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<section id="module-abc">
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<span id="abc-abstract-base-classes"></span><h1><a class="reference internal" href="#module-abc" title="abc: Abstract base classes according to :pep:`3119`."><code class="xref py py-mod docutils literal notranslate"><span class="pre">abc</span></code></a> --- 抽象基类<a class="headerlink" href="#module-abc" title="永久链接至标题">¶</a></h1>
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<p><strong>源代码：</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.8/Lib/abc.py">Lib/abc.py</a></p>
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<p>该模块提供了在 Python 中定义 <a class="reference internal" href="../glossary.html#term-abstract-base-class"><span class="xref std std-term">抽象基类</span></a> (ABC) 的组件，在 <span class="target" id="index-4"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3119"><strong>PEP 3119</strong></a> 中已有概述。查看 PEP 文档了解为什么需要在 Python 中增加这个模块。（也可查看 <span class="target" id="index-5"></span><a class="pep reference external" href="https://www.python.org/dev/peps/pep-3141"><strong>PEP 3141</strong></a> 以及 <a class="reference internal" href="numbers.html#module-numbers" title="numbers: Numeric abstract base classes (Complex, Real, Integral, etc.)."><code class="xref py py-mod docutils literal notranslate"><span class="pre">numbers</span></code></a> 模块了解基于 ABC 的数字类型继承关系。）</p>
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<p><a class="reference internal" href="collections.html#module-collections" title="collections: Container datatypes"><code class="xref py py-mod docutils literal notranslate"><span class="pre">collections</span></code></a> 模块中有一些派生自 ABC 的具体类；当然这些类还可以进一步被派生。此外，<a class="reference internal" href="collections.abc.html#module-collections.abc" title="collections.abc: Abstract base classes for containers"><code class="xref py py-mod docutils literal notranslate"><span class="pre">collections.abc</span></code></a> 子模块中有一些 ABC 可被用于测试一个类或实例是否提供特定的接口，例如它是否可哈希或它是否为映射等。</p>
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<p>该模块提供了一个元类 <a class="reference internal" href="#abc.ABCMeta" title="abc.ABCMeta"><code class="xref py py-class docutils literal notranslate"><span class="pre">ABCMeta</span></code></a>，可以用来定义抽象类，另外还提供一个工具类 <a class="reference internal" href="#abc.ABC" title="abc.ABC"><code class="xref py py-class docutils literal notranslate"><span class="pre">ABC</span></code></a>，可以用它以继承的方式定义抽象基类。</p>
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<dl class="class">
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<dt id="abc.ABC">
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<em class="property">class </em><code class="sig-prename descclassname">abc.</code><code class="sig-name descname">ABC</code><a class="headerlink" href="#abc.ABC" title="永久链接至目标">¶</a></dt>
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<dd><p>一个使用 <a class="reference internal" href="#abc.ABCMeta" title="abc.ABCMeta"><code class="xref py py-class docutils literal notranslate"><span class="pre">ABCMeta</span></code></a> 作为元类的工具类。抽象基类可以通过从 <a class="reference internal" href="#abc.ABC" title="abc.ABC"><code class="xref py py-class docutils literal notranslate"><span class="pre">ABC</span></code></a> 派生来简单地创建，这就避免了在某些情况下会令人混淆的元类用法，例如：</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">abc</span> <span class="kn">import</span> <span class="n">ABC</span>
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<span class="k">class</span> <span class="nc">MyABC</span><span class="p">(</span><span class="n">ABC</span><span class="p">):</span>
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<span class="k">pass</span>
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</pre></div>
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</div>
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<p>注意 <a class="reference internal" href="#abc.ABC" title="abc.ABC"><code class="xref py py-class docutils literal notranslate"><span class="pre">ABC</span></code></a> 的类型仍然是 <a class="reference internal" href="#abc.ABCMeta" title="abc.ABCMeta"><code class="xref py py-class docutils literal notranslate"><span class="pre">ABCMeta</span></code></a>，因此继承 <a class="reference internal" href="#abc.ABC" title="abc.ABC"><code class="xref py py-class docutils literal notranslate"><span class="pre">ABC</span></code></a> 仍然需要关注元类使用中的注意事项，比如可能会导致元类冲突的多重继承。当然你也可以直接使用 <a class="reference internal" href="#abc.ABCMeta" title="abc.ABCMeta"><code class="xref py py-class docutils literal notranslate"><span class="pre">ABCMeta</span></code></a> 作为元类来定义抽象基类，例如：</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">abc</span> <span class="kn">import</span> <span class="n">ABCMeta</span>
