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<div class="section" id="module-enum">
<span id="enum-support-for-enumerations"></span><h1><a class="reference internal" href="#module-enum" title="enum: Implementation of an enumeration class."><code class="xref py py-mod docutils literal notranslate"><span class="pre">enum</span></code></a> — Support for enumerations<a class="headerlink" href="#module-enum" title="Permalink to this headline">¶</a></h1>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.4.</span></p>
</div>
<p><strong>Source code:</strong> <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/enum.py">Lib/enum.py</a></p>
<hr class="docutils" />
<p>An enumeration is a set of symbolic names (members) bound to unique,
constant values. Within an enumeration, the members can be compared
by identity, and the enumeration itself can be iterated over.</p>
<div class="section" id="module-contents">
<h2>Module Contents<a class="headerlink" href="#module-contents" title="Permalink to this headline">¶</a></h2>
<p>This module defines four enumeration classes that can be used to define unique
sets of names and values: <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a>, <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntEnum</span></code></a>, <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate"><span class="pre">Flag</span></code></a>, and
<a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a>. It also defines one decorator, <a class="reference internal" href="#enum.unique" title="enum.unique"><code class="xref py py-func docutils literal notranslate"><span class="pre">unique()</span></code></a>, and one
helper, <a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate"><span class="pre">auto</span></code></a>.</p>
<dl class="class">
<dt id="enum.Enum">
<em class="property">class </em><code class="sig-prename descclassname">enum.</code><code class="sig-name descname">Enum</code><a class="headerlink" href="#enum.Enum" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for creating enumerated constants. See section
<a class="reference internal" href="#functional-api">Functional API</a> for an alternate construction syntax.</p>
</dd></dl>
<dl class="class">
<dt id="enum.IntEnum">
<em class="property">class </em><code class="sig-prename descclassname">enum.</code><code class="sig-name descname">IntEnum</code><a class="headerlink" href="#enum.IntEnum" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for creating enumerated constants that are also
subclasses of <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>.</p>
</dd></dl>
<dl class="class">
<dt id="enum.IntFlag">
<em class="property">class </em><code class="sig-prename descclassname">enum.</code><code class="sig-name descname">IntFlag</code><a class="headerlink" href="#enum.IntFlag" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for creating enumerated constants that can be combined using
the bitwise operators without losing their <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a> membership.
<a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a> members are also subclasses of <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>.</p>
</dd></dl>
<dl class="class">
<dt id="enum.Flag">
<em class="property">class </em><code class="sig-prename descclassname">enum.</code><code class="sig-name descname">Flag</code><a class="headerlink" href="#enum.Flag" title="Permalink to this definition">¶</a></dt>
<dd><p>Base class for creating enumerated constants that can be combined using
the bitwise operations without losing their <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate"><span class="pre">Flag</span></code></a> membership.</p>
</dd></dl>
<dl class="function">
<dt id="enum.unique">
<code class="sig-prename descclassname">enum.</code><code class="sig-name descname">unique</code><span class="sig-paren">(</span><span class="sig-paren">)</span><a class="headerlink" href="#enum.unique" title="Permalink to this definition">¶</a></dt>
<dd><p>Enum class decorator that ensures only one name is bound to any one value.</p>
</dd></dl>
<dl class="class">
<dt id="enum.auto">
<em class="property">class </em><code class="sig-prename descclassname">enum.</code><code class="sig-name descname">auto</code><a class="headerlink" href="#enum.auto" title="Permalink to this definition">¶</a></dt>
<dd><p>Instances are replaced with an appropriate value for Enum members. Initial value starts at 1.</p>
</dd></dl>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.6: </span><code class="docutils literal notranslate"><span class="pre">Flag</span></code>, <code class="docutils literal notranslate"><span class="pre">IntFlag</span></code>, <code class="docutils literal notranslate"><span class="pre">auto</span></code></p>
</div>
</div>
<div class="section" id="creating-an-enum">
<h2>Creating an Enum<a class="headerlink" href="#creating-an-enum" title="Permalink to this headline">¶</a></h2>
<p>Enumerations are created using the <a class="reference internal" href="../reference/compound_stmts.html#class"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">class</span></code></a> syntax, which makes them
easy to read and write. An alternative creation method is described in
<a class="reference internal" href="#functional-api">Functional API</a>. To define an enumeration, subclass <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> as
follows:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">enum</span> <span class="kn">import</span> <span class="n">Enum</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">...</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Enum member values</p>
<p>Member values can be anything: <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>, <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>, etc.. If
the exact value is unimportant you may use <a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate"><span class="pre">auto</span></code></a> instances and an
appropriate value will be chosen for you. Care must be taken if you mix
<a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate"><span class="pre">auto</span></code></a> with other values.</p>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Nomenclature</p>
<ul class="simple">
<li><p>The class <code class="xref py py-class docutils literal notranslate"><span class="pre">Color</span></code> is an <em>enumeration</em> (or <em>enum</em>)</p></li>
<li><p>The attributes <code class="xref py py-attr docutils literal notranslate"><span class="pre">Color.RED</span></code>, <code class="xref py py-attr docutils literal notranslate"><span class="pre">Color.GREEN</span></code>, etc., are
<em>enumeration members</em> (or <em>enum members</em>) and are functionally constants.</p></li>
<li><p>The enum members have <em>names</em> and <em>values</em> (the name of
<code class="xref py py-attr docutils literal notranslate"><span class="pre">Color.RED</span></code> is <code class="docutils literal notranslate"><span class="pre">RED</span></code>, the value of <code class="xref py py-attr docutils literal notranslate"><span class="pre">Color.BLUE</span></code> is
<code class="docutils literal notranslate"><span class="pre">3</span></code>, etc.)</p></li>
</ul>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Even though we use the <a class="reference internal" href="../reference/compound_stmts.html#class"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">class</span></code></a> syntax to create Enums, Enums
are not normal Python classes. See <a class="reference internal" href="#how-are-enums-different">How are Enums different?</a> for
more details.</p>
</div>
<p>Enumeration members have human readable string representations:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span><span class="p">)</span>
<span class="go">Color.RED</span>
</pre></div>
</div>
<p>…while their <code class="docutils literal notranslate"><span class="pre">repr</span></code> has more information:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="nb">repr</span><span class="p">(</span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span><span class="p">))</span>
<span class="go"><Color.RED: 1></span>
</pre></div>
</div>
<p>The <em>type</em> of an enumeration member is the enumeration it belongs to:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">type</span><span class="p">(</span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span><span class="p">)</span>
<span class="go"><enum 'Color'></span>
<span class="gp">>>> </span><span class="nb">isinstance</span><span class="p">(</span><span class="n">Color</span><span class="o">.</span><span class="n">GREEN</span><span class="p">,</span> <span class="n">Color</span><span class="p">)</span>
<span class="go">True</span>
<span class="go">>>></span>
</pre></div>
</div>
<p>Enum members also have a property that contains just their item name:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">print</span><span class="p">(</span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span><span class="o">.</span><span class="n">name</span><span class="p">)</span>
<span class="go">RED</span>
</pre></div>
</div>
<p>Enumerations support iteration, in definition order:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Shake</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">VANILLA</span> <span class="o">=</span> <span class="mi">7</span>
<span class="gp">... </span> <span class="n">CHOCOLATE</span> <span class="o">=</span> <span class="mi">4</span>
<span class="gp">... </span> <span class="n">COOKIES</span> <span class="o">=</span> <span class="mi">9</span>
<span class="gp">... </span> <span class="n">MINT</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="k">for</span> <span class="n">shake</span> <span class="ow">in</span> <span class="n">Shake</span><span class="p">:</span>
<span class="gp">... </span> <span class="nb">print</span><span class="p">(</span><span class="n">shake</span><span class="p">)</span>
<span class="gp">...</span>
<span class="go">Shake.VANILLA</span>
<span class="go">Shake.CHOCOLATE</span>
<span class="go">Shake.COOKIES</span>
<span class="go">Shake.MINT</span>
</pre></div>
</div>
<p>Enumeration members are hashable, so they can be used in dictionaries and sets:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">apples</span> <span class="o">=</span> <span class="p">{}</span>
<span class="gp">>>> </span><span class="n">apples</span><span class="p">[</span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'red delicious'</span>
<span class="gp">>>> </span><span class="n">apples</span><span class="p">[</span><span class="n">Color</span><span class="o">.</span><span class="n">GREEN</span><span class="p">]</span> <span class="o">=</span> <span class="s1">'granny smith'</span>
<span class="gp">>>> </span><span class="n">apples</span> <span class="o">==</span> <span class="p">{</span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span><span class="p">:</span> <span class="s1">'red delicious'</span><span class="p">,</span> <span class="n">Color</span><span class="o">.</span><span class="n">GREEN</span><span class="p">:</span> <span class="s1">'granny smith'</span><span class="p">}</span>
<span class="go">True</span>
</pre></div>
</div>
</div>
<div class="section" id="programmatic-access-to-enumeration-members-and-their-attributes">
<h2>Programmatic access to enumeration members and their attributes<a class="headerlink" href="#programmatic-access-to-enumeration-members-and-their-attributes" title="Permalink to this headline">¶</a></h2>
<p>Sometimes it’s useful to access members in enumerations programmatically (i.e.
