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<h1 id="python-对象初探">Python 对象初探</h1>
<p>在Python的世界一切皆对象，不论是整数，还是字符串，甚至连类型、函数等都是一种对象。</p>
<h2 id="对象的分类">对象的分类</h2>
<p>以下是Python对象的大致的一个分类</p>
<ul>
<li>Fundamental 对象: 类型对象</li>
<li>Numeric 对象: 数值对象</li>
<li>Sequence 对象: 容纳其他对象的序列集合对象</li>
<li>Mapping 对象: 类似 C++中的 map 的关联对象</li>
<li>Internal 对象: Python 虚拟机在运行时内部使用的对象</li>
</ul>
<p><img src="object_category.jpg" alt="object category"></p>
<h2 id="对象机制的基石-pyobject">对象机制的基石 PyObject</h2>
<p>对于初学者来说这么多类型的对象怎么学？别着急，我们后续章节会解答。</p>
<p>在开始我们的学习之旅之前，我们要先认识一个结构体<strong>PyObject</strong>，可以说Python的对象机制就是基于<strong>PyObject</strong>拓展开来的，所以我们先看看<strong>PyObject</strong> 到底长什么样。</p>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Include/object.h#L106" target="_blank">Include/object.h</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Include/object.h</span>
<span class="token macro property">#<span class="token directive keyword">define</span> _PyObject_HEAD_EXTRA \
struct _object *_ob_next; \
struct _object *_ob_prev;</span>
<span class="token keyword">typedef</span> <span class="token keyword">struct</span> _object <span class="token punctuation">{</span>
_PyObject_HEAD_EXTRA <span class="token comment">// 双向链表 垃圾回收 需要用到</span>
Py_ssize_t ob_refcnt<span class="token punctuation">;</span> <span class="token comment">// 引用计数</span>
<span class="token keyword">struct</span> _typeobject <span class="token operator">*</span>ob_type<span class="token punctuation">;</span> <span class="token comment">// 指向类型对象的指针，决定了对象的类型</span>
<span class="token punctuation">}</span> PyObject<span class="token punctuation">;</span>
</code></pre>
<p>Python中的所有对象都拥有一些相同的内容，而这些内容就定义在<strong>PyObject</strong>中，</p>
<p><strong>PyObject</strong> 包含 一个用于垃圾回收的双向链表，一个引用计数变量 <code>ob_refcnt</code> 和 一个类型对象指针<code>ob_type</code></p>
<p><img src="PyObject.jpg" alt="PyObject"></p>
<h2 id="定长对象与变长对象">定长对象与变长对象</h2>
<p>Python对象除了前面提到的那种分类方法外，还可以分为定长对象和变长对象这两种形式。</p>
<p>变长对象都拥有一个相同的内容 <strong>PyVarObject</strong>，而 <strong>PyVarObject</strong>也是基于<strong>PyObject</strong>扩展的。</p>
<p>从代码中可以看出<strong>PyVarObject</strong>比<strong>PyObject</strong>多出了一个用于存储元素个数的变量<em>ob_size</em>。</p>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Include/object.h#L106" target="_blank">Include/object.h</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Include/object.h</span>
<span class="token keyword">typedef</span> <span class="token keyword">struct</span> _object <span class="token punctuation">{</span>
_PyObject_HEAD_EXTRA
Py_ssize_t ob_refcnt<span class="token punctuation">;</span>
<span class="token keyword">struct</span> _typeobject <span class="token operator">*</span>ob_type<span class="token punctuation">;</span>
<span class="token punctuation">}</span> PyObject<span class="token punctuation">;</span>
<span class="token keyword">typedef</span> <span class="token keyword">struct</span> <span class="token punctuation">{</span>
PyObject ob_base<span class="token punctuation">;</span>
Py_ssize_t ob_size<span class="token punctuation">;</span> <span class="token comment">/* Number of items in variable part */</span>
<span class="token punctuation">}</span> PyVarObject<span class="token punctuation">;</span>
</code></pre>
<p><img src="PyVarObject.jpg" alt="PyVarObject"></p>
<h2 id="类型对象">类型对象</h2>
<p>前面我们提到了<strong>PyObject</strong> 的 对象类型指针<code>struct _typeobject *ob_type</code>，它指向的类型对象就决定了一个对象是什么类型的。</p>
<p>这是一个非常重要的结构体，它不仅仅决定了一个对象的类型，还包含大量的<code>元信息</code>，
包括创建对象需要分配多少内存，对象都支持哪些操作等等。</p>
<p>接下来我们看一下<code>struct _typeobject</code>代码</p>
<p>在 <strong>PyTypeObject</strong> 的定义中包含许多信息，主要分类以下几类:</p>
