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 <div class="section" id="module-enum">
<h1>8.13. <a class="reference internal" href="#module-enum" title="enum: Implementation of an enumeration class."><code class="xref py py-mod docutils literal notranslate">enum</code></a> — Support for enumerations<a class="headerlink" href="#module-enum" title="Permalink to this headline">¶</a></h1>
<div class="versionadded">
New in version 3.4.
</div>
Source code: <a class="reference external" href="https://github.com/python/cpython/tree/3.6/Lib/enum.py">Lib/enum.py</a>
<hr class="docutils" />
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.
<div class="section" id="module-contents">
<h2>8.13.1. Module Contents<a class="headerlink" href="#module-contents" title="Permalink to this headline">¶</a></h2>
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">Enum</code></a>, <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate">IntEnum</code></a>, <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate">Flag</code></a>, and
<a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</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">unique()</code></a>, and one
helper, <a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate">auto</code></a>.
<dl class="class">
<dt id="enum.Enum">
class <code class="descclassname">enum.</code><code class="descname">Enum</code><a class="headerlink" href="#enum.Enum" title="Permalink to this definition">¶</a></dt>
<dd>Base class for creating enumerated constants. See section
<a class="reference internal" href="#functional-api">Functional API</a> for an alternate construction syntax.
</dd></dl>

<dl class="class">
<dt id="enum.IntEnum">
class <code class="descclassname">enum.</code><code class="descname">IntEnum</code><a class="headerlink" href="#enum.IntEnum" title="Permalink to this definition">¶</a></dt>
<dd>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">int</code></a>.
</dd></dl>

<dl class="class">
<dt id="enum.IntFlag">
class <code class="descclassname">enum.</code><code class="descname">IntFlag</code><a class="headerlink" href="#enum.IntFlag" title="Permalink to this definition">¶</a></dt>
<dd>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">IntFlag</code></a> membership.
<a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</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">int</code></a>.
</dd></dl>

<dl class="class">
<dt id="enum.Flag">
class <code class="descclassname">enum.</code><code class="descname">Flag</code><a class="headerlink" href="#enum.Flag" title="Permalink to this definition">¶</a></dt>
<dd>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">Flag</code></a> membership.
</dd></dl>

<dl class="function">
<dt id="enum.unique">
<code class="descclassname">enum.</code><code class="descname">unique</code>()<a class="headerlink" href="#enum.unique" title="Permalink to this definition">¶</a></dt>
<dd>Enum class decorator that ensures only one name is bound to any one value.
</dd></dl>

<dl class="class">
<dt id="enum.auto">
class <code class="descclassname">enum.</code><code class="descname">auto</code><a class="headerlink" href="#enum.auto" title="Permalink to this definition">¶</a></dt>
<dd>Instances are replaced with an appropriate value for Enum members.
</dd></dl>

<div class="versionadded">
New in version 3.6: <code class="docutils literal notranslate">Flag</code>, <code class="docutils literal notranslate">IntFlag</code>, <code class="docutils literal notranslate">auto</code>
</div>
</div>
<div class="section" id="creating-an-enum">
<h2>8.13.2. Creating an Enum<a class="headerlink" href="#creating-an-enum" title="Permalink to this headline">¶</a></h2>
Enumerations are created using the <a class="reference internal" href="../reference/compound_stmts.html#class"><code class="xref std std-keyword docutils literal notranslate">class</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">Enum</code></a> as
follows:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from enum import Enum
&gt;&gt;&gt; class Color(Enum):
... RED = 1
... GREEN = 2
... BLUE = 3
...
</pre></div>
</div>
<div class="admonition note">
Note
Enum member values
Member values can be anything: <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a>, <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</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">auto</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">auto</code></a> with other values.
</div>
<div class="admonition note">
Note
Nomenclature
<ul class="last simple">
<li>The class <code class="xref py py-class docutils literal notranslate">Color</code> is an enumeration (or enum)</li>
<li>The attributes <code class="xref py py-attr docutils literal notranslate">Color.RED</code>, <code class="xref py py-attr docutils literal notranslate">Color.GREEN</code>, etc., are
enumeration members (or enum members) and are functionally constants.</li>
<li>The enum members have names and values (the name of
<code class="xref py py-attr docutils literal notranslate">Color.RED</code> is <code class="docutils literal notranslate">RED</code>, the value of <code class="xref py py-attr docutils literal notranslate">Color.BLUE</code> is
<code class="docutils literal notranslate">3</code>, etc.)</li>
</ul>
</div>
<div class="admonition note">
Note
Even though we use the <a class="reference internal" href="../reference/compound_stmts.html#class"><code class="xref std std-keyword docutils literal notranslate">class</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.
</div>
Enumeration members have human readable string representations:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; print(Color.RED)
Color.RED
</pre></div>
</div>
…while their <code class="docutils literal notranslate">repr</code> has more information:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; print(repr(Color.RED))
&lt;Color.RED: 1&gt;
</pre></div>
</div>
The type of an enumeration member is the enumeration it belongs to:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; type(Color.RED)
&lt;enum &#39;Color&#39;&gt;
&gt;&gt;&gt; isinstance(Color.GREEN, Color)
True
&gt;&gt;&gt;
</pre></div>
</div>
Enum members also have a property that contains just their item name:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; print(Color.RED.name)
RED
</pre></div>
</div>
Enumerations support iteration, in definition order:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Shake(Enum):
... VANILLA = 7
... CHOCOLATE = 4
... COOKIES = 9
... MINT = 3
...