situations where <code class="docutils literal notranslate"><span class="pre">Color.RED</span></code> won’t do because the exact color is not known
at program-writing time). <code class="docutils literal notranslate"><span class="pre">Enum</span></code> allows such access:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Color</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span>
<span class="go"><Color.RED: 1></span>
<span class="gp">>>> </span><span class="n">Color</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span>
<span class="go"><Color.BLUE: 3></span>
</pre></div>
</div>
<p>If you want to access enum members by <em>name</em>, use item access:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Color</span><span class="p">[</span><span class="s1">'RED'</span><span class="p">]</span>
<span class="go"><Color.RED: 1></span>
<span class="gp">>>> </span><span class="n">Color</span><span class="p">[</span><span class="s1">'GREEN'</span><span class="p">]</span>
<span class="go"><Color.GREEN: 2></span>
</pre></div>
</div>
<p>If you have an enum member and need its <code class="xref py py-attr docutils literal notranslate"><span class="pre">name</span></code> or <code class="xref py py-attr docutils literal notranslate"><span class="pre">value</span></code>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">member</span> <span class="o">=</span> <span class="n">Color</span><span class="o">.</span><span class="n">RED</span>
<span class="gp">>>> </span><span class="n">member</span><span class="o">.</span><span class="n">name</span>
<span class="go">'RED'</span>
<span class="gp">>>> </span><span class="n">member</span><span class="o">.</span><span class="n">value</span>
<span class="go">1</span>
</pre></div>
</div>
</div>
<div class="section" id="duplicating-enum-members-and-values">
<h2>Duplicating enum members and values<a class="headerlink" href="#duplicating-enum-members-and-values" title="Permalink to this headline">¶</a></h2>
<p>Having two enum members with the same name is invalid:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Shape</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">SQUARE</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">... </span> <span class="n">SQUARE</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">...</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">TypeError</span>: <span class="n">Attempted to reuse key: 'SQUARE'</span>
</pre></div>
</div>
<p>However, two enum members are allowed to have the same value. Given two members
A and B with the same value (and A defined first), B is an alias to A. By-value
lookup of the value of A and B will return A. By-name lookup of B will also
return A:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Shape</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">SQUARE</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">... </span> <span class="n">DIAMOND</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">CIRCLE</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">... </span> <span class="n">ALIAS_FOR_SQUARE</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Shape</span><span class="o">.</span><span class="n">SQUARE</span>
<span class="go"><Shape.SQUARE: 2></span>
<span class="gp">>>> </span><span class="n">Shape</span><span class="o">.</span><span class="n">ALIAS_FOR_SQUARE</span>
<span class="go"><Shape.SQUARE: 2></span>
<span class="gp">>>> </span><span class="n">Shape</span><span class="p">(</span><span class="mi">2</span><span class="p">)</span>
<span class="go"><Shape.SQUARE: 2></span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>Attempting to create a member with the same name as an already
defined attribute (another member, a method, etc.) or attempting to create
an attribute with the same name as a member is not allowed.</p>
</div>
</div>
<div class="section" id="ensuring-unique-enumeration-values">
<h2>Ensuring unique enumeration values<a class="headerlink" href="#ensuring-unique-enumeration-values" title="Permalink to this headline">¶</a></h2>
<p>By default, enumerations allow multiple names as aliases for the same value.
When this behavior isn’t desired, the following decorator can be used to
ensure each value is used only once in the enumeration:</p>
<dl class="function">
<dt>
<code class="sig-prename descclassname">@</code><code class="sig-prename descclassname">enum.</code><code class="sig-name descname">unique</code></dt>
<dd></dd></dl>
<p>A <a class="reference internal" href="../reference/compound_stmts.html#class"><code class="xref std std-keyword docutils literal notranslate"><span class="pre">class</span></code></a> decorator specifically for enumerations. It searches an
enumeration’s <code class="xref py py-attr docutils literal notranslate"><span class="pre">__members__</span></code> gathering any aliases it finds; if any are
found <a class="reference internal" href="exceptions.html#ValueError" title="ValueError"><code class="xref py py-exc docutils literal notranslate"><span class="pre">ValueError</span></code></a> is raised with the details:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">enum</span> <span class="kn">import</span> <span class="n">Enum</span><span class="p">,</span> <span class="n">unique</span>
<span class="gp">>>> </span><span class="nd">@unique</span>
<span class="gp">... </span><span class="k">class</span> <span class="nc">Mistake</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">ONE</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">TWO</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">... </span> <span class="n">THREE</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">... </span> <span class="n">FOUR</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">...</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">ValueError</span>: <span class="n">duplicate values found in <enum 'Mistake'>: FOUR -> THREE</span>
</pre></div>
</div>
</div>
<div class="section" id="using-automatic-values">
<h2>Using automatic values<a class="headerlink" href="#using-automatic-values" title="Permalink to this headline">¶</a></h2>
<p>If the exact value is unimportant you can use <a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate"><span class="pre">auto</span></code></a>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">enum</span> <span class="kn">import</span> <span class="n">Enum</span><span class="p">,</span> <span class="n">auto</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">Color</span><span class="p">)</span>
<span class="go">[<Color.RED: 1>, <Color.BLUE: 2>, <Color.GREEN: 3>]</span>
</pre></div>
</div>
<p>The values are chosen by <code class="xref py py-func docutils literal notranslate"><span class="pre">_generate_next_value_()</span></code>, which can be
overridden:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">AutoName</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">_generate_next_value_</span><span class="p">(</span><span class="n">name</span><span class="p">,</span> <span class="n">start</span><span class="p">,</span> <span class="n">count</span><span class="p">,</span> <span class="n">last_values</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">name</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Ordinal</span><span class="p">(</span><span class="n">AutoName</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">NORTH</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">SOUTH</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">EAST</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">WEST</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">Ordinal</span><span class="p">)</span>
<span class="go">[<Ordinal.NORTH: 'NORTH'>, <Ordinal.SOUTH: 'SOUTH'>, <Ordinal.EAST: 'EAST'>, <Ordinal.WEST: 'WEST'>]</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The goal of the default <code class="xref py py-meth docutils literal notranslate"><span class="pre">_generate_next_value_()</span></code> methods is to provide
the next <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a> in sequence with the last <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a> provided, but
the way it does this is an implementation detail and may change.</p>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <code class="xref py py-meth docutils literal notranslate"><span class="pre">_generate_next_value_()</span></code> method must be defined before any members.</p>
</div>
</div>
<div class="section" id="iteration">
<h2>Iteration<a class="headerlink" href="#iteration" title="Permalink to this headline">¶</a></h2>
<p>Iterating over the members of an enum does not provide the aliases:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">Shape</span><span class="p">)</span>
<span class="go">[<Shape.SQUARE: 2>, <Shape.DIAMOND: 1>, <Shape.CIRCLE: 3>]</span>
</pre></div>
</div>
<p>The special attribute <code class="docutils literal notranslate"><span class="pre">__members__</span></code> is an ordered dictionary mapping names
to members. It includes all names defined in the enumeration, including the
aliases:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">for</span> <span class="n">name</span><span class="p">,</span> <span class="n">member</span> <span class="ow">in</span> <span class="n">Shape</span><span class="o">.</span><span class="n">__members__</span><span class="o">.</span><span class="n">items</span><span class="p">():</span>
<span class="gp">... </span> <span class="n">name</span><span class="p">,</span> <span class="n">member</span>
<span class="gp">...</span>
<span class="go">('SQUARE', <Shape.SQUARE: 2>)</span>
<span class="go">('DIAMOND', <Shape.DIAMOND: 1>)</span>
<span class="go">('CIRCLE', <Shape.CIRCLE: 3>)</span>
<span class="go">('ALIAS_FOR_SQUARE', <Shape.SQUARE: 2>)</span>
</pre></div>
</div>
<p>The <code class="docutils literal notranslate"><span class="pre">__members__</span></code> attribute can be used for detailed programmatic access to
the enumeration members. For example, finding all the aliases:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="p">[</span><span class="n">name</span> <span class="k">for</span> <span class="n">name</span><span class="p">,</span> <span class="n">member</span> <span class="ow">in</span> <span class="n">Shape</span><span class="o">.</span><span class="n">__members__</span><span class="o">.</span><span class="n">items</span><span class="p">()</span> <span class="k">if</span> <span class="n">member</span><span class="o">.</span><span class="n">name</span> <span class="o">!=</span> <span class="n">name</span><span class="p">]</span>
<span class="go">['ALIAS_FOR_SQUARE']</span>
</pre></div>
</div>
</div>
<div class="section" id="comparisons">
<h2>Comparisons<a class="headerlink" href="#comparisons" title="Permalink to this headline">¶</a></h2>
<p>Enumeration members are compared by identity:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span> <span class="ow">is</span> <span class="n">Color</span><span class="o">.</span><span class="n">RED</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span> <span class="ow">is</span> <span class="n">Color</span><span class="o">.</span><span class="n">BLUE</span>
<span class="go">False</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span> <span class="ow">is</span> <span class="ow">not</span> <span class="n">Color</span><span class="o">.</span><span class="n">BLUE</span>
<span class="go">True</span>
</pre></div>
</div>
<p>Ordered comparisons between enumeration values are <em>not</em> supported. Enum
members are not integers (but see <a class="reference internal" href="#intenum">IntEnum</a> below):</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span> <span class="o"><</span> <span class="n">Color</span><span class="o">.</span><span class="n">BLUE</span>
<span class="gt">Traceback (most recent call last):</span>
File <span class="nb">"<stdin>"</span>, line <span class="m">1</span>, in <span class="n"><module></span>
<span class="gr">TypeError</span>: <span class="n">'<' not supported between instances of 'Color' and 'Color'</span>
</pre></div>
</div>
<p>Equality comparisons are defined though:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">BLUE</span> <span class="o">==</span> <span class="n">Color</span><span class="o">.</span><span class="n">RED</span>