<ul>
<li>类型名, tp_name, 主要用于 Python 内部调试用</li>
<li>创建该类型对象时分配的空间大小信息，即 <code>tp_basicsize</code> 和 <code>tp_itemsize</code></li>
<li>与该类型对象相关的操作信息(如 <code>tp_print</code> 这样的函数指针)</li>
<li>一些对象属性</li>
</ul>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Include/object.h#L346" target="_blank">Include/object.h</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Include/object.h</span>
<span class="token keyword">typedef</span> <span class="token keyword">struct</span> _typeobject <span class="token punctuation">{</span>
PyObject_VAR_HEAD
<span class="token keyword">const</span> <span class="token keyword">char</span> <span class="token operator">*</span>tp_name<span class="token punctuation">;</span> <span class="token comment">/* For printing, in format "<module>.<name>" */</span> <span class="token comment">// 类型名</span>
Py_ssize_t tp_basicsize<span class="token punctuation">,</span> tp_itemsize<span class="token punctuation">;</span> <span class="token comment">/* For allocation */</span>
<span class="token comment">// 创建该类型对象分配的内存空间大小</span>
<span class="token comment">// 一堆方法定义，函数和指针</span>
<span class="token comment">/* Methods to implement standard operations */</span>
destructor tp_dealloc<span class="token punctuation">;</span>
printfunc tp_print<span class="token punctuation">;</span>
getattrfunc tp_getattr<span class="token punctuation">;</span>
setattrfunc tp_setattr<span class="token punctuation">;</span>
PyAsyncMethods <span class="token operator">*</span>tp_as_async<span class="token punctuation">;</span> <span class="token comment">/* formerly known as tp_compare (Python 2)
or tp_reserved (Python 3) */</span>
reprfunc tp_repr<span class="token punctuation">;</span>
<span class="token comment">/* Method suites for standard classes */</span>
<span class="token comment">// 标准类方法集</span>
PyNumberMethods <span class="token operator">*</span>tp_as_number<span class="token punctuation">;</span> <span class="token comment">// 数值对象操作</span>
PySequenceMethods <span class="token operator">*</span>tp_as_sequence<span class="token punctuation">;</span> <span class="token comment">// 序列对象操作</span>
PyMappingMethods <span class="token operator">*</span>tp_as_mapping<span class="token punctuation">;</span> <span class="token comment">// 字典对象操作</span>
<span class="token comment">// 更多标准操作</span>
<span class="token comment">/* More standard operations (here for binary compatibility) */</span>
hashfunc tp_hash<span class="token punctuation">;</span>
ternaryfunc tp_call<span class="token punctuation">;</span>
reprfunc tp_str<span class="token punctuation">;</span>
getattrofunc tp_getattro<span class="token punctuation">;</span>
setattrofunc tp_setattro<span class="token punctuation">;</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span> PyTypeObject<span class="token punctuation">;</span>
</code></pre>
<h2 id="类型的类型">类型的类型</h2>
<p>在 <strong>PyTypeObjet</strong> 定义开始有一个宏<code>PyOject_VAR_HEAD</code>，查看源码可知 <strong>PyTypeObjet</strong> 是一个变长对象</p>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Include/object.h#L98" target="_blank">Include/object.h</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Include/object.h</span>
<span class="token macro property">#<span class="token directive keyword">define</span> PyObject_VAR_HEAD PyVarObject ob_base;</span>
</code></pre>
<p>对象的类型是由该对象指向的 类型对象 决定的，那么类型对象的类型是由谁决定的呢？
对于其他对象，可以通过与其关联的类型对象确定其类型，那么通过什么来确定一个对象是类型对象呢？
答案就是 <code>PyType_Type</code></p>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Objects/typeobject.c#L3540" target="_blank">Objects/typeobject.c</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Objects/typeobject.c</span>