&gt;&gt;&gt; for shake in Shake:
... print(shake)
...
Shake.VANILLA
Shake.CHOCOLATE
Shake.COOKIES
Shake.MINT
</pre></div>
</div>
Enumeration members are hashable, so they can be used in dictionaries and sets:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; apples = {}
&gt;&gt;&gt; apples[Color.RED] = &#39;red delicious&#39;
&gt;&gt;&gt; apples[Color.GREEN] = &#39;granny smith&#39;
&gt;&gt;&gt; apples == {Color.RED: &#39;red delicious&#39;, Color.GREEN: &#39;granny smith&#39;}
True
</pre></div>
</div>
</div>
<div class="section" id="programmatic-access-to-enumeration-members-and-their-attributes">
<h2>8.13.3. 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>
Sometimes it’s useful to access members in enumerations programmatically (i.e.
situations where <code class="docutils literal notranslate">Color.RED</code> won’t do because the exact color is not known
at program-writing time). <code class="docutils literal notranslate">Enum</code> allows such access:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Color(1)
&lt;Color.RED: 1&gt;
&gt;&gt;&gt; Color(3)
&lt;Color.BLUE: 3&gt;
</pre></div>
</div>
If you want to access enum members by name, use item access:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Color[&#39;RED&#39;]
&lt;Color.RED: 1&gt;
&gt;&gt;&gt; Color[&#39;GREEN&#39;]
&lt;Color.GREEN: 2&gt;
</pre></div>
</div>
If you have an enum member and need its <code class="xref py py-attr docutils literal notranslate">name</code> or <code class="xref py py-attr docutils literal notranslate">value</code>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; member = Color.RED
&gt;&gt;&gt; member.name
&#39;RED&#39;
&gt;&gt;&gt; member.value
1
</pre></div>
</div>
</div>
<div class="section" id="duplicating-enum-members-and-values">
<h2>8.13.4. Duplicating enum members and values<a class="headerlink" href="#duplicating-enum-members-and-values" title="Permalink to this headline">¶</a></h2>
Having two enum members with the same name is invalid:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Shape(Enum):
... SQUARE = 2
... SQUARE = 3
...
Traceback (most recent call last):
...
TypeError: Attempted to reuse key: &#39;SQUARE&#39;
</pre></div>
</div>
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:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Shape(Enum):
... SQUARE = 2
... DIAMOND = 1
... CIRCLE = 3
... ALIAS_FOR_SQUARE = 2
...
&gt;&gt;&gt; Shape.SQUARE
&lt;Shape.SQUARE: 2&gt;
&gt;&gt;&gt; Shape.ALIAS_FOR_SQUARE
&lt;Shape.SQUARE: 2&gt;
&gt;&gt;&gt; Shape(2)
&lt;Shape.SQUARE: 2&gt;
</pre></div>
</div>
<div class="admonition note">
Note
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.
</div>
</div>
<div class="section" id="ensuring-unique-enumeration-values">
<h2>8.13.5. Ensuring unique enumeration values<a class="headerlink" href="#ensuring-unique-enumeration-values" title="Permalink to this headline">¶</a></h2>
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:
<dl class="function">
<dt>
<code class="descclassname">&#64;</code><code class="descclassname">enum.</code><code class="descname">unique</code></dt>
<dd></dd></dl>

A <a class="reference internal" href="../reference/compound_stmts.html#class"><code class="xref std std-keyword docutils literal notranslate">class</code></a> decorator specifically for enumerations. It searches an
enumeration’s <code class="xref py py-attr docutils literal notranslate">__members__</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">ValueError</code></a> is raised with the details:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from enum import Enum, unique
&gt;&gt;&gt; @unique
... class Mistake(Enum):
... ONE = 1
... TWO = 2
... THREE = 3
... FOUR = 3
...
Traceback (most recent call last):
...
ValueError: duplicate values found in &lt;enum &#39;Mistake&#39;&gt;: FOUR -&gt; THREE
</pre></div>
</div>
</div>
<div class="section" id="using-automatic-values">
<h2>8.13.6. Using automatic values<a class="headerlink" href="#using-automatic-values" title="Permalink to this headline">¶</a></h2>
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">auto</code></a>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from enum import Enum, auto
&gt;&gt;&gt; class Color(Enum):
... RED = auto()
... BLUE = auto()
... GREEN = auto()
...
&gt;&gt;&gt; list(Color)
[&lt;Color.RED: 1&gt;, &lt;Color.BLUE: 2&gt;, &lt;Color.GREEN: 3&gt;]
</pre></div>
</div>
The values are chosen by <code class="xref py py-func docutils literal notranslate">_generate_next_value_()</code>, which can be
overridden:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class AutoName(Enum):
... def _generate_next_value_(name, start, count, last_values):
... return name
...
&gt;&gt;&gt; class Ordinal(AutoName):
... NORTH = auto()
... SOUTH = auto()
... EAST = auto()
... WEST = auto()
...
&gt;&gt;&gt; list(Ordinal)
[&lt;Ordinal.NORTH: &#39;NORTH&#39;&gt;, &lt;Ordinal.SOUTH: &#39;SOUTH&#39;&gt;, &lt;Ordinal.EAST: &#39;EAST&#39;&gt;, &lt;Ordinal.WEST: &#39;WEST&#39;&gt;]
</pre></div>
</div>
<div class="admonition note">
Note
The goal of the default <code class="xref py py-meth docutils literal notranslate">_generate_next_value_()</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">int</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">int</code></a> provided, but
the way it does this is an implementation detail and may change.