<span class="go">False</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">BLUE</span> <span class="o">!=</span> <span class="n">Color</span><span class="o">.</span><span class="n">RED</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">BLUE</span> <span class="o">==</span> <span class="n">Color</span><span class="o">.</span><span class="n">BLUE</span>
<span class="go">True</span>
</pre></div>
</div>
<p>Comparisons against non-enumeration values will always compare not equal
(again, <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntEnum</span></code></a> was explicitly designed to behave differently, see
below):</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">BLUE</span> <span class="o">==</span> <span class="mi">2</span>
<span class="go">False</span>
</pre></div>
</div>
</div>
<div class="section" id="allowed-members-and-attributes-of-enumerations">
<h2>Allowed members and attributes of enumerations<a class="headerlink" href="#allowed-members-and-attributes-of-enumerations" title="Permalink to this headline">¶</a></h2>
<p>The examples above use integers for enumeration values. Using integers is
short and handy (and provided by default by the <a class="reference internal" href="#functional-api">Functional API</a>), but not
strictly enforced. In the vast majority of use-cases, one doesn’t care what
the actual value of an enumeration is. But if the value <em>is</em> important,
enumerations can have arbitrary values.</p>
<p>Enumerations are Python classes, and can have methods and special methods as
usual. If we have this enumeration:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Mood</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">FUNKY</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">HAPPY</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">describe</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="c1"># self is the member here</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">name</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">value</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="k">def</span> <span class="fm">__str__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="s1">'my custom str! </span><span class="si">{0}</span><span class="s1">'</span><span class="o">.</span><span class="n">format</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">value</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">... </span> <span class="nd">@classmethod</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">favorite_mood</span><span class="p">(</span><span class="bp">cls</span><span class="p">):</span>
<span class="gp">... </span> <span class="c1"># cls here is the enumeration</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">cls</span><span class="o">.</span><span class="n">HAPPY</span>
<span class="gp">...</span>
</pre></div>
</div>
<p>Then:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Mood</span><span class="o">.</span><span class="n">favorite_mood</span><span class="p">()</span>
<span class="go"><Mood.HAPPY: 3></span>
<span class="gp">>>> </span><span class="n">Mood</span><span class="o">.</span><span class="n">HAPPY</span><span class="o">.</span><span class="n">describe</span><span class="p">()</span>
<span class="go">('HAPPY', 3)</span>
<span class="gp">>>> </span><span class="nb">str</span><span class="p">(</span><span class="n">Mood</span><span class="o">.</span><span class="n">FUNKY</span><span class="p">)</span>
<span class="go">'my custom str! 1'</span>
</pre></div>
</div>
<p>The rules for what is allowed are as follows: names that start and end with
a single underscore are reserved by enum and cannot be used; all other
attributes defined within an enumeration will become members of this
enumeration, with the exception of special methods (<a class="reference internal" href="../reference/datamodel.html#object.__str__" title="object.__str__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__str__()</span></code></a>,
<a class="reference internal" href="../reference/datamodel.html#object.__add__" title="object.__add__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__add__()</span></code></a>, etc.), descriptors (methods are also descriptors), and
variable names listed in <code class="xref py py-attr docutils literal notranslate"><span class="pre">_ignore_</span></code>.</p>
<p>Note: if your enumeration defines <a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__new__()</span></code></a> and/or <a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__init__()</span></code></a> then
whatever value(s) were given to the enum member will be passed into those
methods. See <a class="reference internal" href="#planet">Planet</a> for an example.</p>
</div>
<div class="section" id="restricted-enum-subclassing">
<h2>Restricted Enum subclassing<a class="headerlink" href="#restricted-enum-subclassing" title="Permalink to this headline">¶</a></h2>
<p>A new <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> class must have one base Enum class, up to one concrete
data type, and as many <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate"><span class="pre">object</span></code></a>-based mixin classes as needed. The
order of these base classes is:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">EnumName</span><span class="p">([</span><span class="n">mix</span><span class="o">-</span><span class="ow">in</span><span class="p">,</span> <span class="o">...</span><span class="p">,]</span> <span class="p">[</span><span class="n">data</span><span class="o">-</span><span class="nb">type</span><span class="p">,]</span> <span class="n">base</span><span class="o">-</span><span class="n">enum</span><span class="p">):</span>
<span class="k">pass</span>
</pre></div>
</div>
<p>Also, subclassing an enumeration is allowed only if the enumeration does not define
any members. So this is forbidden:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">MoreColor</span><span class="p">(</span><span class="n">Color</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">PINK</span> <span class="o">=</span> <span class="mi">17</span>
<span class="gp">...</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">TypeError</span>: <span class="n">Cannot extend enumerations</span>
</pre></div>
</div>
<p>But this is allowed:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Foo</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">some_behavior</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">pass</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Bar</span><span class="p">(</span><span class="n">Foo</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">HAPPY</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">SAD</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">...</span>
</pre></div>
</div>
<p>Allowing subclassing of enums that define members would lead to a violation of
some important invariants of types and instances. On the other hand, it makes
sense to allow sharing some common behavior between a group of enumerations.
(See <a class="reference internal" href="#orderedenum">OrderedEnum</a> for an example.)</p>
</div>
<div class="section" id="pickling">
<h2>Pickling<a class="headerlink" href="#pickling" title="Permalink to this headline">¶</a></h2>
<p>Enumerations can be pickled and unpickled:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">test.test_enum</span> <span class="kn">import</span> <span class="n">Fruit</span>
<span class="gp">>>> </span><span class="kn">from</span> <span class="nn">pickle</span> <span class="kn">import</span> <span class="n">dumps</span><span class="p">,</span> <span class="n">loads</span>
<span class="gp">>>> </span><span class="n">Fruit</span><span class="o">.</span><span class="n">TOMATO</span> <span class="ow">is</span> <span class="n">loads</span><span class="p">(</span><span class="n">dumps</span><span class="p">(</span><span class="n">Fruit</span><span class="o">.</span><span class="n">TOMATO</span><span class="p">))</span>
<span class="go">True</span>
</pre></div>
</div>
<p>The usual restrictions for pickling apply: picklable enums must be defined in
the top level of a module, since unpickling requires them to be importable
from that module.</p>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>With pickle protocol version 4 it is possible to easily pickle enums
nested in other classes.</p>
</div>
<p>It is possible to modify how Enum members are pickled/unpickled by defining
<a class="reference internal" href="pickle.html#object.__reduce_ex__" title="object.__reduce_ex__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__reduce_ex__()</span></code></a> in the enumeration class.</p>
</div>
<div class="section" id="functional-api">
<h2>Functional API<a class="headerlink" href="#functional-api" title="Permalink to this headline">¶</a></h2>
<p>The <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> class is callable, providing the following functional API:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Animal</span> <span class="o">=</span> <span class="n">Enum</span><span class="p">(</span><span class="s1">'Animal'</span><span class="p">,</span> <span class="s1">'ANT BEE CAT DOG'</span><span class="p">)</span>
<span class="gp">>>> </span><span class="n">Animal</span>
<span class="go"><enum 'Animal'></span>
<span class="gp">>>> </span><span class="n">Animal</span><span class="o">.</span><span class="n">ANT</span>
<span class="go"><Animal.ANT: 1></span>
<span class="gp">>>> </span><span class="n">Animal</span><span class="o">.</span><span class="n">ANT</span><span class="o">.</span><span class="n">value</span>
<span class="go">1</span>
<span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">Animal</span><span class="p">)</span>
<span class="go">[<Animal.ANT: 1>, <Animal.BEE: 2>, <Animal.CAT: 3>, <Animal.DOG: 4>]</span>
</pre></div>
</div>
<p>The semantics of this API resemble <a class="reference internal" href="collections.html#collections.namedtuple" title="collections.namedtuple"><code class="xref py py-class docutils literal notranslate"><span class="pre">namedtuple</span></code></a>. The first
argument of the call to <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> is the name of the enumeration.</p>
<p>The second argument is the <em>source</em> of enumeration member names. It can be a
whitespace-separated string of names, a sequence of names, a sequence of
2-tuples with key/value pairs, or a mapping (e.g. dictionary) of names to
values. The last two options enable assigning arbitrary values to
enumerations; the others auto-assign increasing integers starting with 1 (use
the <code class="docutils literal notranslate"><span class="pre">start</span></code> parameter to specify a different starting value). A
new class derived from <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> is returned. In other words, the above
assignment to <code class="xref py py-class docutils literal notranslate"><span class="pre">Animal</span></code> is equivalent to:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Animal</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">ANT</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">BEE</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">... </span> <span class="n">CAT</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">... </span> <span class="n">DOG</span> <span class="o">=</span> <span class="mi">4</span>
<span class="gp">...</span>
</pre></div>
</div>
<p>The reason for defaulting to <code class="docutils literal notranslate"><span class="pre">1</span></code> as the starting number and not <code class="docutils literal notranslate"><span class="pre">0</span></code> is
that <code class="docutils literal notranslate"><span class="pre">0</span></code> is <code class="docutils literal notranslate"><span class="pre">False</span></code> in a boolean sense, but enum members all evaluate
to <code class="docutils literal notranslate"><span class="pre">True</span></code>.</p>
<p>Pickling enums created with the functional API can be tricky as frame stack
implementation details are used to try and figure out which module the
enumeration is being created in (e.g. it will fail if you use a utility
function in separate module, and also may not work on IronPython or Jython).