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<span class="k">class</span> <span class="nc">MyABC</span><span class="p">(</span><span class="n">metaclass</span><span class="o">=</span><span class="n">ABCMeta</span><span class="p">):</span>
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<span class="k">pass</span>
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</pre></div>
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</div>
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<div class="versionadded">
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<p><span class="versionmodified added">3.4 新版功能.</span></p>
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</div>
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</dd></dl>
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<dl class="class">
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<dt id="abc.ABCMeta">
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<em class="property">class </em><code class="sig-prename descclassname">abc.</code><code class="sig-name descname">ABCMeta</code><a class="headerlink" href="#abc.ABCMeta" title="永久链接至目标">¶</a></dt>
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<dd><p>用于定义抽象基类（ABC）的元类。</p>
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<p>使用该元类以创建抽象基类。抽象基类可以像 mix-in 类一样直接被子类继承。你也可以将不相关的具体类（包括内建类）和抽象基类注册为“抽象子类” —— 这些类以及它们的子类会被内建函数 <a class="reference internal" href="functions.html#issubclass" title="issubclass"><code class="xref py py-func docutils literal notranslate"><span class="pre">issubclass()</span></code></a> 识别为对应的抽象基类的子类，但是该抽象基类不会出现在其 MRO（Method Resolution Order，方法解析顺序）中，抽象基类中实现的方法也不可调用（即使通过 <a class="reference internal" href="functions.html#super" title="super"><code class="xref py py-func docutils literal notranslate"><span class="pre">super()</span></code></a> 调用也不行）。<a class="footnote-reference brackets" href="#id2" id="id1">1</a></p>
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<p>使用 <a class="reference internal" href="#abc.ABCMeta" title="abc.ABCMeta"><code class="xref py py-class docutils literal notranslate"><span class="pre">ABCMeta</span></code></a> 作为元类创建的类含有如下方法：</p>
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<dl class="method">
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<dt id="abc.ABCMeta.register">
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<code class="sig-name descname">register</code><span class="sig-paren">(</span><em class="sig-param">subclass</em><span class="sig-paren">)</span><a class="headerlink" href="#abc.ABCMeta.register" title="永久链接至目标">¶</a></dt>
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<dd><p>将 <em>subclass</em> 注册为该 ABC 的“虚拟子类”。 例如:</p>
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<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">abc</span> <span class="kn">import</span> <span class="n">ABC</span>
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<span class="k">class</span> <span class="nc">MyABC</span><span class="p">(</span><span class="n">ABC</span><span class="p">):</span>
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<span class="k">pass</span>
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<span class="n">MyABC</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="nb">tuple</span><span class="p">)</span>
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<span class="k">assert</span> <span class="nb">issubclass</span><span class="p">(</span><span class="nb">tuple</span><span class="p">,</span> <span class="n">MyABC</span><span class="p">)</span>
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<span class="k">assert</span> <span class="nb">isinstance</span><span class="p">((),</span> <span class="n">MyABC</span><span class="p">)</span>
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</pre></div>
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</div>