</div>
</div>
<div class="section" id="iteration">
<h2>8.13.7. Iteration<a class="headerlink" href="#iteration" title="Permalink to this headline">¶</a></h2>
Iterating over the members of an enum does not provide the aliases:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; list(Shape)
[&lt;Shape.SQUARE: 2&gt;, &lt;Shape.DIAMOND: 1&gt;, &lt;Shape.CIRCLE: 3&gt;]
</pre></div>
</div>
The special attribute <code class="docutils literal notranslate">__members__</code> is an ordered dictionary mapping names
to members. It includes all names defined in the enumeration, including the
aliases:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; for name, member in Shape.__members__.items():
... name, member
...
(&#39;SQUARE&#39;, &lt;Shape.SQUARE: 2&gt;)
(&#39;DIAMOND&#39;, &lt;Shape.DIAMOND: 1&gt;)
(&#39;CIRCLE&#39;, &lt;Shape.CIRCLE: 3&gt;)
(&#39;ALIAS_FOR_SQUARE&#39;, &lt;Shape.SQUARE: 2&gt;)
</pre></div>
</div>
The <code class="docutils literal notranslate">__members__</code> attribute can be used for detailed programmatic access to
the enumeration members. For example, finding all the aliases:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; [name for name, member in Shape.__members__.items() if member.name != name]
[&#39;ALIAS_FOR_SQUARE&#39;]
</pre></div>
</div>
</div>
<div class="section" id="comparisons">
<h2>8.13.8. Comparisons<a class="headerlink" href="#comparisons" title="Permalink to this headline">¶</a></h2>
Enumeration members are compared by identity:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Color.RED is Color.RED
True
&gt;&gt;&gt; Color.RED is Color.BLUE
False
&gt;&gt;&gt; Color.RED is not Color.BLUE
True
</pre></div>
</div>
Ordered comparisons between enumeration values are not supported. Enum
members are not integers (but see <a class="reference internal" href="#intenum">IntEnum</a> below):
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Color.RED &lt; Color.BLUE
Traceback (most recent call last):
 File &quot;&lt;stdin&gt;&quot;, line 1, in &lt;module&gt;
TypeError: &#39;&lt;&#39; not supported between instances of &#39;Color&#39; and &#39;Color&#39;
</pre></div>
</div>
Equality comparisons are defined though:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Color.BLUE == Color.RED
False
&gt;&gt;&gt; Color.BLUE != Color.RED
True
&gt;&gt;&gt; Color.BLUE == Color.BLUE
True
</pre></div>
</div>
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">IntEnum</code></a> was explicitly designed to behave differently, see
below):
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Color.BLUE == 2
False
</pre></div>
</div>
</div>
<div class="section" id="allowed-members-and-attributes-of-enumerations">
<h2>8.13.9. Allowed members and attributes of enumerations<a class="headerlink" href="#allowed-members-and-attributes-of-enumerations" title="Permalink to this headline">¶</a></h2>
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 is important,
enumerations can have arbitrary values.
Enumerations are Python classes, and can have methods and special methods as
usual. If we have this enumeration:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Mood(Enum):
... FUNKY = 1
... HAPPY = 3
...
... def describe(self):
... # self is the member here
... return self.name, self.value
...
... def __str__(self):
... return &#39;my custom str! {0}&#39;.format(self.value)
...
... @classmethod
... def favorite_mood(cls):
... # cls here is the enumeration
... return cls.HAPPY
...
</pre></div>
</div>
Then:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Mood.favorite_mood()
&lt;Mood.HAPPY: 3&gt;
&gt;&gt;&gt; Mood.HAPPY.describe()
(&#39;HAPPY&#39;, 3)
&gt;&gt;&gt; str(Mood.FUNKY)
&#39;my custom str! 1&#39;
</pre></div>
</div>
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">__str__()</code></a>,
<a class="reference internal" href="../reference/datamodel.html#object.__add__" title="object.__add__"><code class="xref py py-meth docutils literal notranslate">__add__()</code></a>, etc.) and descriptors (methods are also descriptors).
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">__new__()</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">__init__()</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.
</div>
<div class="section" id="restricted-subclassing-of-enumerations">
<h2>8.13.10. Restricted subclassing of enumerations<a class="headerlink" href="#restricted-subclassing-of-enumerations" title="Permalink to this headline">¶</a></h2>
Subclassing an enumeration is allowed only if the enumeration does not define
any members. So this is forbidden:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class MoreColor(Color):
... PINK = 17
...
Traceback (most recent call last):
...
TypeError: Cannot extend enumerations
</pre></div>
</div>
But this is allowed:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Foo(Enum):
... def some_behavior(self):
... pass
...
&gt;&gt;&gt; class Bar(Foo):
... HAPPY = 1
... SAD = 2
...
</pre></div>
</div>
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.)
</div>
<div class="section" id="pickling">
<h2>8.13.11. Pickling<a class="headerlink" href="#pickling" title="Permalink to this headline">¶</a></h2>
Enumerations can be pickled and unpickled:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from test.test_enum import Fruit
&gt;&gt;&gt; from pickle import dumps, loads
&gt;&gt;&gt; Fruit.TOMATO is loads(dumps(Fruit.TOMATO))
True
</pre></div>
</div>
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.
