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<div class="section" id="module-queue">
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<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="Permalink to this headline">¶</a></h1>
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<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/queue.py">Lib/queue.py</a></p>
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<hr class="docutils" />
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<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.
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It is especially useful in threaded programming when information must be
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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
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module implements all the required locking semantics. It depends on the
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availability of thread support in Python; see the <a class="reference internal" href="threading.html#module-threading" title="threading: Thread-based parallelism."><code class="xref py py-mod docutils literal notranslate"><span class="pre">threading</span></code></a>
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module.</p>
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<p>The module implements three types of queue, which differ only in the order in
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which the entries are retrieved. In a <abbr title="first-in, first-out">FIFO</abbr>
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queue, the first tasks added are the first retrieved. In a
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<abbr title="last-in, first-out">LIFO</abbr> queue, the most recently added entry is
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the first retrieved (operating like a stack). With a priority queue,
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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
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lowest valued entry is retrieved first.</p>
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<p>Internally, those three types of queues use locks to temporarily block
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competing threads; however, they are not designed to handle reentrancy
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within a thread.</p>
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<p>In addition, the module implements a “simple”
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<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
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specific implementation provides additional guarantees
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in exchange for the smaller functionality.</p>
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<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>
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<dl class="class">
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<dt id="queue.Queue">
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<em class="property">class </em><code class="descclassname">queue.</code><code class="descname">Queue</code><span class="sig-paren">(</span><em>maxsize=0</em><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue" title="Permalink to this definition">¶</a></dt>
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<dd><p>Constructor for a <abbr title="first-in, first-out">FIFO</abbr> queue. <em>maxsize</em> is
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an integer that sets the upperbound
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limit on the number of items that can be placed in the queue. Insertion will
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block once this size has been reached, until queue items are consumed. If
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<em>maxsize</em> is less than or equal to zero, the queue size is infinite.</p>
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</dd></dl>
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<dl class="class">
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<dt id="queue.LifoQueue">
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<em class="property">class </em><code class="descclassname">queue.</code><code class="descname">LifoQueue</code><span class="sig-paren">(</span><em>maxsize=0</em><span class="sig-paren">)</span><a class="headerlink" href="#queue.LifoQueue" title="Permalink to this definition">¶</a></dt>
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<dd><p>Constructor for a <abbr title="last-in, first-out">LIFO</abbr> queue. <em>maxsize</em> is
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an integer that sets the upperbound
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limit on the number of items that can be placed in the queue. Insertion will
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block once this size has been reached, until queue items are consumed. If
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<em>maxsize</em> is less than or equal to zero, the queue size is infinite.</p>
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</dd></dl>
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<dl class="class">
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<dt id="queue.PriorityQueue">
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<em class="property">class </em><code class="descclassname">queue.</code><code class="descname">PriorityQueue</code><span class="sig-paren">(</span><em>maxsize=0</em><span class="sig-paren">)</span><a class="headerlink" href="#queue.PriorityQueue" title="Permalink to this definition">¶</a></dt>
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<dd><p>Constructor for a priority queue. <em>maxsize</em> is an integer that sets the upperbound
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limit on the number of items that can be placed in the queue. Insertion will
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block once this size has been reached, until queue items are consumed. If
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<em>maxsize</em> is less than or equal to zero, the queue size is infinite.</p>
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<p>The lowest valued entries are retrieved first (the lowest valued entry is the
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one returned by <code class="docutils literal notranslate"><span class="pre">sorted(list(entries))[0]</span></code>). A typical pattern for entries
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is a tuple in the form: <code class="docutils literal notranslate"><span class="pre">(priority_number,</span> <span class="pre">data)</span></code>.</p>
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<p>If the <em>data</em> elements are not comparable, the data can be wrapped in a class
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that ignores the data item and only compares the priority number:</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">dataclasses</span> <span class="k">import</span> <span class="n">dataclass</span><span class="p">,</span> <span class="n">field</span>
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<span class="kn">from</span> <span class="nn">typing</span> <span class="k">import</span> <span class="n">Any</span>
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<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>
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<span class="k">class</span> <span class="nc">PrioritizedItem</span><span class="p">:</span>
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<span class="n">priority</span><span class="p">:</span> <span class="nb">int</span>
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<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>
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</pre></div>
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</div>
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</dd></dl>
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<dl class="class">
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<dt id="queue.SimpleQueue">
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<em class="property">class </em><code class="descclassname">queue.</code><code class="descname">SimpleQueue</code><a class="headerlink" href="#queue.SimpleQueue" title="Permalink to this definition">¶</a></dt>
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<dd><p>Constructor for an unbounded <abbr title="first-in, first-out">FIFO</abbr> queue.