PyTypeObject PyType_Type <span class="token operator">=</span> <span class="token punctuation">{</span>
<span class="token function">PyVarObject_HEAD_INIT</span><span class="token punctuation">(</span><span class="token operator">&</span>PyType_Type<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span>
<span class="token string">"type"</span><span class="token punctuation">,</span> <span class="token comment">/* tp_name */</span>
<span class="token keyword">sizeof</span><span class="token punctuation">(</span>PyHeapTypeObject<span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token comment">/* tp_basicsize */</span>
<span class="token keyword">sizeof</span><span class="token punctuation">(</span>PyMemberDef<span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token comment">/* tp_itemsize */</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre>
<p><code>PyType_Type</code> 在类型机制中至关重要，所有用户自定义 <code>class</code> 所
对应的 <code>PyTypeObject</code> 对象都是通过 <code>PyType_Type</code>创建的</p>
<p>接下来我们看 <code>PyLong_Type</code> 是怎么与 <code>PyType_Type</code> 建立联系的。
前面提到，在Python中，每一个对象都将自己的引用计数、类型信息保存在开始的部分中。
为了方便对这部分内存初始化，Python中提供了几个有用的宏:</p>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Include/object.h#L69" target="_blank">Include/object.h</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Include/object.h</span>
<span class="token macro property">#<span class="token directive keyword">ifdef</span> Py_TRACE_REFS</span>
<span class="token macro property">#<span class="token directive keyword">define</span> _PyObject_EXTRA_INIT 0, 0,</span>
<span class="token macro property">#<span class="token directive keyword">else</span></span>
<span class="token macro property">#<span class="token directive keyword">define</span> _PyObject_EXTRA_INIT</span>
<span class="token macro property">#<span class="token directive keyword">endif</span></span>
<span class="token macro property">#<span class="token directive keyword">define</span> PyObject_HEAD_INIT(type) \
{ _PyObject_EXTRA_INIT \
1, type },</span>
</code></pre>
<p>这些宏在各种内建类型对象的初始化中被大量使用。
以<code>PyLong_Type</code>为例，可以清晰的看到一般的类型对象和<code>PyType_Type</code>之间的关系</p>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Objects/longobject.c#L5379" target="_blank">Objects/longobject.c</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Objects/longobject.c</span>
PyTypeObject PyLong_Type <span class="token operator">=</span> <span class="token punctuation">{</span>
<span class="token function">PyVarObject_HEAD_INIT</span><span class="token punctuation">(</span><span class="token operator">&</span>PyType_Type<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span>
<span class="token string">"int"</span><span class="token punctuation">,</span> <span class="token comment">/* tp_name */</span>
<span class="token function">offsetof</span><span class="token punctuation">(</span>PyLongObject<span class="token punctuation">,</span> ob_digit<span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token comment">/* tp_basicsize */</span>
<span class="token keyword">sizeof</span><span class="token punctuation">(</span>digit<span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token comment">/* tp_itemsize */</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre>
<p>下图是对象运行时的图像表现</p>
<p><img src="object_runtime_relation.jpg" alt=""></p>
<h2 id="对象的创建">对象的创建</h2>
<p>Python创建对象有两种方式</p>
<h3 id="范型api-或称为-aol-abstract-object-layer">范型API 或称为 AOL (Abstract Object Layer)</h3>