<div class="admonition note">
Note
With pickle protocol version 4 it is possible to easily pickle enums
nested in other classes.
</div>
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">__reduce_ex__()</code></a> in the enumeration class.
</div>
<div class="section" id="functional-api">
<h2>8.13.12. Functional API<a class="headerlink" href="#functional-api" title="Permalink to this headline">¶</a></h2>
The <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</code></a> class is callable, providing the following functional API:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Animal = Enum(&#39;Animal&#39;, &#39;ANT BEE CAT DOG&#39;)
&gt;&gt;&gt; Animal
&lt;enum &#39;Animal&#39;&gt;
&gt;&gt;&gt; Animal.ANT
&lt;Animal.ANT: 1&gt;
&gt;&gt;&gt; Animal.ANT.value
1
&gt;&gt;&gt; list(Animal)
[&lt;Animal.ANT: 1&gt;, &lt;Animal.BEE: 2&gt;, &lt;Animal.CAT: 3&gt;, &lt;Animal.DOG: 4&gt;]
</pre></div>
</div>
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">namedtuple</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">Enum</code></a> is the name of the enumeration.
The second argument is the source 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">start</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">Enum</code></a> is returned. In other words, the above
assignment to <code class="xref py py-class docutils literal notranslate">Animal</code> is equivalent to:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Animal(Enum):
... ANT = 1
... BEE = 2
... CAT = 3
... DOG = 4
...
</pre></div>
</div>
The reason for defaulting to <code class="docutils literal notranslate">1</code> as the starting number and not <code class="docutils literal notranslate">0</code> is
that <code class="docutils literal notranslate">0</code> is <code class="docutils literal notranslate">False</code> in a boolean sense, but enum members all evaluate
to <code class="docutils literal notranslate">True</code>.
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:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Animal = Enum(&#39;Animal&#39;, &#39;ANT BEE CAT DOG&#39;, module=__name__)
</pre></div>
</div>
<div class="admonition warning">
Warning
If <code class="docutils literal notranslate">module</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.
</div>
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">__qualname__</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:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Animal = Enum(&#39;Animal&#39;, &#39;ANT BEE CAT DOG&#39;, qualname=&#39;SomeData.Animal&#39;)
</pre></div>
</div>
The complete signature is:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>Enum(value=&#39;NewEnumName&#39;, names=&lt;...&gt;, *, module=&#39;...&#39;, qualname=&#39;...&#39;, type=&lt;mixed-in class&gt;, start=1)
</pre></div>
</div>
<table class="docutils field-list" frame="void" rules="none">
<col class="field-name" />
<col class="field-body" />
<tbody valign="top">
<tr class="field-odd field"><th class="field-name">value:</th><td class="field-body">What the new Enum class will record as its name.
</td>
</tr>
<tr class="field-even field"><th class="field-name">names:</th><td class="field-body">The Enum members. This can be a whitespace or comma separated string
(values will start at 1 unless otherwise specified):
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&#39;RED GREEN BLUE&#39; | &#39;RED,GREEN,BLUE&#39; | &#39;RED, GREEN, BLUE&#39;
</pre></div>
</div>
or an iterator of names:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>[&#39;RED&#39;, &#39;GREEN&#39;, &#39;BLUE&#39;]
</pre></div>
</div>
or an iterator of (name, value) pairs:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>[(&#39;CYAN&#39;, 4), (&#39;MAGENTA&#39;, 5), (&#39;YELLOW&#39;, 6)]
</pre></div>
</div>
or a mapping:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>{&#39;CHARTREUSE&#39;: 7, &#39;SEA_GREEN&#39;: 11, &#39;ROSEMARY&#39;: 42}
</pre></div>
</div>
</td>
</tr>
<tr class="field-odd field"><th class="field-name">module:</th><td class="field-body">name of module where new Enum class can be found.
</td>
</tr>
<tr class="field-even field"><th class="field-name">qualname:</th><td class="field-body">where in module new Enum class can be found.
</td>
</tr>
<tr class="field-odd field"><th class="field-name">type:</th><td class="field-body">type to mix in to new Enum class.
</td>
</tr>
<tr class="field-even field"><th class="field-name">start:</th><td class="field-body">number to start counting at if only names are passed in.
</td>
</tr>
</tbody>
</table>
<div class="versionchanged">
Changed in version 3.5: The start parameter was added.
</div>
</div>
<div class="section" id="derived-enumerations">
<h2>8.13.13. Derived Enumerations<a class="headerlink" href="#derived-enumerations" title="Permalink to this headline">¶</a></h2>
<div class="section" id="intenum">
<h3>8.13.13.1. IntEnum<a class="headerlink" href="#intenum" title="Permalink to this headline">¶</a></h3>
The first variation of <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</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">int</code></a>. Members of an <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate">IntEnum</code></a> can be compared to integers;
by extension, integer enumerations of different types can also be compared
to each other:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from enum import IntEnum
&gt;&gt;&gt; class Shape(IntEnum):
... CIRCLE = 1
... SQUARE = 2
...
&gt;&gt;&gt; class Request(IntEnum):
... POST = 1
... GET = 2
...
&gt;&gt;&gt; Shape == 1
False
&gt;&gt;&gt; Shape.CIRCLE == 1
True
&gt;&gt;&gt; Shape.CIRCLE == Request.POST
True
</pre></div>
</div>
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">Enum</code></a> enumerations:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Shape(IntEnum):
... CIRCLE = 1
... SQUARE = 2
...