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Simple queues lack advanced functionality such as task tracking.</p>
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<div class="versionadded">
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<p><span class="versionmodified added">New in version 3.7.</span></p>
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</div>
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</dd></dl>
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<dl class="exception">
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<dt id="queue.Empty">
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<em class="property">exception </em><code class="descclassname">queue.</code><code class="descname">Empty</code><a class="headerlink" href="#queue.Empty" title="Permalink to this definition">¶</a></dt>
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<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
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<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
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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>
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</dd></dl>
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<dl class="exception">
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<dt id="queue.Full">
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<em class="property">exception </em><code class="descclassname">queue.</code><code class="descname">Full</code><a class="headerlink" href="#queue.Full" title="Permalink to this definition">¶</a></dt>
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<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
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<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
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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>
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</dd></dl>
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<div class="section" id="queue-objects">
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<span id="queueobjects"></span><h2>Queue Objects<a class="headerlink" href="#queue-objects" title="Permalink to this headline">¶</a></h2>
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<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>)
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provide the public methods described below.</p>
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<dl class="method">
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<dt id="queue.Queue.qsize">
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<code class="descclassname">Queue.</code><code class="descname">qsize</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.qsize" title="Permalink to this definition">¶</a></dt>
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<dd><p>Return the approximate size of the queue. Note, qsize() > 0 doesn’t
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guarantee that a subsequent get() will not block, nor will qsize() < maxsize
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guarantee that put() will not block.</p>
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</dd></dl>
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<dl class="method">
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<dt id="queue.Queue.empty">
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<code class="descclassname">Queue.</code><code class="descname">empty</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.empty" title="Permalink to this definition">¶</a></dt>
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<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()
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returns <code class="docutils literal notranslate"><span class="pre">True</span></code> it doesn’t guarantee that a subsequent call to put()
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will not block. Similarly, if empty() returns <code class="docutils literal notranslate"><span class="pre">False</span></code> it doesn’t
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guarantee that a subsequent call to get() will not block.</p>
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</dd></dl>
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<dl class="method">
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<dt id="queue.Queue.full">
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<code class="descclassname">Queue.</code><code class="descname">full</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.full" title="Permalink to this definition">¶</a></dt>
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<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()
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returns <code class="docutils literal notranslate"><span class="pre">True</span></code> it doesn’t guarantee that a subsequent call to get()
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will not block. Similarly, if full() returns <code class="docutils literal notranslate"><span class="pre">False</span></code> it doesn’t
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guarantee that a subsequent call to put() will not block.</p>
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</dd></dl>
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<dl class="method">
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<dt id="queue.Queue.put">
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<code class="descclassname">Queue.</code><code class="descname">put</code><span class="sig-paren">(</span><em>item</em>, <em>block=True</em>, <em>timeout=None</em><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.put" title="Permalink to this definition">¶</a></dt>
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<dd><p>Put <em>item</em> into the queue. If optional args <em>block</em> is true and <em>timeout</em> is
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<code class="docutils literal notranslate"><span class="pre">None</span></code> (the default), block if necessary until a free slot is available. If
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<em>timeout</em> is a positive number, it blocks at most <em>timeout</em> seconds and raises
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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.
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Otherwise (<em>block</em> is false), put an item on the queue if a free slot is
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|
|
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
|
|||
|
|
ignored in that case).</p>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<dl class="method">
|
|||
|
|
<dt id="queue.Queue.put_nowait">
|
|||
|
|
<code class="descclassname">Queue.</code><code class="descname">put_nowait</code><span class="sig-paren">(</span><em>item</em><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.put_nowait" title="Permalink to this definition">¶</a></dt>
|
|||
|
|
<dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">put(item,</span> <span class="pre">False)</span></code>.</p>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<dl class="method">
|
|||
|
|
<dt id="queue.Queue.get">
|
|||
|
|
<code class="descclassname">Queue.</code><code class="descname">get</code><span class="sig-paren">(</span><em>block=True</em>, <em>timeout=None</em><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.get" title="Permalink to this definition">¶</a></dt>
|
|||
|
|
<dd><p>Remove and return an item from the queue. If optional args <em>block</em> is true and
|
|||
|
|
<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.
|
|||
|
|
If <em>timeout</em> is a positive number, it blocks at most <em>timeout</em> seconds and
|
|||
|
|
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.