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<div class="versionchanged">
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<p><span class="versionmodified changed">在 3.3 版更改: </span>返回注册的子类，使其能够作为类装饰器。</p>
|
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</div>
|
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<div class="versionchanged">
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||
<p><span class="versionmodified changed">在 3.4 版更改: </span>你可以使用 <a class="reference internal" href="#abc.get_cache_token" title="abc.get_cache_token"><code class="xref py py-func docutils literal notranslate"><span class="pre">get_cache_token()</span></code></a> 函数来检测对 <a class="reference internal" href="#abc.ABCMeta.register" title="abc.ABCMeta.register"><code class="xref py py-meth docutils literal notranslate"><span class="pre">register()</span></code></a> 的调用。</p>
|
||
</div>
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</dd></dl>
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<p>你也可以在虚基类中重写这个方法。</p>
|
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<dl class="method">
|
||
<dt id="abc.ABCMeta.__subclasshook__">
|
||
<code class="sig-name descname">__subclasshook__</code><span class="sig-paren">(</span><em class="sig-param">subclass</em><span class="sig-paren">)</span><a class="headerlink" href="#abc.ABCMeta.__subclasshook__" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>（必须定义为类方法。）</p>
|
||
<p>检查 <em>subclass</em> 是否是该抽象基类的子类。也就是说对于那些你希望定义为该抽象基类的子类的类，你不用对每个类都调用 <a class="reference internal" href="#abc.ABCMeta.register" title="abc.ABCMeta.register"><code class="xref py py-meth docutils literal notranslate"><span class="pre">register()</span></code></a> 方法了，而是可以直接自定义 <code class="docutils literal notranslate"><span class="pre">issubclass</span></code> 的行为。（这个类方法是在抽象基类的 <code class="xref py py-meth docutils literal notranslate"><span class="pre">__subclasscheck__()</span></code> 方法中调用的。）</p>
|
||
<p>该方法必须返回 <code class="docutils literal notranslate"><span class="pre">True</span></code>, <code class="docutils literal notranslate"><span class="pre">False</span></code> 或是 <code class="docutils literal notranslate"><span class="pre">NotImplemented</span></code>。如果返回 <code class="docutils literal notranslate"><span class="pre">True</span></code>，<em>subclass</em> 就会被认为是这个抽象基类的子类。如果返回 <code class="docutils literal notranslate"><span class="pre">False</span></code>，无论正常情况是否应该认为是其子类，统一视为不是。如果返回 <code class="docutils literal notranslate"><span class="pre">NotImplemented</span></code>，子类检查会按照正常机制继续执行。</p>
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||
</dd></dl>
|
||
|
||
<p>为了对这些概念做一演示，请看以下定义 ABC 的示例：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Foo</span><span class="p">:</span>
|
||
<span class="k">def</span> <span class="fm">__getitem__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">index</span><span class="p">):</span>
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||
<span class="o">...</span>
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||
<span class="k">def</span> <span class="fm">__len__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
<span class="k">def</span> <span class="nf">get_iterator</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
|
||
<span class="k">return</span> <span class="nb">iter</span><span class="p">(</span><span class="bp">self</span><span class="p">)</span>
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||
|
||
<span class="k">class</span> <span class="nc">MyIterable</span><span class="p">(</span><span class="n">ABC</span><span class="p">):</span>
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|
||
<span class="nd">@abstractmethod</span>
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||
<span class="k">def</span> <span class="fm">__iter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
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||
<span class="k">while</span> <span class="kc">False</span><span class="p">:</span>
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||
<span class="k">yield</span> <span class="kc">None</span>
|
||
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||
<span class="k">def</span> <span class="nf">get_iterator</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