<p>这类API通常形如<code>PyObject_XXX</code>这样的形式。可以应用在任何Python对象上，
如<code>PyObject_Print</code>。创建一个整数对象的方式</p>
<pre class="language-"><code class="lang-c">PyObject<span class="token operator">*</span> longobj <span class="token operator">=</span> <span class="token function">PyObject_New</span><span class="token punctuation">(</span>Pyobject<span class="token punctuation">,</span> <span class="token operator">&</span>PyLong_Type<span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<h3 id="与类型相关的api-或称为-col-concrete-object-layer">与类型相关的API 或称为 COL (Concrete Object Layer)</h3>
<p>这类API 通常只能作用于某一种类型的对象上，对于每一种内建对象
Python都提供了这样一组API。例如整数对象，我们可以利用如下的API创建</p>
<pre class="language-"><code class="lang-c">PyObject <span class="token operator">*</span>longObj <span class="token operator">=</span> <span class="token function">PyLong_FromLong</span><span class="token punctuation">(</span><span class="token number">10</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
</code></pre>
<h2 id="对象的行为">对象的行为</h2>
<p>在 <strong>PyTypeObject</strong> 中定义了大量的函数指针。这些函数指针可以视为类型对象中
所定义的操作，这些操作直接决定着一个对象在运行时所表现出的行为，比如 <strong>PyTypeObject</strong> 中的 <code>tp_hash</code> 指明了该类型对象如何生成其<code>hash</code>值。</p>
<p>在<strong>PyTypeObject</strong>的代码中，我们还可以看到非常重要的三组操作族</p>
<ul>
<li><code>PyNumberMethods *tp_as_number</code></li>
<li><code>PySequenceMethods *tp_as_sequence</code></li>
<li><code>PyMappingMethods *tp_as_mapping</code></li>
</ul>
<p><strong>PySequenceMethods</strong> 的代码如下</p>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Include/object.h#L240" target="_blank">Include/object.h</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Include/object.h</span>
<span class="token keyword">typedef</span> PyObject <span class="token operator">*</span> <span class="token punctuation">(</span><span class="token operator">*</span>binaryfunc<span class="token punctuation">)</span><span class="token punctuation">(</span>PyObject <span class="token operator">*</span><span class="token punctuation">,</span> PyObject <span class="token operator">*</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">typedef</span> <span class="token keyword">struct</span> <span class="token punctuation">{</span>
binaryfunc nb_matrix_multiply<span class="token punctuation">;</span>
binaryfunc nb_inplace_matrix_multiply<span class="token punctuation">;</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span> PyNumberMethods<span class="token punctuation">;</span>
</code></pre>
<p><strong>PyNumberMethods</strong> 定义了一个数值对象该支持的操作。一个数值对象如 整数对象，那么它的类型对象 <code>PyLong_Type</code>中<code>tp_as_number.nb_add</code>
就指定了它进行加法操作时的具体行为。</p>
<p>在以下代码中可以看出<code>PyLong_Type</code>中的<code>tp_as_number</code>项指向的是<code>long_as_number</code></p>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Objects/longobject.c#L5342" target="_blank">Objects/longobject.h</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Objects/longobject.c</span>
<span class="token keyword">static</span> PyNumberMethods long_as_number <span class="token operator">=</span> <span class="token punctuation">{</span>
<span class="token punctuation">(</span>binaryfunc<span class="token punctuation">)</span>long_add<span class="token punctuation">,</span> <span class="token comment">/*nb_add*/</span>
<span class="token punctuation">(</span>binaryfunc<span class="token punctuation">)</span>long_sub<span class="token punctuation">,</span> <span class="token comment">/*nb_subtract*/</span>
<span class="token punctuation">(</span>binaryfunc<span class="token punctuation">)</span>long_mul<span class="token punctuation">,</span> <span class="token comment">/*nb_multiply*/</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