|
|||
|
|
Otherwise (<em>block</em> is false), return an item if one is immediately available,
|
|||
|
|
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>
|
|||
|
|
<p>Prior to 3.0 on POSIX systems, and for all versions on Windows, if
|
|||
|
|
<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
|
|||
|
|
an uninterruptible wait on an underlying lock. This means that no exceptions
|
|||
|
|
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>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<dl class="method">
|
|||
|
|
<dt id="queue.Queue.get_nowait">
|
|||
|
|
<code class="descclassname">Queue.</code><code class="descname">get_nowait</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.get_nowait" title="Permalink to this definition">¶</a></dt>
|
|||
|
|
<dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">get(False)</span></code>.</p>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<p>Two methods are offered to support tracking whether enqueued tasks have been
|
|||
|
|
fully processed by daemon consumer threads.</p>
|
|||
|
|
<dl class="method">
|
|||
|
|
<dt id="queue.Queue.task_done">
|
|||
|
|
<code class="descclassname">Queue.</code><code class="descname">task_done</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.task_done" title="Permalink to this definition">¶</a></dt>
|
|||
|
|
<dd><p>Indicate that a formerly enqueued task is complete. Used by queue consumer
|
|||
|
|
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
|
|||
|
|
<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>
|
|||
|
|
<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
|
|||
|
|
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
|
|||
|
|
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>
|
|||
|
|
<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
|
|||
|
|
the queue.</p>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<dl class="method">
|
|||
|
|
<dt id="queue.Queue.join">
|
|||
|
|
<code class="descclassname">Queue.</code><code class="descname">join</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.Queue.join" title="Permalink to this definition">¶</a></dt>
|
|||
|
|
<dd><p>Blocks until all items in the queue have been gotten and processed.</p>
|
|||
|
|
<p>The count of unfinished tasks goes up whenever an item is added to the queue.
|
|||
|
|
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
|
|||
|
|
indicate that the item was retrieved and all work on it is complete. When the
|
|||
|
|
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>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<p>Example of how to wait for enqueued tasks to be completed:</p>
|
|||
|
|
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">worker</span><span class="p">():</span>
|
|||
|
|
<span class="k">while</span> <span class="kc">True</span><span class="p">:</span>
|
|||
|
|
<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>
|
|||
|
|
<span class="k">if</span> <span class="n">item</span> <span class="ow">is</span> <span class="kc">None</span><span class="p">:</span>
|
|||
|
|
<span class="k">break</span>
|
|||
|
|
<span class="n">do_work</span><span class="p">(</span><span class="n">item</span><span class="p">)</span>
|
|||
|
|
<span class="n">q</span><span class="o">.</span><span class="n">task_done</span><span class="p">()</span>
|
|||
|
|
|
|||
|
|
<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>
|
|||
|
|
<span class="n">threads</span> <span class="o">=</span> <span class="p">[]</span>
|
|||
|
|
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">num_worker_threads</span><span class="p">):</span>
|
|||
|
|
<span class="n">t</span> <span class="o">=</span> <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">t</span><span class="o">.</span><span class="n">start</span><span class="p">()</span>
|
|||
|
|
<span class="n">threads</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">t</span><span class="p">)</span>
|
|||
|
|
|
|||
|
|
<span class="k">for</span> <span class="n">item</span> <span class="ow">in</span> <span class="n">source</span><span class="p">():</span>
|
|||
|
|
<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>
|
|||
|
|
|
|||
|
|
<span class="c1"># block until all tasks are done</span>
|
|||
|
|
<span class="n">q</span><span class="o">.</span><span class="n">join</span><span class="p">()</span>
|
|||
|
|
|
|||
|
|
<span class="c1"># stop workers</span>
|
|||
|
|
<span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">num_worker_threads</span><span class="p">):</span>
|
|||
|
|
<span class="n">q</span><span class="o">.</span><span class="n">put</span><span class="p">(</span><span class="kc">None</span><span class="p">)</span>
|
|||
|
|
<span class="k">for</span> <span class="n">t</span> <span class="ow">in</span> <span class="n">threads</span><span class="p">:</span>
|
|||
|
|
<span class="n">t</span><span class="o">.</span><span class="n">join</span><span class="p">()</span>
|
|||
|
|
</pre></div>
|
|||
|
|
</div>
|
|||
|
|
</div>
|
|||
|
|
<div class="section" id="simplequeue-objects">
|
|||
|
|
<h2>SimpleQueue Objects<a class="headerlink" href="#simplequeue-objects" title="Permalink to this headline">¶</a></h2>
|
|||
|
|
<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>
|
|||
|
|
<dl class="method">
|
|||
|
|
<dt id="queue.SimpleQueue.qsize">
|
|||
|
|
<code class="descclassname">SimpleQueue.</code><code class="descname">qsize</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.qsize" title="Permalink to this definition">¶</a></dt>
|
|||
|
|
<dd><p>Return the approximate size of the queue. Note, qsize() > 0 doesn’t
|
|||
|
|
guarantee that a subsequent get() will not block.</p>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<dl class="method">
|
|||
|
|
<dt id="queue.SimpleQueue.empty">
|
|||
|
|
<code class="descclassname">SimpleQueue.</code><code class="descname">empty</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.empty" title="Permalink to this definition">¶</a></dt>
|
|||
|
|
<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()
|
|||
|
|
returns <code class="docutils literal notranslate"><span class="pre">False</span></code> it doesn’t guarantee that a subsequent call to get()
|
|||
|
|
will not block.</p>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<dl class="method">
|
|||
|
|
<dt id="queue.SimpleQueue.put">
|
|||
|
|
<code class="descclassname">SimpleQueue.</code><code class="descname">put</code><span class="sig-paren">(</span><em>item</em>, <em>block=True</em>, <em>timeout=None</em><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.put" title="Permalink to this definition">¶</a></dt>
|
|||
|
|
<dd><p>Put <em>item</em> into the queue. The method never blocks and always succeeds
|
|||
|
|
(except for potential low-level errors such as failure to allocate memory).