&gt;&gt;&gt; class Color(Enum):
... RED = 1
... GREEN = 2
...
&gt;&gt;&gt; Shape.CIRCLE == Color.RED
False
</pre></div>
</div>
<a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate">IntEnum</code></a> values behave like integers in other ways you’d expect:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; int(Shape.CIRCLE)
1
&gt;&gt;&gt; [&#39;a&#39;, &#39;b&#39;, &#39;c&#39;][Shape.CIRCLE]
&#39;b&#39;
&gt;&gt;&gt; [i for i in range(Shape.SQUARE)]
[0, 1]
</pre></div>
</div>
</div>
<div class="section" id="intflag">
<h3>8.13.13.2. IntFlag<a class="headerlink" href="#intflag" title="Permalink to this headline">¶</a></h3>
The next variation of <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</code></a> provided, <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</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">int</code></a>. The difference being <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</code></a> members can be combined
using the bitwise operators (&amp;, |, ^, ~) 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">IntFlag</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">IntFlag</code></a>
members also subclass <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</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">int</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">IntFlag</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">IntFlag</code></a> membership.
<div class="versionadded">
New in version 3.6.
</div>
Sample <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</code></a> class:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from enum import IntFlag
&gt;&gt;&gt; class Perm(IntFlag):
... R = 4
... W = 2
... X = 1
...
&gt;&gt;&gt; Perm.R | Perm.W
&lt;Perm.R|W: 6&gt;
&gt;&gt;&gt; Perm.R + Perm.W
6
&gt;&gt;&gt; RW = Perm.R | Perm.W
&gt;&gt;&gt; Perm.R in RW
True
</pre></div>
</div>
It is also possible to name the combinations:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Perm(IntFlag):
... R = 4
... W = 2
... X = 1
... RWX = 7
&gt;&gt;&gt; Perm.RWX
&lt;Perm.RWX: 7&gt;
&gt;&gt;&gt; ~Perm.RWX
&lt;Perm.-8: -8&gt;
</pre></div>
</div>
Another important difference between <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</code></a> and <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</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">False</code></a>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Perm.R &amp; Perm.X
&lt;Perm.0: 0&gt;
&gt;&gt;&gt; bool(Perm.R &amp; Perm.X)
False
</pre></div>
</div>
Because <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</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">int</code></a> they can
be combined with them:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; Perm.X | 8
&lt;Perm.8|X: 9&gt;
</pre></div>
</div>
</div>
<div class="section" id="flag">
<h3>8.13.13.3. Flag<a class="headerlink" href="#flag" title="Permalink to this headline">¶</a></h3>
The last variation is <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate">Flag</code></a>. Like <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</code></a>, <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate">Flag</code></a>
members can be combined using the bitwise operators (&amp;, |, ^, ~). Unlike
<a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</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">Flag</code></a> enumeration, nor <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</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">auto</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">Flag</code></a> select an appropriate value.
<div class="versionadded">
New in version 3.6.
</div>
Like <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</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">Flag</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">False</code></a>:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; from enum import Flag, auto
&gt;&gt;&gt; class Color(Flag):
... RED = auto()
... BLUE = auto()
... GREEN = auto()
...
&gt;&gt;&gt; Color.RED &amp; Color.GREEN
&lt;Color.0: 0&gt;
&gt;&gt;&gt; bool(Color.RED &amp; Color.GREEN)
False
</pre></div>
</div>
Individual flags should have values that are powers of two (1, 2, 4, 8, …),
while combinations of flags won’t:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Color(Flag):
... RED = auto()
... BLUE = auto()
... GREEN = auto()
... WHITE = RED | BLUE | GREEN
...
&gt;&gt;&gt; Color.WHITE
&lt;Color.WHITE: 7&gt;
</pre></div>
</div>
Giving a name to the “no flags set” condition does not change its boolean
value:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Color(Flag):
... BLACK = 0
... RED = auto()
... BLUE = auto()
... GREEN = auto()
...
&gt;&gt;&gt; Color.BLACK
&lt;Color.BLACK: 0&gt;
&gt;&gt;&gt; bool(Color.BLACK)
False
</pre></div>
</div>
<div class="admonition note">
Note
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">Enum</code></a> and <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate">Flag</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">IntEnum</code></a> and <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</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">IntEnum</code></a>
and <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</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">Enum</code></a> and
<a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate">Flag</code></a> will not do; for example, when integer constants are replaced
with enumerations, or for interoperability with other systems.
</div>
</div>
<div class="section" id="others">
<h3>8.13.13.4. Others<a class="headerlink" href="#others" title="Permalink to this headline">¶</a></h3>
While <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate">IntEnum</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">enum</code></a> module, it would be very
simple to implement independently:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>class IntEnum(int, Enum):
 pass
</pre></div>
</div>
This demonstrates how similar derived enumerations can be defined; for example
a <code class="xref py py-class docutils literal notranslate">StrEnum</code> that mixes in <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a> instead of <a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a>.
