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margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li class="switchers"> <div class="language_switcher_placeholder"></div> <div class="version_switcher_placeholder"></div> </li> <li> </li> <li id="cpython-language-and-version"> <a href="../index.html">3.12.3 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="python.html" accesskey="U">Python Runtime Services</a> »</li> <li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate"><span class="pre">abc</span></code> — Abstract Base Classes</a></li> <li class="right"> <div class="inline-search" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" /> <input type="submit" value="Go" /> </form> </div> | </li> <li class="right"> <label class="theme-selector-label"> Theme <select class="theme-selector" oninput="activateTheme(this.value)"> <option value="auto" selected>Auto</option> <option value="light">Light</option> <option value="dark">Dark</option> </select> </label> |</li> </ul> </div> <div class="document"> <div class="documentwrapper"> <div class="bodywrapper"> <div class="body" role="main"> <section id="module-abc"> <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> — Abstract Base Classes<a class="headerlink" href="#module-abc" title="Link to this heading">¶</a></h1> <p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.12/Lib/abc.py">Lib/abc.py</a></p> <hr class="docutils" /> <p>This module provides the infrastructure for defining <a class="reference internal" href="../glossary.html#term-abstract-base-class"><span class="xref std std-term">abstract base classes</span></a> (ABCs) in Python, as outlined in <span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-3119/"><strong>PEP 3119</strong></a>; see the PEP for why this was added to Python. (See also <span class="target" id="index-1"></span><a class="pep reference external" href="https://peps.python.org/pep-3141/"><strong>PEP 3141</strong></a> and the <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> module regarding a type hierarchy for numbers based on ABCs.)</p> <p>The <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> module has some concrete classes that derive from ABCs; these can, of course, be further derived. In addition, the <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> submodule has some ABCs that can be used to test whether a class or instance provides a particular interface, for example, if it is <a class="reference internal" href="../glossary.html#term-hashable"><span class="xref std std-term">hashable</span></a> or if it is a <a class="reference internal" href="../glossary.html#term-mapping"><span class="xref std std-term">mapping</span></a>.</p> <p>This module provides the metaclass <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> for defining ABCs and a helper class <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> to alternatively define ABCs through inheritance:</p> <dl class="py class"> <dt class="sig sig-object py" id="abc.ABC"> <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">abc.</span></span><span class="sig-name descname"><span class="pre">ABC</span></span><a class="headerlink" href="#abc.ABC" title="Link to this definition">¶</a></dt> <dd><p>A helper class that has <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> as its metaclass. With this class, an abstract base class can be created by simply deriving from <code class="xref py py-class docutils literal notranslate"><span class="pre">ABC</span></code> avoiding sometimes confusing metaclass usage, for example:</p> <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> <span class="k">class</span> <span class="nc">MyABC</span><span class="p">(</span><span class="n">ABC</span><span class="p">):</span> <span class="k">pass</span> </pre></div> </div> <p>Note that the type of <code class="xref py py-class docutils literal notranslate"><span class="pre">ABC</span></code> is still <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>, therefore inheriting from <code class="xref py py-class docutils literal notranslate"><span class="pre">ABC</span></code> requires the usual precautions regarding metaclass usage, as multiple inheritance may lead to metaclass conflicts. One may also define an abstract base class by passing the metaclass keyword and using <code class="xref py py-class docutils literal notranslate"><span class="pre">ABCMeta</span></code> directly, for example:</p> <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> <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> <span class="k">pass</span> </pre></div> </div> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.4.</span></p> </div> </dd></dl> <dl class="py class"> <dt class="sig sig-object py" id="abc.ABCMeta"> <em class="property"><span class="pre">class</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">abc.</span></span><span class="sig-name descname"><span class="pre">ABCMeta</span></span><a class="headerlink" href="#abc.ABCMeta" title="Link to this definition">¶</a></dt> <dd><p>Metaclass for defining Abstract Base Classes (ABCs).