The solution is to specify the module name explicitly as follows:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Animal</span> <span class="o">=</span> <span class="n">Enum</span><span class="p">(</span><span class="s1">'Animal'</span><span class="p">,</span> <span class="s1">'ANT BEE CAT DOG'</span><span class="p">,</span> <span class="n">module</span><span class="o">=</span><span class="vm">__name__</span><span class="p">)</span>
</pre></div>
</div>
<div class="admonition warning">
<p class="admonition-title">Warning</p>
<p>If <code class="docutils literal notranslate"><span class="pre">module</span></code> is not supplied, and Enum cannot determine what it is,
the new Enum members will not be unpicklable; to keep errors closer to
the source, pickling will be disabled.</p>
</div>
<p>The new pickle protocol 4 also, in some circumstances, relies on
<a class="reference internal" href="stdtypes.html#definition.__qualname__" title="definition.__qualname__"><code class="xref py py-attr docutils literal notranslate"><span class="pre">__qualname__</span></code></a> being set to the location where pickle will be able
to find the class. For example, if the class was made available in class
SomeData in the global scope:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Animal</span> <span class="o">=</span> <span class="n">Enum</span><span class="p">(</span><span class="s1">'Animal'</span><span class="p">,</span> <span class="s1">'ANT BEE CAT DOG'</span><span class="p">,</span> <span class="n">qualname</span><span class="o">=</span><span class="s1">'SomeData.Animal'</span><span class="p">)</span>
</pre></div>
</div>
<p>The complete signature is:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">Enum</span><span class="p">(</span><span class="n">value</span><span class="o">=</span><span class="s1">'NewEnumName'</span><span class="p">,</span> <span class="n">names</span><span class="o">=<...></span><span class="p">,</span> <span class="o">*</span><span class="p">,</span> <span class="n">module</span><span class="o">=</span><span class="s1">'...'</span><span class="p">,</span> <span class="n">qualname</span><span class="o">=</span><span class="s1">'...'</span><span class="p">,</span> <span class="nb">type</span><span class="o">=<</span><span class="n">mixed</span><span class="o">-</span><span class="ow">in</span> <span class="n">class</span><span class="o">></span><span class="p">,</span> <span class="n">start</span><span class="o">=</span><span class="mi">1</span><span class="p">)</span>
</pre></div>
</div>
<dl class="field-list">
<dt class="field-odd">value</dt>
<dd class="field-odd"><p>What the new Enum class will record as its name.</p>
</dd>
<dt class="field-even">names</dt>
<dd class="field-even"><p>The Enum members. This can be a whitespace or comma separated string
(values will start at 1 unless otherwise specified):</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="s1">'RED GREEN BLUE'</span> <span class="o">|</span> <span class="s1">'RED,GREEN,BLUE'</span> <span class="o">|</span> <span class="s1">'RED, GREEN, BLUE'</span>
</pre></div>
</div>
<p>or an iterator of names:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="p">[</span><span class="s1">'RED'</span><span class="p">,</span> <span class="s1">'GREEN'</span><span class="p">,</span> <span class="s1">'BLUE'</span><span class="p">]</span>
</pre></div>
</div>
<p>or an iterator of (name, value) pairs:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="p">[(</span><span class="s1">'CYAN'</span><span class="p">,</span> <span class="mi">4</span><span class="p">),</span> <span class="p">(</span><span class="s1">'MAGENTA'</span><span class="p">,</span> <span class="mi">5</span><span class="p">),</span> <span class="p">(</span><span class="s1">'YELLOW'</span><span class="p">,</span> <span class="mi">6</span><span class="p">)]</span>
</pre></div>
</div>
<p>or a mapping:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="p">{</span><span class="s1">'CHARTREUSE'</span><span class="p">:</span> <span class="mi">7</span><span class="p">,</span> <span class="s1">'SEA_GREEN'</span><span class="p">:</span> <span class="mi">11</span><span class="p">,</span> <span class="s1">'ROSEMARY'</span><span class="p">:</span> <span class="mi">42</span><span class="p">}</span>
</pre></div>
</div>
</dd>
<dt class="field-odd">module</dt>
<dd class="field-odd"><p>name of module where new Enum class can be found.</p>
</dd>
<dt class="field-even">qualname</dt>
<dd class="field-even"><p>where in module new Enum class can be found.</p>
</dd>
<dt class="field-odd">type</dt>
<dd class="field-odd"><p>type to mix in to new Enum class.</p>
</dd>
<dt class="field-even">start</dt>
<dd class="field-even"><p>number to start counting at if only names are passed in.</p>
</dd>
</dl>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.5: </span>The <em>start</em> parameter was added.</p>
</div>
</div>
<div class="section" id="derived-enumerations">
<h2>Derived Enumerations<a class="headerlink" href="#derived-enumerations" title="Permalink to this headline">¶</a></h2>
<div class="section" id="intenum">
<h3>IntEnum<a class="headerlink" href="#intenum" title="Permalink to this headline">¶</a></h3>
<p>The first variation of <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> that is provided is also a subclass of
<a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>. Members of an <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntEnum</span></code></a> can be compared to integers;
by extension, integer enumerations of different types can also be compared
to each other:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">enum</span> <span class="kn">import</span> <span class="n">IntEnum</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Shape</span><span class="p">(</span><span class="n">IntEnum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">CIRCLE</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">SQUARE</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Request</span><span class="p">(</span><span class="n">IntEnum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">POST</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">GET</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Shape</span> <span class="o">==</span> <span class="mi">1</span>
<span class="go">False</span>
<span class="gp">>>> </span><span class="n">Shape</span><span class="o">.</span><span class="n">CIRCLE</span> <span class="o">==</span> <span class="mi">1</span>
<span class="go">True</span>
<span class="gp">>>> </span><span class="n">Shape</span><span class="o">.</span><span class="n">CIRCLE</span> <span class="o">==</span> <span class="n">Request</span><span class="o">.</span><span class="n">POST</span>
<span class="go">True</span>
</pre></div>
</div>
<p>However, they still can’t be compared to standard <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> enumerations:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Shape</span><span class="p">(</span><span class="n">IntEnum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">CIRCLE</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">SQUARE</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Shape</span><span class="o">.</span><span class="n">CIRCLE</span> <span class="o">==</span> <span class="n">Color</span><span class="o">.</span><span class="n">RED</span>
<span class="go">False</span>
</pre></div>
</div>
<p><a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntEnum</span></code></a> values behave like integers in other ways you’d expect:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">int</span><span class="p">(</span><span class="n">Shape</span><span class="o">.</span><span class="n">CIRCLE</span><span class="p">)</span>
<span class="go">1</span>
<span class="gp">>>> </span><span class="p">[</span><span class="s1">'a'</span><span class="p">,</span> <span class="s1">'b'</span><span class="p">,</span> <span class="s1">'c'</span><span class="p">][</span><span class="n">Shape</span><span class="o">.</span><span class="n">CIRCLE</span><span class="p">]</span>
<span class="go">'b'</span>
<span class="gp">>>> </span><span class="p">[</span><span class="n">i</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="n">Shape</span><span class="o">.</span><span class="n">SQUARE</span><span class="p">)]</span>
<span class="go">[0, 1]</span>
</pre></div>
</div>
</div>
<div class="section" id="intflag">
<h3>IntFlag<a class="headerlink" href="#intflag" title="Permalink to this headline">¶</a></h3>
<p>The next variation of <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> provided, <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a>, is also based
on <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>. The difference being <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a> members can be combined
using the bitwise operators (&, |, ^, ~) and the result is still an
<a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a> member. However, as the name implies, <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a>
members also subclass <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a> and can be used wherever an <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a> is
used. Any operation on an <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a> member besides the bit-wise
operations will lose the <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a> membership.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.6.</span></p>
</div>
<p>Sample <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a> class:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">enum</span> <span class="kn">import</span> <span class="n">IntFlag</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Perm</span><span class="p">(</span><span class="n">IntFlag</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">R</span> <span class="o">=</span> <span class="mi">4</span>
<span class="gp">... </span> <span class="n">W</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">... </span> <span class="n">X</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Perm</span><span class="o">.</span><span class="n">R</span> <span class="o">|</span> <span class="n">Perm</span><span class="o">.</span><span class="n">W</span>
<span class="go"><Perm.R|W: 6></span>
<span class="gp">>>> </span><span class="n">Perm</span><span class="o">.</span><span class="n">R</span> <span class="o">+</span> <span class="n">Perm</span><span class="o">.</span><span class="n">W</span>
<span class="go">6</span>
<span class="gp">>>> </span><span class="n">RW</span> <span class="o">=</span> <span class="n">Perm</span><span class="o">.</span><span class="n">R</span> <span class="o">|</span> <span class="n">Perm</span><span class="o">.</span><span class="n">W</span>
<span class="gp">>>> </span><span class="n">Perm</span><span class="o">.</span><span class="n">R</span> <span class="ow">in</span> <span class="n">RW</span>
<span class="go">True</span>
</pre></div>
</div>
<p>It is also possible to name the combinations:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Perm</span><span class="p">(</span><span class="n">IntFlag</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">R</span> <span class="o">=</span> <span class="mi">4</span>
<span class="gp">... </span> <span class="n">W</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">... </span> <span class="n">X</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">RWX</span> <span class="o">=</span> <span class="mi">7</span>
<span class="gp">>>> </span><span class="n">Perm</span><span class="o">.</span><span class="n">RWX</span>
<span class="go"><Perm.RWX: 7></span>
<span class="gp">>>> </span><span class="o">~</span><span class="n">Perm</span><span class="o">.</span><span class="n">RWX</span>
<span class="go"><Perm.-8: -8></span>
</pre></div>
</div>
<p>Another important difference between <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a> and <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> is that