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<span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="fm">__iter__</span><span class="p">()</span>
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<span class="nd">@classmethod</span>
|
||
<span class="k">def</span> <span class="nf">__subclasshook__</span><span class="p">(</span><span class="bp">cls</span><span class="p">,</span> <span class="n">C</span><span class="p">):</span>
|
||
<span class="k">if</span> <span class="bp">cls</span> <span class="ow">is</span> <span class="n">MyIterable</span><span class="p">:</span>
|
||
<span class="k">if</span> <span class="nb">any</span><span class="p">(</span><span class="s2">"__iter__"</span> <span class="ow">in</span> <span class="n">B</span><span class="o">.</span><span class="vm">__dict__</span> <span class="k">for</span> <span class="n">B</span> <span class="ow">in</span> <span class="n">C</span><span class="o">.</span><span class="vm">__mro__</span><span class="p">):</span>
|
||
<span class="k">return</span> <span class="kc">True</span>
|
||
<span class="k">return</span> <span class="bp">NotImplemented</span>
|
||
|
||
<span class="n">MyIterable</span><span class="o">.</span><span class="n">register</span><span class="p">(</span><span class="n">Foo</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>ABC <code class="docutils literal notranslate"><span class="pre">MyIterable</span></code> 定义了标准的迭代方法 <a class="reference internal" href="stdtypes.html#iterator.__iter__" title="iterator.__iter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__iter__()</span></code></a> 作为一个抽象方法。这里给出的实现仍可在子类中被调用。<code class="xref py py-meth docutils literal notranslate"><span class="pre">get_iterator()</span></code> 方法也是 <code class="docutils literal notranslate"><span class="pre">MyIterable</span></code> 抽象基类的一部分，但它并非必须被非抽象派生类所重载。</p>
|
||
<p>这里定义的 <a class="reference internal" href="#abc.ABCMeta.__subclasshook__" title="abc.ABCMeta.__subclasshook__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__subclasshook__()</span></code></a> 类方法指明了任何在其 <a class="reference internal" href="stdtypes.html#object.__dict__" title="object.__dict__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__dict__</span></code></a> (或在其通过 <a class="reference internal" href="stdtypes.html#class.__mro__" title="class.__mro__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__mro__</span></code></a> 列表访问的基类) 中具有 <a class="reference internal" href="stdtypes.html#iterator.__iter__" title="iterator.__iter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__iter__()</span></code></a> 方法的类也都会被视为 <code class="docutils literal notranslate"><span class="pre">MyIterable</span></code>。</p>
|
||
<p>最后，末尾行使得 <code class="docutils literal notranslate"><span class="pre">Foo</span></code> 成为 <code class="docutils literal notranslate"><span class="pre">MyIterable</span></code> 的一个虚子类，即便它并没有定义 <a class="reference internal" href="stdtypes.html#iterator.__iter__" title="iterator.__iter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__iter__()</span></code></a> 方法（它使用了以 <a class="reference internal" href="../reference/datamodel.html#object.__len__" title="object.__len__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__len__()</span></code></a> 和 <a class="reference internal" href="../reference/datamodel.html#object.__getitem__" title="object.__getitem__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getitem__()</span></code></a> 术语定义的旧式可迭代对象协议）。注意这将不会使 <code class="docutils literal notranslate"><span class="pre">get_iterator</span></code> 成为对 <code class="docutils literal notranslate"><span class="pre">Foo</span></code> 来说可用的方法，所以也另外提供了一个它。</p>
|
||
</dd></dl>
|
||
|
||
<p>此外，<a class="reference internal" href="#module-abc" title="abc: Abstract base classes according to :pep:`3119`."><code class="xref py py-mod docutils literal notranslate"><span class="pre">abc</span></code></a> 模块还提供了这些装饰器：</p>
|
||
<dl class="function">
|
||
<dt id="abc.abstractmethod">
|
||
<code class="sig-prename descclassname">@</code><code class="sig-prename descclassname">abc.</code><code class="sig-name descname">abstractmethod</code><a class="headerlink" href="#abc.abstractmethod" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>用于声明抽象方法的装饰器。</p>
|
||