</p> <p>Use this metaclass to create an ABC. An ABC can be subclassed directly, and then acts as a mix-in class. You can also register unrelated concrete classes (even built-in classes) and unrelated ABCs as “virtual subclasses” – these and their descendants will be considered subclasses of the registering ABC by the built-in <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> function, but the registering ABC won’t show up in their MRO (Method Resolution Order) nor will method implementations defined by the registering ABC be callable (not even via <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>). <a class="footnote-reference brackets" href="#id2" id="id1" role="doc-noteref"><span class="fn-bracket">[</span>1<span class="fn-bracket">]</span></a></p> <p>Classes created with a metaclass of <code class="xref py py-class docutils literal notranslate"><span class="pre">ABCMeta</span></code> have the following method:</p> <dl class="py method"> <dt class="sig sig-object py" id="abc.ABCMeta.register"> <span class="sig-name descname"><span class="pre">register</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">subclass</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#abc.ABCMeta.register" title="Link to this definition">¶</a></dt> <dd><p>Register <em>subclass</em> as a “virtual subclass” of this ABC. For example:</p> <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> <span class="k">class</span> <span class="nc">MyABC</span><span class="p">(</span><span class="n">ABC</span><span class="p">):</span> <span class="k">pass</span> <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> <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> <span class="k">assert</span> <span class="nb">isinstance</span><span class="p">((),</span> <span class="n">MyABC</span><span class="p">)</span> </pre></div> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.3: </span>Returns the registered subclass, to allow usage as a class decorator.</p> </div> <div class="versionchanged"> <p><span class="versionmodified changed">Changed in version 3.4: </span>To detect calls to <code class="xref py py-meth docutils literal notranslate"><span class="pre">register()</span></code>, you can use the <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> function.</p> </div> </dd></dl> <p>You can also override this method in an abstract base class:</p> <dl class="py method"> <dt class="sig sig-object py" id="abc.ABCMeta.__subclasshook__"> <span class="sig-name descname"><span class="pre">__subclasshook__</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">subclass</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#abc.ABCMeta.__subclasshook__" title="Link to this definition">¶</a></dt> <dd><p>(Must be defined as a class method.)</p> <p>Check whether <em>subclass</em> is considered a subclass of this ABC. This means that you can customize the behavior of <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> further without the need to call <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> on every class you want to consider a subclass of the ABC. (This class method is called from the <a class="reference internal" href="../reference/datamodel.html#class.__subclasscheck__" title="class.__subclasscheck__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__subclasscheck__()</span></code></a> method of the ABC.)</p> <p>This method should return <code class="docutils literal notranslate"><span class="pre">True</span></code>, <code class="docutils literal notranslate"><span class="pre">False</span></code> or <a class="reference internal" href="constants.html#NotImplemented" title="NotImplemented"><code class="xref py py-data docutils literal notranslate"><span class="pre">NotImplemented</span></code></a>. If it returns <code class="docutils literal notranslate"><span class="pre">True</span></code>, the <em>subclass</em> is considered a subclass of this ABC. If it returns <code class="docutils literal notranslate"><span class="pre">False</span></code>, the <em>subclass</em> is not considered a subclass of this ABC, even if it would normally be one. If it returns <code class="xref py py-data docutils literal notranslate"><span class="pre">NotImplemented</span></code>, the subclass check is continued with the usual mechanism.</p> </dd></dl> <p>For a demonstration of these concepts, look at this example ABC definition:</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> <span class="o">...</span> <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> <span class="k">class</span> <span class="nc">MyIterable</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="fm">__iter__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span> <span class="k">while</span> <span class="kc">False</span><span class="p">:</span> <span class="k">yield</span> <span class="kc">None</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="bp">self</span><span class="o">.</span><span class="fm">__iter__</span><span class="p">()</span> <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>The ABC <code class="docutils literal notranslate"><span class="pre">MyIterable</span></code> defines the standard iterable method, <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>, as an abstract method. The implementation given here can still be called from subclasses. The <code class="xref py py-meth docutils literal notranslate"><span class="pre">get_iterator()</span></code> method is also part of the <code class="docutils literal notranslate"><span class="pre">MyIterable</span></code> abstract base class, but it does not have to be overridden in non-abstract derived classes.