Some rules:
<ol class="arabic simple">
<li>When subclassing <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</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">Enum</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">IntEnum</code></a>
example above.</li>
<li>While <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</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">int</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">int</code></a> or
<a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</code></a>.</li>
<li>When another data type is mixed in, the <code class="xref py py-attr docutils literal notranslate">value</code> attribute is not the
same as the enum member itself, although it is equivalent and will compare
equal.</li>
<li>%-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">Enum</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">__str__()</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">__repr__()</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.</li>
<li><a class="reference internal" href="../reference/lexical_analysis.html#f-strings">Formatted string literals</a>, <a class="reference internal" href="stdtypes.html#str.format" title="str.format"><code class="xref py py-meth docutils literal notranslate">str.format()</code></a>,
and <a class="reference internal" href="functions.html#format" title="format"><code class="xref py py-func docutils literal notranslate">format()</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">__format__()</code></a>. If the <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</code></a> class’s <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-func docutils literal notranslate">str()</code></a> or
<a class="reference internal" href="functions.html#repr" title="repr"><code class="xref py py-func docutils literal notranslate">repr()</code></a> is desired, use the <cite>!s</cite> or <cite>!r</cite> format codes.</li>
</ol>
</div>
</div>
<div class="section" id="interesting-examples">
<h2>8.13.14. Interesting examples<a class="headerlink" href="#interesting-examples" title="Permalink to this headline">¶</a></h2>
While <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</code></a>, <a class="reference internal" href="#enum.IntEnum" title="enum.IntEnum"><code class="xref py py-class docutils literal notranslate">IntEnum</code></a>, <a class="reference internal" href="#enum.IntFlag" title="enum.IntFlag"><code class="xref py py-class docutils literal notranslate">IntFlag</code></a>, and <a class="reference internal" href="#enum.Flag" title="enum.Flag"><code class="xref py py-class docutils literal notranslate">Flag</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.
<div class="section" id="omitting-values">
<h3>8.13.14.1. Omitting values<a class="headerlink" href="#omitting-values" title="Permalink to this headline">¶</a></h3>
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:
<ul class="simple">
<li>use instances of <a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate">auto</code></a> for the value</li>
<li>use instances of <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> as the value</li>
<li>use a descriptive string as the value</li>
<li>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">__new__()</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">int</code></a> value</li>
</ul>
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.
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">repr()</code></a> that also hides
the (unimportant) value:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class NoValue(Enum):
... def __repr__(self):
... return &#39;&lt;%s.%s&gt;&#39; % (self.__class__.__name__, self.name)
...
</pre></div>
</div>
<div class="section" id="using-auto">
<h4>8.13.14.1.1. Using <a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate">auto</code></a><a class="headerlink" href="#using-auto" title="Permalink to this headline">¶</a></h4>
Using <a class="reference internal" href="#enum.auto" title="enum.auto"><code class="xref py py-class docutils literal notranslate">auto</code></a> would look like:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Color(NoValue):
... RED = auto()
... BLUE = auto()
... GREEN = auto()
...
&gt;&gt;&gt; Color.GREEN
&lt;Color.GREEN&gt;
</pre></div>
</div>
</div>
<div class="section" id="using-object">
<h4>8.13.14.1.2. Using <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a><a class="headerlink" href="#using-object" title="Permalink to this headline">¶</a></h4>
Using <a class="reference internal" href="functions.html#object" title="object"><code class="xref py py-class docutils literal notranslate">object</code></a> would look like:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Color(NoValue):
... RED = object()
... GREEN = object()
... BLUE = object()
...
&gt;&gt;&gt; Color.GREEN
&lt;Color.GREEN&gt;
</pre></div>
</div>
</div>
<div class="section" id="using-a-descriptive-string">
<h4>8.13.14.1.3. Using a descriptive string<a class="headerlink" href="#using-a-descriptive-string" title="Permalink to this headline">¶</a></h4>
Using a string as the value would look like:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Color(NoValue):
... RED = &#39;stop&#39;
... GREEN = &#39;go&#39;
... BLUE = &#39;too fast!&#39;
...
&gt;&gt;&gt; Color.GREEN
&lt;Color.GREEN&gt;
&gt;&gt;&gt; Color.GREEN.value
&#39;go&#39;
</pre></div>
</div>
</div>
<div class="section" id="using-a-custom-new">
<h4>8.13.14.1.4. 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">__new__()</code></a><a class="headerlink" href="#using-a-custom-new" title="Permalink to this headline">¶</a></h4>
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">__new__()</code></a> would look like:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class AutoNumber(NoValue):
... def __new__(cls):
... value = len(cls.__members__) + 1
... obj = object.__new__(cls)
... obj._value_ = value
... return obj
...
&gt;&gt;&gt; class Color(AutoNumber):
... RED = ()
... GREEN = ()
... BLUE = ()
...
&gt;&gt;&gt; Color.GREEN
&lt;Color.GREEN&gt;
&gt;&gt;&gt; Color.GREEN.value
2
</pre></div>
</div>
<div class="admonition note">
Note
The <a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</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">__new__()</code></a> which is used after
class creation for lookup of existing members.
</div>
</div>
</div>
<div class="section" id="orderedenum">
<h3>8.13.14.2. OrderedEnum<a class="headerlink" href="#orderedenum" title="Permalink to this headline">¶</a></h3>
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">IntEnum</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">Enum</code></a> invariants (such as not being comparable to other
enumerations):
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class OrderedEnum(Enum):
... def __ge__(self, other):
... if self.__class__ is other.__class__:
... return self.value &gt;= other.value
... return NotImplemented
... def __gt__(self, other):
... if self.__class__ is other.__class__:
... return self.value &gt; other.value
... return NotImplemented
... def __le__(self, other):
... if self.__class__ is other.__class__:
... return self.value &lt;= other.value
... return NotImplemented
... def __lt__(self, other):
... if self.__class__ is other.__class__:
... return self.value &lt; other.value
... return NotImplemented
...