if no flags are set (the value is 0), its boolean evaluation is <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-data docutils literal notranslate"><span class="pre">False</span></code></a>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Perm</span><span class="o">.</span><span class="n">R</span> <span class="o">&</span> <span class="n">Perm</span><span class="o">.</span><span class="n">X</span>
<span class="go"><Perm.0: 0></span>
<span class="gp">>>> </span><span class="nb">bool</span><span class="p">(</span><span class="n">Perm</span><span class="o">.</span><span class="n">R</span> <span class="o">&</span> <span class="n">Perm</span><span class="o">.</span><span class="n">X</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
</div>
<p>Because <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a> members are also subclasses of <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a> they can
be combined with them:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="n">Perm</span><span class="o">.</span><span class="n">X</span> <span class="o">|</span> <span class="mi">8</span>
<span class="go"><Perm.8|X: 9></span>
</pre></div>
</div>
</div>
<div class="section" id="flag">
<h3>Flag<a class="headerlink" href="#flag" title="Permalink to this headline">¶</a></h3>
<p>The last variation is <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate"><span class="pre">Flag</span></code></a>. Like <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a>, <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate"><span class="pre">Flag</span></code></a>
members can be combined using the bitwise operators (&, |, ^, ~). Unlike
<a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a>, they cannot be combined with, nor compared against, any
other <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate"><span class="pre">Flag</span></code></a> enumeration, nor <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>. While it is possible to
specify the values directly it is recommended to use <a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate"><span class="pre">auto</span></code></a> as the
value and let <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate"><span class="pre">Flag</span></code></a> select an appropriate value.</p>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.6.</span></p>
</div>
<p>Like <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a>, if a combination of <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate"><span class="pre">Flag</span></code></a> members results in no
flags being set, the boolean evaluation is <a class="reference internal" href="constants.html#False" title="False"><code class="xref py py-data docutils literal notranslate"><span class="pre">False</span></code></a>:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">enum</span> <span class="kn">import</span> <span class="n">Flag</span><span class="p">,</span> <span class="n">auto</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">Flag</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span> <span class="o">&</span> <span class="n">Color</span><span class="o">.</span><span class="n">GREEN</span>
<span class="go"><Color.0: 0></span>
<span class="gp">>>> </span><span class="nb">bool</span><span class="p">(</span><span class="n">Color</span><span class="o">.</span><span class="n">RED</span> <span class="o">&</span> <span class="n">Color</span><span class="o">.</span><span class="n">GREEN</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
</div>
<p>Individual flags should have values that are powers of two (1, 2, 4, 8, …),
while combinations of flags won’t:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">Flag</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">WHITE</span> <span class="o">=</span> <span class="n">RED</span> <span class="o">|</span> <span class="n">BLUE</span> <span class="o">|</span> <span class="n">GREEN</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">WHITE</span>
<span class="go"><Color.WHITE: 7></span>
</pre></div>
</div>
<p>Giving a name to the “no flags set” condition does not change its boolean
value:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">Flag</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">BLACK</span> <span class="o">=</span> <span class="mi">0</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">BLACK</span>
<span class="go"><Color.BLACK: 0></span>
<span class="gp">>>> </span><span class="nb">bool</span><span class="p">(</span><span class="n">Color</span><span class="o">.</span><span class="n">BLACK</span><span class="p">)</span>
<span class="go">False</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>For the majority of new code, <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> and <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate"><span class="pre">Flag</span></code></a> are strongly
recommended, since <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntEnum</span></code></a> and <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a> break some
semantic promises of an enumeration (by being comparable to integers, and
thus by transitivity to other unrelated enumerations). <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntEnum</span></code></a>
and <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a> should be used only in cases where <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> and
<a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate"><span class="pre">Flag</span></code></a> will not do; for example, when integer constants are replaced
with enumerations, or for interoperability with other systems.</p>
</div>
</div>
<div class="section" id="others">
<h3>Others<a class="headerlink" href="#others" title="Permalink to this headline">¶</a></h3>
<p>While <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntEnum</span></code></a> is part of the <a class="reference internal" href="#module-enum" title="enum: Implementation of an enumeration class."><code class="xref py py-mod docutils literal notranslate"><span class="pre">enum</span></code></a> module, it would be very
simple to implement independently:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">IntEnum</span><span class="p">(</span><span class="nb">int</span><span class="p">,</span> <span class="n">Enum</span><span class="p">):</span>
<span class="k">pass</span>
</pre></div>
</div>
<p>This demonstrates how similar derived enumerations can be defined; for example
a <code class="xref py py-class docutils literal notranslate"><span class="pre">StrEnum</span></code> that mixes in <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a> instead of <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>.</p>
<p>Some rules:</p>
<ol class="arabic simple">
<li><p>When subclassing <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a>, mix-in types must appear before
<a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> itself in the sequence of bases, as in the <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntEnum</span></code></a>
example above.</p></li>
<li><p>While <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> can have members of any type, once you mix in an
additional type, all the members must have values of that type, e.g.
<a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a> above. This restriction does not apply to mix-ins which only
add methods and don’t specify another data type such as <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a> or
<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>.</p></li>
<li><p>When another data type is mixed in, the <code class="xref py py-attr docutils literal notranslate"><span class="pre">value</span></code> attribute is <em>not the
same</em> as the enum member itself, although it is equivalent and will compare
equal.</p></li>
<li><p>%-style formatting: <cite>%s</cite> and <cite>%r</cite> call the <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> class’s
<a class="reference internal" href="../reference/datamodel.html#object.__str__" title="object.__str__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__str__()</span></code></a> and <a class="reference internal" href="../reference/datamodel.html#object.__repr__" title="object.__repr__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__repr__()</span></code></a> respectively; other codes (such as
<cite>%i</cite> or <cite>%h</cite> for IntEnum) treat the enum member as its mixed-in type.</p></li>
<li><p><a class="reference internal" href="../reference/lexical_analysis.html#f-strings"><span class="std std-ref">Formatted string literals</span></a>, <a class="reference internal" href="stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate"><span class="pre">str.format()</span></code></a>,
and <a class="reference internal" href="functions.html#format" title="format"><code class="xref py py-func docutils literal notranslate"><span class="pre">format()</span></code></a> will use the mixed-in
type’s <a class="reference internal" href="../reference/datamodel.html#object.__format__" title="object.__format__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__format__()</span></code></a>. If the <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> class’s <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate"><span class="pre">str()</span></code></a> or
<a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a> is desired, use the <cite>!s</cite> or <cite>!r</cite> format codes.</p></li>
</ol>
</div>
</div>
<div class="section" id="interesting-examples">
<h2>Interesting examples<a class="headerlink" href="#interesting-examples" title="Permalink to this headline">¶</a></h2>
<p>While <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a>, <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntEnum</span></code></a>, <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntFlag</span></code></a>, and <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate"><span class="pre">Flag</span></code></a> are
expected to cover the majority of use-cases, they cannot cover them all. Here
are recipes for some different types of enumerations that can be used directly,
or as examples for creating one’s own.</p>
<div class="section" id="omitting-values">
<h3>Omitting values<a class="headerlink" href="#omitting-values" title="Permalink to this headline">¶</a></h3>
<p>In many use-cases one doesn’t care what the actual value of an enumeration
is. There are several ways to define this type of simple enumeration:</p>
<ul class="simple">
<li><p>use instances of <a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate"><span class="pre">auto</span></code></a> for the value</p></li>
<li><p>use instances of <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate"><span class="pre">object</span></code></a> as the value</p></li>
<li><p>use a descriptive string as the value</p></li>
<li><p>use a tuple as the value and a custom <a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__new__()</span></code></a> to replace the
tuple with an <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a> value</p></li>
</ul>
<p>Using any of these methods signifies to the user that these values are not
important, and also enables one to add, remove, or reorder members without
having to renumber the remaining members.</p>
<p>Whichever method you choose, you should provide a <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-meth docutils literal notranslate"><span class="pre">repr()</span></code></a> that also hides
the (unimportant) value:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">NoValue</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span> <span class="fm">__repr__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">return</span> <span class="s1">'<</span><span class="si">%s</span><span class="s1">.</span><span class="si">%s</span><span class="s1">>'</span> <span class="o">%</span> <span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="vm">__class__</span><span class="o">.</span><span class="vm">__name__</span><span class="p">,</span> <span class="bp">self</span><span class="o">.</span><span class="n">name</span><span class="p">)</span>