</p> <p>The <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> class method defined here says that any class that has an <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> method in its <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> (or in that of one of its base classes, accessed via the <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> list) is considered a <code class="docutils literal notranslate"><span class="pre">MyIterable</span></code> too.</p> <p>Finally, the last line makes <code class="docutils literal notranslate"><span class="pre">Foo</span></code> a virtual subclass of <code class="docutils literal notranslate"><span class="pre">MyIterable</span></code>, even though it does not define an <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> method (it uses the old-style iterable protocol, defined in terms of <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> and <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>). Note that this will not make <code class="docutils literal notranslate"><span class="pre">get_iterator</span></code> available as a method of <code class="docutils literal notranslate"><span class="pre">Foo</span></code>, so it is provided separately.</p> </dd></dl> <p>The <code class="xref py py-mod docutils literal notranslate"><span class="pre">abc</span></code> module also provides the following decorator:</p> <dl class="py function"> <dt class="sig sig-object py" id="abc.abstractmethod"> <span class="sig-prename descclassname"><span class="pre">@</span></span><span class="sig-prename descclassname"><span class="pre">abc.</span></span><span class="sig-name descname"><span class="pre">abstractmethod</span></span><a class="headerlink" href="#abc.abstractmethod" title="Link to this definition">¶</a></dt> <dd><p>A decorator indicating abstract methods.</p> <p>Using this decorator requires that the class’s metaclass is <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> or is derived from it. A class that has a metaclass derived from <code class="xref py py-class docutils literal notranslate"><span class="pre">ABCMeta</span></code> cannot be instantiated unless all of its abstract methods and properties are overridden. The abstract methods can be called using any of the normal ‘super’ call mechanisms. <code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code> may be used to declare abstract methods for properties and descriptors.</p> <p>Dynamically adding abstract methods to a class, or attempting to modify the abstraction status of a method or class once it is created, are only supported using the <a class="reference internal" href="#abc.update_abstractmethods" title="abc.update_abstractmethods"><code class="xref py py-func docutils literal notranslate"><span class="pre">update_abstractmethods()</span></code></a> function. The <code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code> only affects subclasses derived using regular inheritance; “virtual subclasses” registered with the ABC’s <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> method are not affected.</p> <p>When <code class="xref py py-func docutils literal notranslate"><span class="pre">abstractmethod()</span></code> is applied in combination with other method descriptors, it should be applied as the innermost decorator, as shown in the following usage examples:</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="n">arg1</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="n">arg2</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="n">arg3</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>In order to correctly interoperate with the abstract base class machinery, the descriptor must identify itself as abstract using <code class="xref py py-attr docutils literal notranslate"><span class="pre">__isabstractmethod__</span></code>. In general, this attribute should be <code class="docutils literal notranslate"><span class="pre">True</span></code> if any of the methods used to compose the descriptor are abstract. For example, Python’s built-in <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> does the equivalent of:</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">Note</p> <p>Unlike Java abstract methods, these abstract methods may have an implementation. This implementation can be called via the <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> mechanism from the class that overrides it. This could be useful as an end-point for a super-call in a framework that uses cooperative multiple-inheritance.</p> </div> </dd></dl> <p>The <code class="xref py py-mod docutils literal notranslate"><span class="pre">abc</span></code> module also supports the following legacy decorators:</p> <dl class="py function"> <dt class="sig sig-object py" id="abc.abstractclassmethod"> <span class="sig-prename descclassname"><span class="pre">@</span></span><span class="sig-prename descclassname"><span class="pre">abc.