|
|||
|
|
The optional args <em>block</em> and <em>timeout</em> are ignored and only provided
|
|||
|
|
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>
|
|||
|
|
<div class="impl-detail compound">
|
|||
|
|
<p><strong>CPython implementation detail:</strong> This method has a C implementation which is reentrant. That is, a
|
|||
|
|
<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>
|
|||
|
|
call in the same thread without deadlocking or corrupting internal
|
|||
|
|
state inside the queue. This makes it appropriate for use in
|
|||
|
|
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>
|
|||
|
|
</div>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<dl class="method">
|
|||
|
|
<dt id="queue.SimpleQueue.put_nowait">
|
|||
|
|
<code class="descclassname">SimpleQueue.</code><code class="descname">put_nowait</code><span class="sig-paren">(</span><em>item</em><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.put_nowait" title="Permalink to this definition">¶</a></dt>
|
|||
|
|
<dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">put(item)</span></code>, provided for compatibility with
|
|||
|
|
<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>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<dl class="method">
|
|||
|
|
<dt id="queue.SimpleQueue.get">
|
|||
|
|
<code class="descclassname">SimpleQueue.</code><code class="descname">get</code><span class="sig-paren">(</span><em>block=True</em>, <em>timeout=None</em><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.get" title="Permalink to this definition">¶</a></dt>
|
|||
|
|
<dd><p>Remove and return an item from the queue. If optional args <em>block</em> is true and
|
|||
|
|
<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.
|
|||
|
|
If <em>timeout</em> is a positive number, it blocks at most <em>timeout</em> seconds and
|
|||
|
|
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.
|
|||
|
|
Otherwise (<em>block</em> is false), return an item if one is immediately available,
|
|||
|
|
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>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<dl class="method">
|
|||
|
|
<dt id="queue.SimpleQueue.get_nowait">
|
|||
|
|
<code class="descclassname">SimpleQueue.</code><code class="descname">get_nowait</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#queue.SimpleQueue.get_nowait" title="Permalink to this definition">¶</a></dt>
|
|||
|
|
<dd><p>Equivalent to <code class="docutils literal notranslate"><span class="pre">get(False)</span></code>.</p>
|
|||
|
|
</dd></dl>
|
|||
|
|
|
|||
|
|
<div class="admonition seealso">
|
|||
|
|
<p class="admonition-title">See also</p>
|
|||
|
|
<dl class="simple">
|
|||
|
|
<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)
|
|||
|
|
context.</p>
|
|||
|
|
</dd>
|
|||
|
|
</dl>
|
|||
|
|
<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
|
|||
|
|
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
|
|||
|
|
<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.</p>
|
|||
|
|
</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">queue</span></code> — A synchronized queue class</a><ul>
|
|||
|
|
<li><a class="reference internal" href="#queue-objects">Queue Objects</a></li>
|
|||
|
|
<li><a class="reference internal" href="#simplequeue-objects">SimpleQueue Objects</a></li>
|
|||
|
|
</ul>
|
|||
|
|
</li>
|
|||
|
|
</ul>
|
|||
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|
|
|||
|
|
<h4>Previous topic</h4>
|
|||
|
|
<p class="topless"><a href="sched.html"
|
|||
|
|
title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">sched</span></code> — Event scheduler</a></p>
|
|||
|
|
<h4>Next topic</h4>
|
|||
|
|
<p class="topless"><a href="_thread.html"
|
|||
|
|
title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">_thread</span></code> — Low-level threading API</a></p>
|
|||
|
|
<div role="note" aria-label="source link">
|
|||
|
|
<h3>This Page</h3>
|
|||
|
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|
|||
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<li><a href="../bugs.html">Report a Bug</a></li>
|
|||
|
|
<li>
|
|||
|
|
<a href="https://github.com/python/cpython/blob/3.7/Doc/library/queue.rst"
|
|||
|
|
rel="nofollow">Show Source
|
|||
|
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|
|||
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|
|||
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|
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|
|||
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|
|||
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|
|||
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|
|||
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|
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