&gt;&gt;&gt; class Grade(OrderedEnum):
... A = 5
... B = 4
... C = 3
... D = 2
... F = 1
...
&gt;&gt;&gt; Grade.C &lt; Grade.A
True
</pre></div>
</div>
</div>
<div class="section" id="duplicatefreeenum">
<h3>8.13.14.3. DuplicateFreeEnum<a class="headerlink" href="#duplicatefreeenum" title="Permalink to this headline">¶</a></h3>
Raises an error if a duplicate member name is found instead of creating an
alias:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class DuplicateFreeEnum(Enum):
... def __init__(self, *args):
... cls = self.__class__
... if any(self.value == e.value for e in cls):
... a = self.name
... e = cls(self.value).name
... raise ValueError(
... &quot;aliases not allowed in DuplicateFreeEnum: %r --&gt; %r&quot;
... % (a, e))
...
&gt;&gt;&gt; class Color(DuplicateFreeEnum):
... RED = 1
... GREEN = 2
... BLUE = 3
... GRENE = 2
...
Traceback (most recent call last):
...
ValueError: aliases not allowed in DuplicateFreeEnum: &#39;GRENE&#39; --&gt; &#39;GREEN&#39;
</pre></div>
</div>
<div class="admonition note">
Note
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">unique()</code></a> decorator can be used instead.
</div>
</div>
<div class="section" id="planet">
<h3>8.13.14.4. Planet<a class="headerlink" href="#planet" title="Permalink to this headline">¶</a></h3>
If <a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</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">__init__()</code></a> is defined the value of the enum member
will be passed to those methods:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Planet(Enum):
... MERCURY = (3.303e+23, 2.4397e6)
... VENUS = (4.869e+24, 6.0518e6)
... EARTH = (5.976e+24, 6.37814e6)
... MARS = (6.421e+23, 3.3972e6)
... JUPITER = (1.9e+27, 7.1492e7)
... SATURN = (5.688e+26, 6.0268e7)
... URANUS = (8.686e+25, 2.5559e7)
... NEPTUNE = (1.024e+26, 2.4746e7)
... def __init__(self, mass, radius):
... self.mass = mass # in kilograms
... self.radius = radius # in meters
... @property
... def surface_gravity(self):
... # universal gravitational constant (m3 kg-1 s-2)
... G = 6.67300E-11
... return G * self.mass / (self.radius * self.radius)
...
&gt;&gt;&gt; Planet.EARTH.value
(5.976e+24, 6378140.0)
&gt;&gt;&gt; Planet.EARTH.surface_gravity
9.802652743337129
</pre></div>
</div>
</div>
</div>
<div class="section" id="how-are-enums-different">
<h2>8.13.15. How are Enums different?<a class="headerlink" href="#how-are-enums-different" title="Permalink to this headline">¶</a></h2>
Enums have a custom metaclass that affects many aspects of both derived Enum
classes and their instances (members).
<div class="section" id="enum-classes">
<h3>8.13.15.1. Enum Classes<a class="headerlink" href="#enum-classes" title="Permalink to this headline">¶</a></h3>
The <code class="xref py py-class docutils literal notranslate">EnumMeta</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">__contains__()</code></a>, <a class="reference internal" href="../reference/datamodel.html#object.__dir__" title="object.__dir__"><code class="xref py py-meth docutils literal notranslate">__dir__()</code></a>, <a class="reference internal" href="../reference/datamodel.html#object.__iter__" title="object.__iter__"><code class="xref py py-meth docutils literal notranslate">__iter__()</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">Enum</code></a> class that fail on a typical
class, such as <cite>list(Color)</cite> or <cite>some_var in Color</cite>. <code class="xref py py-class docutils literal notranslate">EnumMeta</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">Enum</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">__new__()</code></a>, <a class="reference internal" href="pickle.html#object.__getnewargs__" title="object.__getnewargs__"><code class="xref py py-meth docutils literal notranslate">__getnewargs__()</code></a>,
<a class="reference internal" href="../reference/datamodel.html#object.__str__" title="object.__str__"><code class="xref py py-meth docutils literal notranslate">__str__()</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">__repr__()</code></a>).
</div>
<div class="section" id="enum-members-aka-instances">
<h3>8.13.15.2. Enum Members (aka instances)<a class="headerlink" href="#enum-members-aka-instances" title="Permalink to this headline">¶</a></h3>
The most interesting thing about Enum members is that they are singletons.
<code class="xref py py-class docutils literal notranslate">EnumMeta</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">Enum</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">__new__()</code></a> in place to ensure
that no new ones are ever instantiated by returning only the existing
member instances.
</div>
<div class="section" id="finer-points">
<h3>8.13.15.3. Finer Points<a class="headerlink" href="#finer-points" title="Permalink to this headline">¶</a></h3>
<div class="section" id="supported-dunder-names">
<h4>8.13.15.3.1. Supported <code class="docutils literal notranslate">__dunder__</code> names<a class="headerlink" href="#supported-dunder-names" title="Permalink to this headline">¶</a></h4>
<code class="xref py py-attr docutils literal notranslate">__members__</code> is an <code class="xref py py-class docutils literal notranslate">OrderedDict</code> of <code class="docutils literal notranslate">member_name</code>:<code class="docutils literal notranslate">member</code>
items. It is only available on the class.