<span class="gp">...</span>
</pre></div>
</div>
<div class="section" id="using-auto">
<h4>Using <a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate"><span class="pre">auto</span></code></a><a class="headerlink" href="#using-auto" title="Permalink to this headline">¶</a></h4>
<p>Using <a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate"><span class="pre">auto</span></code></a> would look like:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">NoValue</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">GREEN</span>
<span class="go"><Color.GREEN></span>
</pre></div>
</div>
</div>
<div class="section" id="using-object">
<h4>Using <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate"><span class="pre">object</span></code></a><a class="headerlink" href="#using-object" title="Permalink to this headline">¶</a></h4>
<p>Using <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate"><span class="pre">object</span></code></a> would look like:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">NoValue</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="nb">object</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="nb">object</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="nb">object</span><span class="p">()</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">GREEN</span>
<span class="go"><Color.GREEN></span>
</pre></div>
</div>
</div>
<div class="section" id="using-a-descriptive-string">
<h4>Using a descriptive string<a class="headerlink" href="#using-a-descriptive-string" title="Permalink to this headline">¶</a></h4>
<p>Using a string as the value would look like:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">NoValue</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="s1">'stop'</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="s1">'go'</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="s1">'too fast!'</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">GREEN</span>
<span class="go"><Color.GREEN></span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">GREEN</span><span class="o">.</span><span class="n">value</span>
<span class="go">'go'</span>
</pre></div>
</div>
</div>
<div class="section" id="using-a-custom-new">
<h4>Using a custom <a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__new__()</span></code></a><a class="headerlink" href="#using-a-custom-new" title="Permalink to this headline">¶</a></h4>
<p>Using an auto-numbering <a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__new__()</span></code></a> would look like:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">AutoNumber</span><span class="p">(</span><span class="n">NoValue</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span> <span class="fm">__new__</span><span class="p">(</span><span class="bp">cls</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">value</span> <span class="o">=</span> <span class="nb">len</span><span class="p">(</span><span class="bp">cls</span><span class="o">.</span><span class="n">__members__</span><span class="p">)</span> <span class="o">+</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">obj</span> <span class="o">=</span> <span class="nb">object</span><span class="o">.</span><span class="fm">__new__</span><span class="p">(</span><span class="bp">cls</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">obj</span><span class="o">.</span><span class="n">_value_</span> <span class="o">=</span> <span class="n">value</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">obj</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">AutoNumber</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="p">()</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="p">()</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="p">()</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">GREEN</span>
<span class="go"><Color.GREEN></span>
<span class="gp">>>> </span><span class="n">Color</span><span class="o">.</span><span class="n">GREEN</span><span class="o">.</span><span class="n">value</span>
<span class="go">2</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>The <a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__new__()</span></code></a> method, if defined, is used during creation of the Enum
members; it is then replaced by Enum’s <a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__new__()</span></code></a> which is used after
class creation for lookup of existing members.</p>
</div>
</div>
</div>
<div class="section" id="orderedenum">
<h3>OrderedEnum<a class="headerlink" href="#orderedenum" title="Permalink to this headline">¶</a></h3>
<p>An ordered enumeration that is not based on <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate"><span class="pre">IntEnum</span></code></a> and so maintains
the normal <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> invariants (such as not being comparable to other
enumerations):</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">OrderedEnum</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span> <span class="fm">__ge__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">other</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="vm">__class__</span> <span class="ow">is</span> <span class="n">other</span><span class="o">.</span><span class="vm">__class__</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">value</span> <span class="o">>=</span> <span class="n">other</span><span class="o">.</span><span class="n">value</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">NotImplemented</span>
<span class="gp">... </span> <span class="k">def</span> <span class="fm">__gt__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">other</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="vm">__class__</span> <span class="ow">is</span> <span class="n">other</span><span class="o">.</span><span class="vm">__class__</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">value</span> <span class="o">></span> <span class="n">other</span><span class="o">.</span><span class="n">value</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">NotImplemented</span>
<span class="gp">... </span> <span class="k">def</span> <span class="fm">__le__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">other</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="vm">__class__</span> <span class="ow">is</span> <span class="n">other</span><span class="o">.</span><span class="vm">__class__</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">value</span> <span class="o"><=</span> <span class="n">other</span><span class="o">.</span><span class="n">value</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">NotImplemented</span>
<span class="gp">... </span> <span class="k">def</span> <span class="fm">__lt__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">other</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">if</span> <span class="bp">self</span><span class="o">.</span><span class="vm">__class__</span> <span class="ow">is</span> <span class="n">other</span><span class="o">.</span><span class="vm">__class__</span><span class="p">:</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">value</span> <span class="o"><</span> <span class="n">other</span><span class="o">.</span><span class="n">value</span>
<span class="gp">... </span> <span class="k">return</span> <span class="bp">NotImplemented</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Grade</span><span class="p">(</span><span class="n">OrderedEnum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">A</span> <span class="o">=</span> <span class="mi">5</span>
<span class="gp">... </span> <span class="n">B</span> <span class="o">=</span> <span class="mi">4</span>
<span class="gp">... </span> <span class="n">C</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">... </span> <span class="n">D</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">... </span> <span class="n">F</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Grade</span><span class="o">.</span><span class="n">C</span> <span class="o"><</span> <span class="n">Grade</span><span class="o">.</span><span class="n">A</span>
<span class="go">True</span>
</pre></div>
</div>
</div>
<div class="section" id="duplicatefreeenum">
<h3>DuplicateFreeEnum<a class="headerlink" href="#duplicatefreeenum" title="Permalink to this headline">¶</a></h3>
<p>Raises an error if a duplicate member name is found instead of creating an
alias:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">DuplicateFreeEnum</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="o">*</span><span class="n">args</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">cls</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="vm">__class__</span>
<span class="gp">... </span> <span class="k">if</span> <span class="nb">any</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">value</span> <span class="o">==</span> <span class="n">e</span><span class="o">.</span><span class="n">value</span> <span class="k">for</span> <span class="n">e</span> <span class="ow">in</span> <span class="bp">cls</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">a</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">name</span>
<span class="gp">... </span> <span class="n">e</span> <span class="o">=</span> <span class="bp">cls</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">value</span><span class="p">)</span><span class="o">.</span><span class="n">name</span>
<span class="gp">... </span> <span class="k">raise</span> <span class="ne">ValueError</span><span class="p">(</span>
<span class="gp">... </span> <span class="s2">"aliases not allowed in DuplicateFreeEnum: </span><span class="si">%r</span><span class="s2"> --> </span><span class="si">%r</span><span class="s2">"</span>
<span class="gp">... </span> <span class="o">%</span> <span class="p">(</span><span class="n">a</span><span class="p">,</span> <span class="n">e</span><span class="p">))</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">DuplicateFreeEnum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">... </span> <span class="n">GRENE</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">...</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">ValueError</span>: <span class="n">aliases not allowed in DuplicateFreeEnum: 'GRENE' --> 'GREEN'</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>This is a useful example for subclassing Enum to add or change other
behaviors as well as disallowing aliases. If the only desired change is
disallowing aliases, the <a class="reference internal" href="#enum.unique" title="enum.unique"><code class="xref py py-func docutils literal notranslate"><span class="pre">unique()</span></code></a> decorator can be used instead.</p>
</div>
</div>
<div class="section" id="planet">
<h3>Planet<a class="headerlink" href="#planet" title="Permalink to this headline">¶</a></h3>
<p>If <a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__new__()</span></code></a> or <a class="reference internal" href="../reference/datamodel.html#object.__init__" title="object.__init__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__init__()</span></code></a> is defined the value of the enum member