PyTypeObject PyLong_Type <span class="token operator">=</span> <span class="token punctuation">{</span>
<span class="token function">PyVarObject_HEAD_INIT</span><span class="token punctuation">(</span><span class="token operator">&</span>PyType_Type<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span>
<span class="token string">"int"</span><span class="token punctuation">,</span> <span class="token comment">/* tp_name */</span>
<span class="token function">offsetof</span><span class="token punctuation">(</span>PyLongObject<span class="token punctuation">,</span> ob_digit<span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token comment">/* tp_basicsize */</span>
<span class="token keyword">sizeof</span><span class="token punctuation">(</span>digit<span class="token punctuation">)</span><span class="token punctuation">,</span> <span class="token comment">/* tp_itemsize */</span>
long_dealloc<span class="token punctuation">,</span> <span class="token comment">/* tp_dealloc */</span>
<span class="token number">0</span><span class="token punctuation">,</span> <span class="token comment">/* tp_print */</span>
<span class="token number">0</span><span class="token punctuation">,</span> <span class="token comment">/* tp_getattr */</span>
<span class="token number">0</span><span class="token punctuation">,</span> <span class="token comment">/* tp_setattr */</span>
<span class="token number">0</span><span class="token punctuation">,</span> <span class="token comment">/* tp_reserved */</span>
long_to_decimal_string<span class="token punctuation">,</span> <span class="token comment">/* tp_repr */</span>
<span class="token operator">&</span>long_as_number<span class="token punctuation">,</span> <span class="token comment">/* tp_as_number */</span>
<span class="token number">0</span><span class="token punctuation">,</span> <span class="token comment">/* tp_as_sequence */</span>
<span class="token number">0</span><span class="token punctuation">,</span> <span class="token comment">/* tp_as_mapping */</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre>
<p><code>PySequenceMethods *tp_as_sequence</code> 和 <code>PyMappingMethods *tp_as_mapping</code>的分析与<code>PyNumberMethods *tp_as_number</code> 相同，大家可以自行查阅源码</p>
<h2 id="对象的多态性">对象的多态性</h2>
<p>Python创建一个对象比如 <strong>PyLongObject</strong> 时，会分配内存进行初始化，然后
Python内部会用 <code>PyObject*</code> 变量来维护这个对象，其他对象也与此类似</p>
<p>所以在 Python 内部各个函数之间传递的都是一种范型指针 <code>PyObject*</code>
我们不知道这个指针所指的对象是什么类型，只能通过所指对象的 <code>ob_type</code> 域
动态进行判断，而Python正是通过 <code>ob_type</code> 实现了多态机制</p>
<p>考虑以下的 py_hash 函数</p>
<pre class="language-"><code class="lang-c">Py_hash_t
<span class="token function">calc_hash</span><span class="token punctuation">(</span>PyObject<span class="token operator">*</span> object<span class="token punctuation">)</span>
<span class="token punctuation">{</span>
Py_hash_t hash <span class="token operator">=</span> object<span class="token operator">-></span>ob_type<span class="token operator">-></span><span class="token function">tp_hash</span><span class="token punctuation">(</span>object<span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token keyword">return</span> hash<span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre>
<p>如果传递给 calc_hash 函数的指针是一个 <code>PyLongObject*</code>，那么它会调用 PyLongObject 对象对应的类型对象中定义的 hash操作<code>tp_hash</code>，<code>tp_hash</code>可以在**PyTypeObject中找到，