</span></span><span class="sig-name descname"><span class="pre">abstractclassmethod</span></span><a class="headerlink" href="#abc.abstractclassmethod" title="Link to this definition">¶</a></dt> <dd><div class="versionadded"> <p><span class="versionmodified added">New in version 3.2.</span></p> </div> <div class="deprecated"> <p><span class="versionmodified deprecated">Deprecated since version 3.3: </span>It is now possible to use <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> with <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>, making this decorator redundant.</p> </div> <p>A subclass of the built-in <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>, indicating an abstract classmethod. Otherwise it is similar to <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>This special case is deprecated, as the <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> decorator is now correctly identified as abstract when applied to an abstract method:</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="n">arg</span><span class="p">):</span> <span class="o">...</span> </pre></div> </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="abc.abstractstaticmethod"> <span class="sig-prename descclassname"><span class="pre">@</span></span><span class="sig-prename descclassname"><span class="pre">abc.</span></span><span class="sig-name descname"><span class="pre">abstractstaticmethod</span></span><a class="headerlink" href="#abc.abstractstaticmethod" title="Link to this definition">¶</a></dt> <dd><div class="versionadded"> <p><span class="versionmodified added">New in version 3.2.</span></p> </div> <div class="deprecated"> <p><span class="versionmodified deprecated">Deprecated since version 3.3: </span>It is now possible to use <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> with <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>, making this decorator redundant.</p> </div> <p>A subclass of the built-in <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>, indicating an abstract staticmethod. Otherwise it is similar to <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>This special case is deprecated, as the <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> decorator is now correctly identified as abstract when applied to an abstract method:</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="n">arg</span><span class="p">):</span> <span class="o">...</span> </pre></div> </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="abc.abstractproperty"> <span class="sig-prename descclassname"><span class="pre">@</span></span><span class="sig-prename descclassname"><span class="pre">abc.</span></span><span class="sig-name descname"><span class="pre">abstractproperty</span></span><a class="headerlink" href="#abc.abstractproperty" title="Link to this definition">¶</a></dt> <dd><div class="deprecated"> <p><span class="versionmodified deprecated">Deprecated since version 3.3: </span>It is now possible to use <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>, <a class="reference internal" href="functions.html#property.getter" title="property.getter"><code class="xref py py-meth docutils literal notranslate"><span class="pre">property.getter()</span></code></a>, <a class="reference internal" href="functions.html#property.setter" title="property.setter"><code class="xref py py-meth docutils literal notranslate"><span class="pre">property.setter()</span></code></a> and <a class="reference internal" href="functions.html#property.deleter" title="property.deleter"><code class="xref py py-meth docutils literal notranslate"><span class="pre">property.deleter()</span></code></a> with <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>, making this decorator redundant.</p> </div> <p>A subclass of the built-in <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>, indicating an abstract property.</p> <p>This special case is deprecated, as the <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> decorator is now correctly identified as abstract when applied to an abstract method:</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>The above example defines a read-only property; you can also define a read-write abstract property by appropriately marking one or more of the underlying methods as abstract:</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>If only some components are abstract, only those components need to be updated to create a concrete property in a subclass:</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>The <code class="xref py py-mod docutils literal notranslate"><span class="pre">abc</span></code> module also provides the following functions:</p> <dl class="py function"> <dt class="sig sig-object py" id="abc.get_cache_token"> <span class="sig-prename descclassname"><span class="pre">abc.</span></span><span class="sig-name descname"><span class="pre">get_cache_token</span></span><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#abc.get_cache_token" title="Link to this definition">¶</a></dt> <dd><p>Returns the current abstract base class cache token.</p> <p>The token is an opaque object (that supports equality testing) identifying the current version of the abstract base class cache for virtual subclasses. The token changes with every call to <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> on any ABC.