><span class="o">=</span><span class="n">worker</span><span class="p">,</span> <span class="n">daemon</span><span class="o">=</span><span class="kc">True</span><span class="p">)</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>

  394. 

  395. <span class="c1"># Send thirty task requests to the worker.</span>

  396. <span class="k">for</span> <span class="n">item</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">30</span><span class="p">):</span>

  397.     <span class="n">q</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="n">item</span><span class="p">)</span>

  398. 

  399. <span class="c1"># Block until all tasks are done.</span>

  400. <span class="n">q</span><span class="o">.</span><span class="n">join</span><span class="p">()</span>

  401. <span class="nb">print</span><span class="p">(</span><span class="s1">&#39;All work completed&#39;</span><span class="p">)</span>

  402. </pre></div>

  403. </div>

  404. </section>

  405. <section id="simplequeue-objects">

  406. <h2>SimpleQueue Objects<a class="headerlink" href="#simplequeue-objects" title="Link to this heading">¶</a></h2>

  407. <p><a class="reference internal" href="#queue.SimpleQueue" title="queue.SimpleQueue"><code class="xref py py-class docutils literal notranslate"><span class="pre">SimpleQueue</span></code></a> objects provide the public methods described below.</p>

  408. <dl class="py method">

  409. <dt class="sig sig-object py" id="queue.SimpleQueue.qsize">

  410. <span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">qsize</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.qsize" title="Link to this definition">¶</a></dt>

  411. <dd><p>Return the approximate size of the queue.  Note, qsize() &gt; 0 doesn’t

  412. guarantee that a subsequent get() will not block.</p>

  413. </dd></dl>

  414. 

  415. <dl class="py method">

  416. <dt class="sig sig-object py" id="queue.SimpleQueue.empty">

  417. <span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">empty</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.empty" title="Link to this definition">¶</a></dt>

  418. <dd><p>Return <code class="docutils literal notranslate"><span class="pre">True</span></code> if the queue is empty, <code class="docutils literal notranslate"><span class="pre">False</span></code> otherwise.  If empty()

  419. returns <code class="docutils literal notranslate"><span class="pre">False</span></code> it doesn’t guarantee that a subsequent call to get()

  420. will not block.</p>

  421. </dd></dl>

  422. 

  423. <dl class="py method">

  424. <dt class="sig sig-object py" id="queue.SimpleQueue.put">

  425. <span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">put</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">item</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">block</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em>, <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="#queue.SimpleQueue.put" title="Link to this definition">¶</a></dt>

  426. <dd><p>Put <em>item</em> into the queue.  The method never blocks and always succeeds

  427. (except for potential low-level errors such as failure to allocate memory).

  428. The optional args <em>block</em> and <em>timeout</em> are ignored and only provided

  429. for compatibility with <a class="reference internal" href="#queue.Queue.put" title="queue.Queue.put"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Queue.put()</span></code></a>.</p>

  430. <div class="impl-detail compound">

  431. <p><strong>CPython implementation detail:</strong> This method has a C implementation which is reentrant.  That is, a

  432. <code class="docutils literal notranslate"><span class="pre">put()</span></code> or <code class="docutils literal notranslate"><span class="pre">get()</span></code> call can be interrupted by another <code class="docutils literal notranslate"><span class="pre">put()</span></code>

  433. call in the same thread without deadlocking or corrupting internal

  434. state inside the queue.  This makes it appropriate for use in

  435. destructors such as <code class="docutils literal notranslate"><span class="pre">__del__</span></code> methods or <a class="reference internal" href="weakref.html#module-weakref" title="weakref: Support for weak references and weak dictionaries."><code class="xref py py-mod docutils literal notranslate"><span class="pre">weakref</span></code></a> callbacks.</p>

  436. </div>

  437. </dd></dl>

  438. 

  439. <dl class="py method">

  440. <dt class="sig sig-object py" id="queue.SimpleQueue.put_nowait">

  441. <span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">put_nowait</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">item</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.put_nowait" title="Link to this definition">¶</a></dt>

  442. <dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">put(item,</span> <span class="pre">block=False)</span></code>, provided for compatibility with

  443. <a class="reference internal" href="#queue.Queue.put_nowait" title="queue.Queue.put_nowait"><code class="xref py py-meth docutils literal notranslate"><span class="pre">Queue.put_nowait()</span></code></a>.</p>

  444. </dd></dl>

  445. 

  446. <dl class="py method">

  447. <dt class="sig sig-object py" id="queue.SimpleQueue.get">

  448. <span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">get</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">block</span></span><span class="o"><span class="pre">=</span></span><span class="default_value"><span class="pre">True</span></span></em>, <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="#queue.SimpleQueue.get" title="Link to this definition">¶</a></dt>

  449. <dd><p>Remove and return an item from the queue.  If optional args <em>block</em> is true and

  450. <em>timeout</em> is <code class="docutils literal notranslate"><span class="pre">None</span></code> (the default), block if necessary until an item is available.

  451. If <em>timeout</em> is a positive number, it blocks at most <em>timeout</em> seconds and

  452. raises the <a class="reference internal" href="#queue.Empty" title="queue.Empty"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Empty</span></code></a> exception if no item was available within that time.

  453. Otherwise (<em>block</em> is false), return an item if one is immediately available,

  454. else raise the <a class="reference internal" href="#queue.Empty" title="queue.Empty"><code class="xref py py-exc docutils literal notranslate"><span class="pre">Empty</span></code></a> exception (<em>timeout</em> is ignored in that case).</p>

  455. </dd></dl>

  456. 

  457. <dl class="py method">

  458. <dt class="sig sig-object py" id="queue.SimpleQueue.get_nowait">

  459. <span class="sig-prename descclassname"><span class="pre">SimpleQueue.</span></span><span class="sig-name descname"><span class="pre">get_nowait</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.get_nowait" title="Link to this definition">¶</a></dt>

  460. <dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">get(False)</span></code>.</p>

  461. </dd></dl>

  462. 

  463. <div class="admonition seealso">

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

  465. <dl class="simple">

  466. <dt>Class <a class="reference internal" href="multiprocessing.html#multiprocessing.Queue" title="multiprocessing.Queue"><code class="xref py py-class docutils literal notranslate"><span class="pre">multiprocessing.Queue</span></code></a></dt><dd><p>A queue class for use in a multi-processing (rather than multi-threading)

  467. context.</p>

  468. </dd>

  469. </dl>

  470. <p><a class="reference internal" href="collections.html#collections.deque" title="collections.deque"><code class="xref py py-class docutils literal notranslate"><span class="pre">collections.deque</span></code></a> is an alternative implementation of unbounded

  471. queues with fast atomic <a class="reference internal" href="collections.html#collections.deque.append" title="collections.deque.append"><code class="xref py py-meth docutils literal notranslate"><span class="pre">append()</span></code></a> and

  472. <a class="reference internal" href="collections.html#collections.deque.popleft" title="collections.deque.popleft"><code class="xref py py-meth docutils literal notranslate"><span class="pre">popleft()</span></code></a> operations that do not require locking

  473. and also support indexing.</p>

  474. </div>

  475. </section>

  476. </section>

  477. 

  478. 

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  487.     <ul>

  488. <li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">queue</span></code> — A synchronized queue class</a><ul>

  489. <li><a class="reference internal" href="#queue-objects">Queue Objects</a></li>

  490. <li><a class="reference internal" href="#simplequeue-objects">SimpleQueue Objects</a></li>

  491. </ul>

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