<p>使用此装饰器要求类的元类是 <a class="reference internal" href="#abc.ABCMeta" title="abc.ABCMeta"><code class="xref py py-class docutils literal notranslate"><span class="pre">ABCMeta</span></code></a> 或是从该类派生。一个具有派生自 <a class="reference internal" href="#abc.ABCMeta" title="abc.ABCMeta"><code class="xref py py-class docutils literal notranslate"><span class="pre">ABCMeta</span></code></a> 的元类的类不可以被实例化，除非它全部的抽象方法和特征属性均已被重载。抽象方法可通过任何普通的“super”调用机制来调用。 <a class="reference internal" href="#abc.abstractmethod" title="abc.abstractmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code></a> 可被用于声明特性属性和描述器的抽象方法。</p>
|
||
<p>不支持动态添加抽象方法到一个类，或试图在方法或类被创建后修改其抽象状态等操作。 <a class="reference internal" href="#abc.abstractmethod" title="abc.abstractmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code></a> 只会影响使用常规继承所派生的子类；通过 ABC 的 <code class="xref py py-meth docutils literal notranslate"><span class="pre">register()</span></code> 方法注册的“虚子类”不会受到影响。</p>
|
||
<p>当 <a class="reference internal" href="#abc.abstractmethod" title="abc.abstractmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code></a> 与其他方法描述符配合应用时，它应当被应用为最内层的装饰器，如以下用法示例所示:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="n">ABC</span><span class="p">):</span>
|
||
<span class="nd">@abstractmethod</span>
|
||
<span class="k">def</span> <span class="nf">my_abstract_method</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">...</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
<span class="nd">@classmethod</span>
|
||
<span class="nd">@abstractmethod</span>
|
||
<span class="k">def</span> <span class="nf">my_abstract_classmethod</span><span class="p">(</span><span class="bp">cls</span><span class="p">,</span> <span class="o">...</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
<span class="nd">@staticmethod</span>
|
||
<span class="nd">@abstractmethod</span>
|
||
<span class="k">def</span> <span class="nf">my_abstract_staticmethod</span><span class="p">(</span><span class="o">...</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
|
||
<span class="nd">@property</span>
|
||
<span class="nd">@abstractmethod</span>
|
||
<span class="k">def</span> <span class="nf">my_abstract_property</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
<span class="nd">@my_abstract_property</span><span class="o">.</span><span class="n">setter</span>
|
||
<span class="nd">@abstractmethod</span>
|
||
<span class="k">def</span> <span class="nf">my_abstract_property</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">val</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
|
||
<span class="nd">@abstractmethod</span>
|
||
<span class="k">def</span> <span class="nf">_get_x</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
<span class="nd">@abstractmethod</span>
|
||
<span class="k">def</span> <span class="nf">_set_x</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">val</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
<span class="n">x</span> <span class="o">=</span> <span class="nb">property</span><span class="p">(</span><span class="n">_get_x</span><span class="p">,</span> <span class="n">_set_x</span><span class="p">)</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>为了正确地与抽象基类机制互操作，描述器必须使用 <code class="xref py py-attr docutils literal notranslate"><span class="pre">__isabstractmethod__</span></code> 将自身标为抽象的。通常，如果组成描述器的任一方法是抽象的，那么此属性就应为 <code class="docutils literal notranslate"><span class="pre">True</span></code>。例如，Python 内置的 <a class="reference internal" href="functions.html#property" title="property"><code class="xref py py-class docutils literal notranslate"><span class="pre">property</span></code></a> 所做的就等价于：</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Descriptor</span><span class="p">:</span>
|
||
<span class="o">...</span>
|
||
<span class="nd">@property</span>
|
||
<span class="k">def</span> <span class="nf">__isabstractmethod__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
|
||
<span class="k">return</span> <span class="nb">any</span><span class="p">(</span><span class="nb">getattr</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="s1">'__isabstractmethod__'</span><span class="p">,</span> <span class="kc">False</span><span class="p">)</span> <span class="k">for</span>
|
||
<span class="n">f</span> <span class="ow">in</span> <span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">_fget</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">_fset</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">_fdel</span><span class="p">))</span>
