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<section id="reference-counting">
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<span id="countingrefs"></span><h1>引用计数<a class="headerlink" href="#reference-counting" title="永久链接至标题">¶</a></h1>
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<p>本节介绍的宏被用于管理 Python 对象的引用计数。</p>
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<dl class="function">
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<dt id="c.Py_INCREF">
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void <code class="sig-name descname">Py_INCREF</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_INCREF" title="永久链接至目标">¶</a></dt>
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<dd><p>增加对象 <em>o</em> 的引用计数。 对象必须不为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>；如果你不确定它不为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>，可使用 <a class="reference internal" href="#c.Py_XINCREF" title="Py_XINCREF"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_XINCREF()</span></code></a>。</p>
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</dd></dl>
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<dl class="function">
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<dt id="c.Py_XINCREF">
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void <code class="sig-name descname">Py_XINCREF</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_XINCREF" title="永久链接至目标">¶</a></dt>
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<dd><p>增加对象 <em>o</em> 的引用计数。 对象可以为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>，在此情况下该宏不产生任何效果。</p>
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</dd></dl>
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<dl class="function">
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<dt id="c.Py_DECREF">
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void <code class="sig-name descname">Py_DECREF</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_DECREF" title="永久链接至目标">¶</a></dt>
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<dd><p>减少对象 <em>o</em> 的引用计数。 对象必须不为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>；如果你不确定它不为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>，可使用 <a class="reference internal" href="#c.Py_XDECREF" title="Py_XDECREF"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_XDECREF()</span></code></a>。 如果引用计数降为零，将发起调用对象所属类型的释放函数 (它必须不为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>)。</p>
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<div class="admonition warning">
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<p class="admonition-title">警告</p>
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<p>释放函数可导致任意 Python 代码被发起调用（例如当一个带有 <a class="reference internal" href="../reference/datamodel.html#object.__del__" title="object.__del__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__del__()</span></code></a> 方法的类实例被释放时就是如此）。 虽然此类代码中的异常不会被传播，但被执行的代码能够自由访问所有 Python 全局变量。 这意味着任何可通过全局变量获取的对象在 <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_DECREF()</span></code></a> 被发起调用之前都应当处于完好状态。 例如，从一个列表中删除对象的代码应当将被删除对象的引用拷贝到一个临时变量中，更新列表数据结构，然后再为临时变量调用 <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_DECREF()</span></code></a>。</p>
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</div>
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</dd></dl>
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<dl class="function">
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<dt id="c.Py_XDECREF">
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void <code class="sig-name descname">Py_XDECREF</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_XDECREF" title="永久链接至目标">¶</a></dt>
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<dd><p>减少对象 <em>o</em> 的引用计数。 对象可以为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>，在此情况下该宏不产生任何效果；在其他情况下其效果与 <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_DECREF()</span></code></a> 相同，并会应用同样的警告。</p>
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</dd></dl>
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<dl class="function">
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<dt id="c.Py_CLEAR">
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void <code class="sig-name descname">Py_CLEAR</code><span class="sig-paren">(</span><a class="reference internal" href="structures.html#c.PyObject" title="PyObject">PyObject</a><em> *o</em><span class="sig-paren">)</span><a class="headerlink" href="#c.Py_CLEAR" title="永久链接至目标">¶</a></dt>
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<dd><p>减少对象 <em>o</em> 的引用计数。 对象可以为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>，在此情况下该宏不产生任何效果；在其他情况下其效果与 <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_DECREF()</span></code></a> 相同，区别在于其参数也会被设为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>。 针对 <a class="reference internal" href="#c.Py_DECREF" title="Py_DECREF"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_DECREF()</span></code></a> 的警告不适用于所传递的对象，因为该宏会细心地使用一个临时变量并在减少其引用计数之前将参数设为 <code class="docutils literal notranslate"><span class="pre">NULL</span></code>。</p>
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<p>每当要减少在垃圾回收期间可能会被遍历的对象的引用计数时，使用该宏是一个好主意。</p>
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</dd></dl>
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<p>以下函数适用于 Python 的运行时动态嵌入: <code class="docutils literal notranslate"><span class="pre">Py_IncRef(PyObject</span> <span class="pre">*o)</span></code>, <code class="docutils literal notranslate"><span class="pre">Py_DecRef(PyObject</span> <span class="pre">*o)</span></code>。 它们分别只是 <a class="reference internal" href="#c.Py_XINCREF" title="Py_XINCREF"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_XINCREF()</span></code></a> 和 <a class="reference internal" href="#c.Py_XDECREF" title="Py_XDECREF"><code class="xref c c-func docutils literal notranslate"><span class="pre">Py_XDECREF()</span></code></a> 的简单导出函数版本。</p>
|
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<p>以下函数或宏仅可在解释器核心内部使用: <code class="xref c c-func docutils literal notranslate"><span class="pre">_Py_Dealloc()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">_Py_ForgetReference()</span></code>, <code class="xref c c-func docutils literal notranslate"><span class="pre">_Py_NewReference()</span></code> 以及全局变量 <code class="xref c c-data docutils literal notranslate"><span class="pre">_Py_RefTotal</span></code>。</p>
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