而具体赋值绑定我们可以在 <code>PyLong_Type</code> 初始化代码中看到绑定的是<code>long_hash</code>函数</p>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Objects/longobject.c#L5379" target="_blank">Objects/longobject.c</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Objects/longobject.c</span>
PyTypeObject PyLong_Type <span class="token operator">=</span> <span class="token punctuation">{</span>
<span class="token function">PyVarObject_HEAD_INIT</span><span class="token punctuation">(</span><span class="token operator">&</span>PyType_Type<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span>
<span class="token string">"int"</span><span class="token punctuation">,</span> <span class="token comment">/* tp_name */</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">(</span>hashfunc<span class="token punctuation">)</span>long_hash<span class="token punctuation">,</span> <span class="token comment">/* tp_hash */</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre>
<p>如果指针是一个 <code>PyUnicodeObject*</code>，那么就会调用 PyUnicodeObject 对象对应的类型对象中定义的输出操作，查看源码可以看到 实际绑定的是 <code>unicode_hash</code>函数</p>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Objects/unicodeobject.c#L15066" target="_blank">Objects/unicodeobject.c</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Objects/unicodeobject.c</span>
PyTypeObject PyUnicode_Type <span class="token operator">=</span> <span class="token punctuation">{</span>
<span class="token function">PyVarObject_HEAD_INIT</span><span class="token punctuation">(</span><span class="token operator">&</span>PyType_Type<span class="token punctuation">,</span> <span class="token number">0</span><span class="token punctuation">)</span>
<span class="token string">"str"</span><span class="token punctuation">,</span> <span class="token comment">/* tp_name */</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">(</span>hashfunc<span class="token punctuation">)</span> unicode_hash<span class="token punctuation">,</span> <span class="token comment">/* tp_hash*/</span>
<span class="token punctuation">.</span><span class="token punctuation">.</span><span class="token punctuation">.</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre>
<h2 id="引用计数">引用计数</h2>
<p>Python 通过引用计数来管理维护对象在内存中的存在与否</p>
<p>Python 中的每个东西都是一个对象， 都有<code>ob_refcnt</code> 变量，这个变量维护对象的引用计数，从而最终决定该对象的创建与销毁</p>
<p>在Python中，主要通过 <code>Py_INCREF(op)</code>与<code>Py_DECREF(op)</code> 这两个宏
来增加和减少对一个对象的引用计数。当一个对象的引用计数减少到0之后，
<code>Py_DECREF</code>将调用该对象的<code>tp_dealloc</code>来释放对象所占用的内存和系统资源；</p>
<p>但这并不意味着最终一定会调用 <code>free</code> 释放内存空间。因为频繁的申请、释放内存会大大降低Python的执行效率。因此Python中大量采用了内存对象池的技术，使得对象释放的空间归还给内存池而不是直接<code>free</code>，后续使用可先从对象池中获取</p>
<p><code>源文件：</code><a href="https://github.com/python/cpython/blob/v3.7.0/Include/object.h#L777" target="_blank">Include/object.h</a></p>
<pre class="language-"><code class="lang-c"><span class="token comment">// Include/object.h</span>
<span class="token macro property">#<span class="token directive keyword">define</span> _Py_NewReference(op) ( \
_Py_INC_TPALLOCS(op) _Py_COUNT_ALLOCS_COMMA \
_Py_INC_REFTOTAL _Py_REF_DEBUG_COMMA \
Py_REFCNT(op) = 1)</span>
<span class="token macro property">#<span class="token directive keyword">define</span> Py_INCREF(op) ( \
_Py_INC_REFTOTAL _Py_REF_DEBUG_COMMA \
((PyObject *)(op))->ob_refcnt++)</span>
<span class="token macro property">#<span class="token directive keyword">define</span> Py_DECREF(op) \
do { \
PyObject *_py_decref_tmp = (PyObject *)(op); \
if (_Py_DEC_REFTOTAL _Py_REF_DEBUG_COMMA \
--(_py_decref_tmp)->ob_refcnt != 0) \
_Py_CHECK_REFCNT(_py_decref_tmp) \
else \
_Py_Dealloc(_py_decref_tmp); \
} while (0)</span>
</code></pre>
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