|
||
</pre></div>
|
||
</div>
|
||
<div class="admonition note">
|
||
<p class="admonition-title">注解</p>
|
||
<p>不同于 Java 抽象方法，这些抽象方法可能具有一个实现。 这个实现可在重写它的类上通过 <a class="reference internal" href="functions.html#super" title="super"><code class="xref py py-func docutils literal notranslate"><span class="pre">super()</span></code></a> 机制来调用。 这在使用协作多重继承的框架中可以被用作 super 调用的一个终点。</p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<p><a class="reference internal" href="#module-abc" title="abc: Abstract base classes according to :pep:`3119`."><code class="xref py py-mod docutils literal notranslate"><span class="pre">abc</span></code></a> 模块还支持下列旧式装饰器:</p>
|
||
<dl class="function">
|
||
<dt id="abc.abstractclassmethod">
|
||
<code class="sig-prename descclassname">@</code><code class="sig-prename descclassname">abc.</code><code class="sig-name descname">abstractclassmethod</code><a class="headerlink" href="#abc.abstractclassmethod" title="永久链接至目标">¶</a></dt>
|
||
<dd><div class="versionadded">
|
||
<p><span class="versionmodified added">3.2 新版功能.</span></p>
|
||
</div>
|
||
<div class="deprecated">
|
||
<p><span class="versionmodified deprecated">3.3 版后已移除: </span>现在可以让 <a class="reference internal" href="functions.html#classmethod" title="classmethod"><code class="xref py py-class docutils literal notranslate"><span class="pre">classmethod</span></code></a> 配合 <a class="reference internal" href="#abc.abstractmethod" title="abc.abstractmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code></a> 使用，使得此装饰器变得冗余。</p>
|
||
</div>
|
||
<p>内置 <a class="reference internal" href="functions.html#classmethod" title="classmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">classmethod()</span></code></a> 的子类，指明一个抽象类方法。 在其他方面它都类似于 <a class="reference internal" href="#abc.abstractmethod" title="abc.abstractmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code></a>。</p>
|
||
<p>这个特例已被弃用，因为现在当 <a class="reference internal" href="functions.html#classmethod" title="classmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">classmethod()</span></code></a> 装饰器应用于抽象方法时它会被正确地标识为抽象的:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="n">ABC</span><span class="p">):</span>
|
||
<span class="nd">@classmethod</span>
|
||
<span class="nd">@abstractmethod</span>
|
||
<span class="k">def</span> <span class="nf">my_abstract_classmethod</span><span class="p">(</span><span class="bp">cls</span><span class="p">,</span> <span class="o">...</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
</pre></div>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="abc.abstractstaticmethod">
|
||
<code class="sig-prename descclassname">@</code><code class="sig-prename descclassname">abc.</code><code class="sig-name descname">abstractstaticmethod</code><a class="headerlink" href="#abc.abstractstaticmethod" title="永久链接至目标">¶</a></dt>
|
||
<dd><div class="versionadded">
|
||
<p><span class="versionmodified added">3.2 新版功能.</span></p>
|
||
</div>
|
||
<div class="deprecated">
|
||
<p><span class="versionmodified deprecated">3.3 版后已移除: </span>现在可以让 <a class="reference internal" href="functions.html#staticmethod" title="staticmethod"><code class="xref py py-class docutils literal notranslate"><span class="pre">staticmethod</span></code></a> 配合 <a class="reference internal" href="#abc.abstractmethod" title="abc.abstractmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code></a> 使用，使得此装饰器变得冗余。</p>
|
||
</div>
|
||
<p>内置 <a class="reference internal" href="functions.html#staticmethod" title="staticmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">staticmethod()</span></code></a> 的子类，指明一个抽象静态方法。 在其他方面它都类似于 <a class="reference internal" href="#abc.abstractmethod" title="abc.abstractmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code></a>。</p>
|
||
<p>这个特例已被弃用，因为现在当 <a class="reference internal" href="functions.html#staticmethod" title="staticmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">staticmethod()</span></code></a> 装饰器应用于抽象方法时它会被正确地标识为抽象的:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="n">ABC</span><span class="p">):</span>
|
||
<span class="nd">@staticmethod</span>
|
||
<span class="nd">@abstractmethod</span>
|
||
<span class="k">def</span> <span class="nf">my_abstract_staticmethod</span><span class="p">(</span><span class="o">...</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