will be passed to those methods:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Planet</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">MERCURY</span> <span class="o">=</span> <span class="p">(</span><span class="mf">3.303e+23</span><span class="p">,</span> <span class="mf">2.4397e6</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">VENUS</span> <span class="o">=</span> <span class="p">(</span><span class="mf">4.869e+24</span><span class="p">,</span> <span class="mf">6.0518e6</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">EARTH</span> <span class="o">=</span> <span class="p">(</span><span class="mf">5.976e+24</span><span class="p">,</span> <span class="mf">6.37814e6</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">MARS</span> <span class="o">=</span> <span class="p">(</span><span class="mf">6.421e+23</span><span class="p">,</span> <span class="mf">3.3972e6</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">JUPITER</span> <span class="o">=</span> <span class="p">(</span><span class="mf">1.9e+27</span><span class="p">,</span> <span class="mf">7.1492e7</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">SATURN</span> <span class="o">=</span> <span class="p">(</span><span class="mf">5.688e+26</span><span class="p">,</span> <span class="mf">6.0268e7</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">URANUS</span> <span class="o">=</span> <span class="p">(</span><span class="mf">8.686e+25</span><span class="p">,</span> <span class="mf">2.5559e7</span><span class="p">)</span>
<span class="gp">... </span> <span class="n">NEPTUNE</span> <span class="o">=</span> <span class="p">(</span><span class="mf">1.024e+26</span><span class="p">,</span> <span class="mf">2.4746e7</span><span class="p">)</span>
<span class="gp">... </span> <span class="k">def</span> <span class="fm">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span> <span class="n">mass</span><span class="p">,</span> <span class="n">radius</span><span class="p">):</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">mass</span> <span class="o">=</span> <span class="n">mass</span> <span class="c1"># in kilograms</span>
<span class="gp">... </span> <span class="bp">self</span><span class="o">.</span><span class="n">radius</span> <span class="o">=</span> <span class="n">radius</span> <span class="c1"># in meters</span>
<span class="gp">... </span> <span class="nd">@property</span>
<span class="gp">... </span> <span class="k">def</span> <span class="nf">surface_gravity</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="gp">... </span> <span class="c1"># universal gravitational constant (m3 kg-1 s-2)</span>
<span class="gp">... </span> <span class="n">G</span> <span class="o">=</span> <span class="mf">6.67300E-11</span>
<span class="gp">... </span> <span class="k">return</span> <span class="n">G</span> <span class="o">*</span> <span class="bp">self</span><span class="o">.</span><span class="n">mass</span> <span class="o">/</span> <span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">radius</span> <span class="o">*</span> <span class="bp">self</span><span class="o">.</span><span class="n">radius</span><span class="p">)</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Planet</span><span class="o">.</span><span class="n">EARTH</span><span class="o">.</span><span class="n">value</span>
<span class="go">(5.976e+24, 6378140.0)</span>
<span class="gp">>>> </span><span class="n">Planet</span><span class="o">.</span><span class="n">EARTH</span><span class="o">.</span><span class="n">surface_gravity</span>
<span class="go">9.802652743337129</span>
</pre></div>
</div>
</div>
<div class="section" id="timeperiod">
<h3>TimePeriod<a class="headerlink" href="#timeperiod" title="Permalink to this headline">¶</a></h3>
<p>An example to show the <code class="xref py py-attr docutils literal notranslate"><span class="pre">_ignore_</span></code> attribute in use:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="kn">from</span> <span class="nn">datetime</span> <span class="kn">import</span> <span class="n">timedelta</span>
<span class="gp">>>> </span><span class="k">class</span> <span class="nc">Period</span><span class="p">(</span><span class="n">timedelta</span><span class="p">,</span> <span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="s2">"different lengths of time"</span>
<span class="gp">... </span> <span class="n">_ignore_</span> <span class="o">=</span> <span class="s1">'Period i'</span>
<span class="gp">... </span> <span class="n">Period</span> <span class="o">=</span> <span class="nb">vars</span><span class="p">()</span>
<span class="gp">... </span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">367</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">Period</span><span class="p">[</span><span class="s1">'day_</span><span class="si">%d</span><span class="s1">'</span> <span class="o">%</span> <span class="n">i</span><span class="p">]</span> <span class="o">=</span> <span class="n">i</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">Period</span><span class="p">)[:</span><span class="mi">2</span><span class="p">]</span>
<span class="go">[<Period.day_0: datetime.timedelta(0)>, <Period.day_1: datetime.timedelta(days=1)>]</span>
<span class="gp">>>> </span><span class="nb">list</span><span class="p">(</span><span class="n">Period</span><span class="p">)[</span><span class="o">-</span><span class="mi">2</span><span class="p">:]</span>
<span class="go">[<Period.day_365: datetime.timedelta(days=365)>, <Period.day_366: datetime.timedelta(days=366)>]</span>
</pre></div>
</div>
</div>
</div>
<div class="section" id="how-are-enums-different">
<h2>How are Enums different?<a class="headerlink" href="#how-are-enums-different" title="Permalink to this headline">¶</a></h2>
<p>Enums have a custom metaclass that affects many aspects of both derived Enum
classes and their instances (members).</p>
<div class="section" id="enum-classes">
<h3>Enum Classes<a class="headerlink" href="#enum-classes" title="Permalink to this headline">¶</a></h3>
<p>The <code class="xref py py-class docutils literal notranslate"><span class="pre">EnumMeta</span></code> metaclass is responsible for providing the
<a class="reference internal" href="../reference/datamodel.html#object.__contains__" title="object.__contains__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__contains__()</span></code></a>, <a class="reference internal" href="../reference/datamodel.html#object.__dir__" title="object.__dir__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__dir__()</span></code></a>, <a class="reference internal" href="../reference/datamodel.html#object.__iter__" title="object.__iter__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__iter__()</span></code></a> and other methods that
allow one to do things with an <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> class that fail on a typical
class, such as <cite>list(Color)</cite> or <cite>some_enum_var in Color</cite>. <code class="xref py py-class docutils literal notranslate"><span class="pre">EnumMeta</span></code> is
responsible for ensuring that various other methods on the final <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a>
class are correct (such as <a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__new__()</span></code></a>, <a class="reference internal" href="pickle.html#object.__getnewargs__" title="object.__getnewargs__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__getnewargs__()</span></code></a>,
<a class="reference internal" href="../reference/datamodel.html#object.__str__" title="object.__str__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__str__()</span></code></a> and <a class="reference internal" href="../reference/datamodel.html#object.__repr__" title="object.__repr__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__repr__()</span></code></a>).</p>
</div>
<div class="section" id="enum-members-aka-instances">
<h3>Enum Members (aka instances)<a class="headerlink" href="#enum-members-aka-instances" title="Permalink to this headline">¶</a></h3>
<p>The most interesting thing about Enum members is that they are singletons.
<code class="xref py py-class docutils literal notranslate"><span class="pre">EnumMeta</span></code> creates them all while it is creating the <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a>
class itself, and then puts a custom <a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__new__()</span></code></a> in place to ensure
that no new ones are ever instantiated by returning only the existing
member instances.</p>
</div>
<div class="section" id="finer-points">
<h3>Finer Points<a class="headerlink" href="#finer-points" title="Permalink to this headline">¶</a></h3>
<div class="section" id="supported-dunder-names">
<h4>Supported <code class="docutils literal notranslate"><span class="pre">__dunder__</span></code> names<a class="headerlink" href="#supported-dunder-names" title="Permalink to this headline">¶</a></h4>
<p><code class="xref py py-attr docutils literal notranslate"><span class="pre">__members__</span></code> is an <code class="xref py py-class docutils literal notranslate"><span class="pre">OrderedDict</span></code> of <code class="docutils literal notranslate"><span class="pre">member_name</span></code>:<code class="docutils literal notranslate"><span class="pre">member</span></code>
items. It is only available on the class.</p>
<p><a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate"><span class="pre">__new__()</span></code></a>, if specified, must create and return the enum members; it is
also a very good idea to set the member’s <code class="xref py py-attr docutils literal notranslate"><span class="pre">_value_</span></code> appropriately. Once
all the members are created it is no longer used.</p>
</div>
<div class="section" id="supported-sunder-names">
<h4>Supported <code class="docutils literal notranslate"><span class="pre">_sunder_</span></code> names<a class="headerlink" href="#supported-sunder-names" title="Permalink to this headline">¶</a></h4>
<ul class="simple">
<li><p><code class="docutils literal notranslate"><span class="pre">_name_</span></code> – name of the member</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">_value_</span></code> – value of the member; can be set / modified in <code class="docutils literal notranslate"><span class="pre">__new__</span></code></p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">_missing_</span></code> – a lookup function used when a value is not found; may be
overridden</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">_ignore_</span></code> – a list of names, either as a <a class="reference internal" href="stdtypes.html#list" title="list"><code class="xref py py-func docutils literal notranslate"><span class="pre">list()</span></code></a> or a <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate"><span class="pre">str()</span></code></a>,
that will not be transformed into members, and will be removed from the final
class</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">_order_</span></code> – used in Python 2/3 code to ensure member order is consistent
(class attribute, removed during class creation)</p></li>
<li><p><code class="docutils literal notranslate"><span class="pre">_generate_next_value_</span></code> – used by the <a class="reference internal" href="#functional-api">Functional API</a> and by
<a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate"><span class="pre">auto</span></code></a> to get an appropriate value for an enum member; may be
overridden</p></li>
</ul>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.6: </span><code class="docutils literal notranslate"><span class="pre">_missing_</span></code>, <code class="docutils literal notranslate"><span class="pre">_order_</span></code>, <code class="docutils literal notranslate"><span class="pre">_generate_next_value_</span></code></p>
</div>
<div class="versionadded">
<p><span class="versionmodified added">New in version 3.7: </span><code class="docutils literal notranslate"><span class="pre">_ignore_</span></code></p>
</div>
<p>To help keep Python 2 / Python 3 code in sync an <code class="xref py py-attr docutils literal notranslate"><span class="pre">_order_</span></code> attribute can
be provided. It will be checked against the actual order of the enumeration
and raise an error if the two do not match:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">_order_</span> <span class="o">=</span> <span class="s1">'RED GREEN BLUE'</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="mi">3</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">...</span>
<span class="gt">Traceback (most recent call last):</span>
<span class="c">...</span>
<span class="gr">TypeError</span>: <span class="n">member order does not match _order_</span>