</p> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.4.</span></p> </div> </dd></dl> <dl class="py function"> <dt class="sig sig-object py" id="abc.update_abstractmethods"> <span class="sig-prename descclassname"><span class="pre">abc.</span></span><span class="sig-name descname"><span class="pre">update_abstractmethods</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">cls</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#abc.update_abstractmethods" title="Link to this definition">¶</a></dt> <dd><p>A function to recalculate an abstract class’s abstraction status. This function should be called if a class’s abstract methods have been implemented or changed after it was created. Usually, this function should be called from within a class decorator.</p> <p>Returns <em>cls</em>, to allow usage as a class decorator.</p> <p>If <em>cls</em> is not an instance of <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>, does nothing.</p> <div class="admonition note"> <p class="admonition-title">Note</p> <p>This function assumes that <em>cls</em>’s superclasses are already updated. It does not update any subclasses.</p> </div> <div class="versionadded"> <p><span class="versionmodified added">New in version 3.10.</span></p> </div> </dd></dl> <p class="rubric">Footnotes</p> <aside class="footnote-list brackets"> <aside class="footnote brackets" id="id2" role="doc-footnote"> <span class="label"><span class="fn-bracket">[</span><a role="doc-backlink" href="#id1">1</a><span class="fn-bracket">]</span></span> <p>C++ programmers should note that Python’s virtual base class concept is not the same as C++’s.</p> </aside> </aside> </section> <div class="clearer"></div> </div> </div> </div> <div class="sphinxsidebar" role="navigation" aria-label="main navigation"> <div class="sphinxsidebarwrapper"> <div> <h4>Previous topic</h4> <p class="topless"><a href="contextlib.html" title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">contextlib</span></code> — Utilities for <code class="xref std std-keyword docutils literal notranslate"><span class="pre">with</span></code>-statement contexts</a></p> </div> <div> <h4>Next topic</h4> <p class="topless"><a href="atexit.html" title="next chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">atexit</span></code> — Exit handlers</a></p> </div> <div role="note" aria-label="source link"> <h3>This Page</h3> <ul class="this-page-menu"> <li><a href="../bugs.html">Report a Bug</a></li> <li> <a href="https://github.com/python/cpython/blob/main/Doc/library/abc.rst" rel="nofollow">Show Source </a> </li> </ul> </div> </div> <div id="sidebarbutton" title="Collapse sidebar"> <span>«</span> </div> </div> <div class="clearer"></div> </div> <div class="related" role="navigation" aria-label="related navigation"> <h3>Navigation</h3> <ul> <li class="right" style="margin-right: 10px"> <a href="../genindex.html" title="General Index" >index</a></li> <li class="right" > <a href="../py-modindex.html" title="Python Module Index" >modules</a> |</li> <li class="right" > <a href="atexit.html" title="atexit — Exit handlers" >next</a> |</li> <li class="right" > <a href="contextlib.html" title="contextlib — Utilities for with-statement contexts" >previous</a> |</li> <li><img src="../_static/py.svg" alt="Python logo" style="vertical-align: middle; margin-top: -1px"/></li> <li><a href="https://www.python.org/">Python</a> »</li> <li class="switchers"> <div class="language_switcher_placeholder"></div> <div class="version_switcher_placeholder"></div> </li> <li> </li> <li id="cpython-language-and-version"> <a href="../index.html">3.12.3 Documentation</a> » </li> <li class="nav-item nav-item-1"><a href="index.html" >The Python Standard Library</a> »</li> <li class="nav-item nav-item-2"><a href="python.html" >Python Runtime Services</a> »</li> <li class="nav-item nav-item-this"><a href=""><code class="xref py py-mod docutils literal notranslate"><span class="pre">abc</span></code> — Abstract Base Classes</a></li> <li class="right"> <div class="inline-search" role="search"> <form class="inline-search" action="../search.html" method="get"> <input placeholder="Quick search" aria-label="Quick search" type="search" name="q" id="search-box" /> <input type="submit" value="Go" /> </form> </div> | </li> <li class="right"> <label class="theme-selector-label"> Theme <select class="theme-selector" oninput="activateTheme(this.value)"> <option value="auto" selected>Auto</option> <option value="light">Light</option> <option value="dark">Dark</option> </select> </label> |</li> </ul> </div> <div class="footer"> © <a href="../copyright.html"> Copyright </a> 2001-2024, Python Software Foundation. <br /> This page is licensed under the Python Software Foundation License Version 2. <br /> Examples, recipes, and other code in the documentation are additionally licensed under the Zero Clause BSD License. <br /> See <a href="/license.html">History and License</a> for more information.<br /> <br /> The Python Software Foundation is a non-profit corporation. <a href="https://www.python.org/psf/donations/">Please donate.</a> <br /> <br /> Last updated on Apr 09, 2024 (13:47 UTC). <a href="/bugs.html">Found a bug</a>? <br /> Created using <a href="https://www.sphinx-doc.org/">Sphinx</a> 7.2.6. </div> </body> </html>