</pre></div>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<dl class="function">
|
||
<dt id="abc.abstractproperty">
|
||
<code class="sig-prename descclassname">@</code><code class="sig-prename descclassname">abc.</code><code class="sig-name descname">abstractproperty</code><a class="headerlink" href="#abc.abstractproperty" title="永久链接至目标">¶</a></dt>
|
||
<dd><div class="deprecated">
|
||
<p><span class="versionmodified deprecated">3.3 版后已移除: </span>现在可以让 <a class="reference internal" href="functions.html#property" title="property"><code class="xref py py-class docutils literal notranslate"><span class="pre">property</span></code></a>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">property.getter()</span></code>, <code class="xref py py-meth docutils literal notranslate"><span class="pre">property.setter()</span></code> 和 <code class="xref py py-meth docutils literal notranslate"><span class="pre">property.deleter()</span></code> 配合 <a class="reference internal" href="#abc.abstractmethod" title="abc.abstractmethod"><code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code></a> 使用，使得此装饰器变得冗余。</p>
|
||
</div>
|
||
<p>内置 <a class="reference internal" href="functions.html#property" title="property"><code class="xref py py-func docutils literal notranslate"><span class="pre">property()</span></code></a> 的子类，指明一个抽象特性属性。</p>
|
||
<p>这个特例已被弃用，因为现在当 <a class="reference internal" href="functions.html#property" title="property"><code class="xref py py-func docutils literal notranslate"><span class="pre">property()</span></code></a> 装饰器应用于抽象方法时它会被正确地标识为抽象的:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="n">ABC</span><span class="p">):</span>
|
||
<span class="nd">@property</span>
|
||
<span class="nd">@abstractmethod</span>
|
||
<span class="k">def</span> <span class="nf">my_abstract_property</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>上面的例子定义了一个只读特征属性；你也可以通过适当地将一个或多个下层方法标记为抽象的来定义可读写的抽象特征属性:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">C</span><span class="p">(</span><span class="n">ABC</span><span class="p">):</span>
|
||
<span class="nd">@property</span>
|
||
<span class="k">def</span> <span class="nf">x</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
|
||
<span class="nd">@x</span><span class="o">.</span><span class="n">setter</span>
|
||
<span class="nd">@abstractmethod</span>
|
||
<span class="k">def</span> <span class="nf">x</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">val</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
</pre></div>
|
||
</div>
|
||
<p>如果只有某些组件是抽象的，则只需更新那些组件即可在子类中创建具体的特征属性:</p>
|
||
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">D</span><span class="p">(</span><span class="n">C</span><span class="p">):</span>
|
||
<span class="nd">@C</span><span class="o">.</span><span class="n">x</span><span class="o">.</span><span class="n">setter</span>
|
||
<span class="k">def</span> <span class="nf">x</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">val</span><span class="p">):</span>
|
||
<span class="o">...</span>
|
||
</pre></div>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<p><a class="reference internal" href="#module-abc" title="abc: Abstract base classes according to :pep:`3119`."><code class="xref py py-mod docutils literal notranslate"><span class="pre">abc</span></code></a> 模块还提供了这些函数：</p>
|
||
<dl class="function">
|
||
<dt id="abc.get_cache_token">
|
||
<code class="sig-prename descclassname">abc.</code><code class="sig-name descname">get_cache_token</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#abc.get_cache_token" title="永久链接至目标">¶</a></dt>
|
||
<dd><p>返回当前抽象基类的缓存令牌</p>
|
||
<p>此令牌是一个不透明对象（支持相等性测试），用于为虚子类标识抽象基类缓存的当前版本。 此令牌会在任何 ABC 上每次调用 <a class="reference internal" href="#abc.ABCMeta.register" title="abc.ABCMeta.register"><code class="xref py py-meth docutils literal notranslate"><span class="pre">ABCMeta.register()</span></code></a> 时发生更改。</p>
|
||
<div class="versionadded">
|
||
<p><span class="versionmodified added">3.4 新版功能.</span></p>
|
||
</div>
|
||
</dd></dl>
|
||
|
||
<p class="rubric">备注</p>
|
||
<dl class="footnote brackets">
|
||
<dt class="label" id="id2"><span class="brackets"><a class="fn-backref" href="#id1">1</a></span></dt>
|
||
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