</pre></div>
</div>
<div class="admonition note">
<p class="admonition-title">Note</p>
<p>In Python 2 code the <code class="xref py py-attr docutils literal notranslate"><span class="pre">_order_</span></code> attribute is necessary as definition
order is lost before it can be recorded.</p>
</div>
</div>
<div class="section" id="enum-member-type">
<h4><code class="docutils literal notranslate"><span class="pre">Enum</span></code> member type<a class="headerlink" href="#enum-member-type" title="Permalink to this headline">¶</a></h4>
<p><a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> members are instances of their <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> class, and are
normally accessed as <code class="docutils literal notranslate"><span class="pre">EnumClass.member</span></code>. Under certain circumstances they
can also be accessed as <code class="docutils literal notranslate"><span class="pre">EnumClass.member.member</span></code>, but you should never do
this as that lookup may fail or, worse, return something besides the
<a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> member you are looking for (this is another good reason to use
all-uppercase names for members):</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">FieldTypes</span><span class="p">(</span><span class="n">Enum</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">name</span> <span class="o">=</span> <span class="mi">0</span>
<span class="gp">... </span> <span class="n">value</span> <span class="o">=</span> <span class="mi">1</span>
<span class="gp">... </span> <span class="n">size</span> <span class="o">=</span> <span class="mi">2</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">FieldTypes</span><span class="o">.</span><span class="n">value</span><span class="o">.</span><span class="n">size</span>
<span class="go"><FieldTypes.size: 2></span>
<span class="gp">>>> </span><span class="n">FieldTypes</span><span class="o">.</span><span class="n">size</span><span class="o">.</span><span class="n">value</span>
<span class="go">2</span>
</pre></div>
</div>
<div class="versionchanged">
<p><span class="versionmodified changed">Changed in version 3.5.</span></p>
</div>
</div>
<div class="section" id="boolean-value-of-enum-classes-and-members">
<h4>Boolean value of <code class="docutils literal notranslate"><span class="pre">Enum</span></code> classes and members<a class="headerlink" href="#boolean-value-of-enum-classes-and-members" title="Permalink to this headline">¶</a></h4>
<p><a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> members that are mixed with non-<a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> types (such as
<a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate"><span class="pre">int</span></code></a>, <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate"><span class="pre">str</span></code></a>, etc.) are evaluated according to the mixed-in
type’s rules; otherwise, all members evaluate as <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-data docutils literal notranslate"><span class="pre">True</span></code></a>. To make your
own Enum’s boolean evaluation depend on the member’s value add the following to
your class:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="fm">__bool__</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
<span class="k">return</span> <span class="nb">bool</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">value</span><span class="p">)</span>
</pre></div>
</div>
<p><a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> classes always evaluate as <a class="reference internal" href="constants.html#True" title="True"><code class="xref py py-data docutils literal notranslate"><span class="pre">True</span></code></a>.</p>
</div>
<div class="section" id="enum-classes-with-methods">
<h4><code class="docutils literal notranslate"><span class="pre">Enum</span></code> classes with methods<a class="headerlink" href="#enum-classes-with-methods" title="Permalink to this headline">¶</a></h4>
<p>If you give your <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate"><span class="pre">Enum</span></code></a> subclass extra methods, like the <a class="reference internal" href="#planet">Planet</a>
class above, those methods will show up in a <a class="reference internal" href="functions.html#dir" title="dir"><code class="xref py py-func docutils literal notranslate"><span class="pre">dir()</span></code></a> of the member,
but not of the class:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="nb">dir</span><span class="p">(</span><span class="n">Planet</span><span class="p">)</span>
<span class="go">['EARTH', 'JUPITER', 'MARS', 'MERCURY', 'NEPTUNE', 'SATURN', 'URANUS', 'VENUS', '__class__', '__doc__', '__members__', '__module__']</span>
<span class="gp">>>> </span><span class="nb">dir</span><span class="p">(</span><span class="n">Planet</span><span class="o">.</span><span class="n">EARTH</span><span class="p">)</span>
<span class="go">['__class__', '__doc__', '__module__', 'name', 'surface_gravity', 'value']</span>
</pre></div>
</div>
</div>
<div class="section" id="combining-members-of-flag">
<h4>Combining members of <code class="docutils literal notranslate"><span class="pre">Flag</span></code><a class="headerlink" href="#combining-members-of-flag" title="Permalink to this headline">¶</a></h4>
<p>If a combination of Flag members is not named, the <a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code></a> will include
all named flags and all named combinations of flags that are in the value:</p>
<div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="gp">>>> </span><span class="k">class</span> <span class="nc">Color</span><span class="p">(</span><span class="n">Flag</span><span class="p">):</span>
<span class="gp">... </span> <span class="n">RED</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">GREEN</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">BLUE</span> <span class="o">=</span> <span class="n">auto</span><span class="p">()</span>
<span class="gp">... </span> <span class="n">MAGENTA</span> <span class="o">=</span> <span class="n">RED</span> <span class="o">|</span> <span class="n">BLUE</span>
<span class="gp">... </span> <span class="n">YELLOW</span> <span class="o">=</span> <span class="n">RED</span> <span class="o">|</span> <span class="n">GREEN</span>
<span class="gp">... </span> <span class="n">CYAN</span> <span class="o">=</span> <span class="n">GREEN</span> <span class="o">|</span> <span class="n">BLUE</span>
<span class="gp">...</span>
<span class="gp">>>> </span><span class="n">Color</span><span class="p">(</span><span class="mi">3</span><span class="p">)</span> <span class="c1"># named combination</span>
<span class="go"><Color.YELLOW: 3></span>
<span class="gp">>>> </span><span class="n">Color</span><span class="p">(</span><span class="mi">7</span><span class="p">)</span> <span class="c1"># not named combination</span>
<span class="go"><Color.CYAN|MAGENTA|BLUE|YELLOW|GREEN|RED: 7></span>
</pre></div>
</div>
</div>
</div>
</div>
</div>
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<h3><a href="../contents.html">Table of Contents</a></h3>
<ul>
<li><a class="reference internal" href="#"><code class="xref py py-mod docutils literal notranslate"><span class="pre">enum</span></code> — Support for enumerations</a><ul>
<li><a class="reference internal" href="#module-contents">Module Contents</a></li>
<li><a class="reference internal" href="#creating-an-enum">Creating an Enum</a></li>
<li><a class="reference internal" href="#programmatic-access-to-enumeration-members-and-their-attributes">Programmatic access to enumeration members and their attributes</a></li>
<li><a class="reference internal" href="#duplicating-enum-members-and-values">Duplicating enum members and values</a></li>
<li><a class="reference internal" href="#ensuring-unique-enumeration-values">Ensuring unique enumeration values</a></li>
<li><a class="reference internal" href="#using-automatic-values">Using automatic values</a></li>
<li><a class="reference internal" href="#iteration">Iteration</a></li>
<li><a class="reference internal" href="#comparisons">Comparisons</a></li>
<li><a class="reference internal" href="#allowed-members-and-attributes-of-enumerations">Allowed members and attributes of enumerations</a></li>
<li><a class="reference internal" href="#restricted-enum-subclassing">Restricted Enum subclassing</a></li>
<li><a class="reference internal" href="#pickling">Pickling</a></li>
<li><a class="reference internal" href="#functional-api">Functional API</a></li>
<li><a class="reference internal" href="#derived-enumerations">Derived Enumerations</a><ul>
<li><a class="reference internal" href="#intenum">IntEnum</a></li>
<li><a class="reference internal" href="#intflag">IntFlag</a></li>
<li><a class="reference internal" href="#flag">Flag</a></li>
<li><a class="reference internal" href="#others">Others</a></li>
</ul>
</li>
<li><a class="reference internal" href="#interesting-examples">Interesting examples</a><ul>
<li><a class="reference internal" href="#omitting-values">Omitting values</a><ul>
<li><a class="reference internal" href="#using-auto">Using <code class="xref py py-class docutils literal notranslate"><span class="pre">auto</span></code></a></li>
<li><a class="reference internal" href="#using-object">Using <code class="xref py py-class docutils literal notranslate"><span class="pre">object</span></code></a></li>
<li><a class="reference internal" href="#using-a-descriptive-string">Using a descriptive string</a></li>
<li><a class="reference internal" href="#using-a-custom-new">Using a custom <code class="xref py py-meth docutils literal notranslate"><span class="pre">__new__()</span></code></a></li>
</ul>
</li>
<li><a class="reference internal" href="#orderedenum">OrderedEnum</a></li>
<li><a class="reference internal" href="#duplicatefreeenum">DuplicateFreeEnum</a></li>
<li><a class="reference internal" href="#planet">Planet</a></li>
<li><a class="reference internal" href="#timeperiod">TimePeriod</a></li>
</ul>
</li>
<li><a class="reference internal" href="#how-are-enums-different">How are Enums different?</a><ul>
<li><a class="reference internal" href="#enum-classes">Enum Classes</a></li>
<li><a class="reference internal" href="#enum-members-aka-instances">Enum Members (aka instances)</a></li>
<li><a class="reference internal" href="#finer-points">Finer Points</a><ul>
<li><a class="reference internal" href="#supported-dunder-names">Supported <code class="docutils literal notranslate"><span class="pre">__dunder__</span></code> names</a></li>
<li><a class="reference internal" href="#supported-sunder-names">Supported <code class="docutils literal notranslate"><span class="pre">_sunder_</span></code> names</a></li>
<li><a class="reference internal" href="#enum-member-type"><code class="docutils literal notranslate"><span class="pre">Enum</span></code> member type</a></li>
<li><a class="reference internal" href="#boolean-value-of-enum-classes-and-members">Boolean value of <code class="docutils literal notranslate"><span class="pre">Enum</span></code> classes and members</a></li>
<li><a class="reference internal" href="#enum-classes-with-methods"><code class="docutils literal notranslate"><span class="pre">Enum</span></code> classes with methods</a></li>
<li><a class="reference internal" href="#combining-members-of-flag">Combining members of <code class="docutils literal notranslate"><span class="pre">Flag</span></code></a></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>
<h4>Previous topic</h4>
<p class="topless"><a href="reprlib.html"
title="previous chapter"><code class="xref py py-mod docutils literal notranslate"><span class="pre">reprlib</span></code> — Alternate <code class="xref py py-func docutils literal notranslate"><span class="pre">repr()</span></code> implementation</a></p>
<h4>Next topic</h4>
<p class="topless"><a href="numeric.html"
title="next chapter">Numeric and Mathematical Modules</a></p>
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