<a class="reference internal" href="../reference/datamodel.html#object.__new__" title="object.__new__"><code class="xref py py-meth docutils literal notranslate">__new__()</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">_value_</code> appropriately. Once
all the members are created it is no longer used.
</div>
<div class="section" id="supported-sunder-names">
<h4>8.13.15.3.2. Supported <code class="docutils literal notranslate">_sunder_</code> names<a class="headerlink" href="#supported-sunder-names" title="Permalink to this headline">¶</a></h4>
<ul class="simple">
<li><code class="docutils literal notranslate">_name_</code> – name of the member</li>
<li><code class="docutils literal notranslate">_value_</code> – value of the member; can be set / modified in <code class="docutils literal notranslate">__new__</code></li>
<li><code class="docutils literal notranslate">_missing_</code> – a lookup function used when a value is not found; may be
overridden</li>
<li><code class="docutils literal notranslate">_order_</code> – used in Python 2/3 code to ensure member order is consistent
(class attribute, removed during class creation)</li>
<li><code class="docutils literal notranslate">_generate_next_value_</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">auto</code></a> to get an appropriate value for an enum member; may be
overridden</li>
</ul>
<div class="versionadded">
New in version 3.6: <code class="docutils literal notranslate">_missing_</code>, <code class="docutils literal notranslate">_order_</code>, <code class="docutils literal notranslate">_generate_next_value_</code>
</div>
To help keep Python 2 / Python 3 code in sync an <code class="xref py py-attr docutils literal notranslate">_order_</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:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Color(Enum):
... _order_ = &#39;RED GREEN BLUE&#39;
... RED = 1
... BLUE = 3
... GREEN = 2
...
Traceback (most recent call last):
...
TypeError: member order does not match _order_
</pre></div>
</div>
<div class="admonition note">
Note
In Python 2 code the <code class="xref py py-attr docutils literal notranslate">_order_</code> attribute is necessary as definition
order is lost before it can be recorded.
</div>
</div>
<div class="section" id="enum-member-type">
<h4>8.13.15.3.3. <code class="docutils literal notranslate">Enum</code> member type<a class="headerlink" href="#enum-member-type" title="Permalink to this headline">¶</a></h4>
<a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</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">Enum</code></a> class, and are
normally accessed as <code class="docutils literal notranslate">EnumClass.member</code>. Under certain circumstances they
can also be accessed as <code class="docutils literal notranslate">EnumClass.member.member</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">Enum</code></a> member you are looking for (this is another good reason to use
all-uppercase names for members):
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class FieldTypes(Enum):
... name = 0
... value = 1
... size = 2
...
&gt;&gt;&gt; FieldTypes.value.size
&lt;FieldTypes.size: 2&gt;
&gt;&gt;&gt; FieldTypes.size.value
2
</pre></div>
</div>
<div class="versionchanged">
Changed in version 3.5.
</div>
</div>
<div class="section" id="boolean-value-of-enum-classes-and-members">
<h4>8.13.15.3.4. Boolean value of <code class="docutils literal notranslate">Enum</code> classes and members<a class="headerlink" href="#boolean-value-of-enum-classes-and-members" title="Permalink to this headline">¶</a></h4>
<a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</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">Enum</code></a> types (such as
<a class="reference internal" href="functions.html#int" title="int"><code class="xref py py-class docutils literal notranslate">int</code></a>, <a class="reference internal" href="stdtypes.html#str" title="str"><code class="xref py py-class docutils literal notranslate">str</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">True</code></a>. To make your
own Enum’s boolean evaluation depend on the member’s value add the following to
your class:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>def __bool__(self):
 return bool(self.value)
</pre></div>
</div>
<a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</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">True</code></a>.
</div>
<div class="section" id="enum-classes-with-methods">
<h4>8.13.15.3.5. <code class="docutils literal notranslate">Enum</code> classes with methods<a class="headerlink" href="#enum-classes-with-methods" title="Permalink to this headline">¶</a></h4>
If you give your <a class="reference internal" href="#enum.Enum" title="enum.Enum"><code class="xref py py-class docutils literal notranslate">Enum</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">dir()</code></a> of the member,
but not of the class:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; dir(Planet)
[&#39;EARTH&#39;, &#39;JUPITER&#39;, &#39;MARS&#39;, &#39;MERCURY&#39;, &#39;NEPTUNE&#39;, &#39;SATURN&#39;, &#39;URANUS&#39;, &#39;VENUS&#39;, &#39;__class__&#39;, &#39;__doc__&#39;, &#39;__members__&#39;, &#39;__module__&#39;]
&gt;&gt;&gt; dir(Planet.EARTH)
[&#39;__class__&#39;, &#39;__doc__&#39;, &#39;__module__&#39;, &#39;name&#39;, &#39;surface_gravity&#39;, &#39;value&#39;]
</pre></div>
</div>
</div>
<div class="section" id="combining-members-of-flag">
<h4>8.13.15.3.6. Combining members of <code class="docutils literal notranslate">Flag</code><a class="headerlink" href="#combining-members-of-flag" title="Permalink to this headline">¶</a></h4>
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">repr()</code></a> will include
all named flags and all named combinations of flags that are in the value:
<div class="highlight-python3 notranslate"><div class="highlight"><pre>&gt;&gt;&gt; class Color(Flag):
... RED = auto()
... GREEN = auto()
... BLUE = auto()
... MAGENTA = RED | BLUE
... YELLOW = RED | GREEN
... CYAN = GREEN | BLUE
...
&gt;&gt;&gt; Color(3) # named combination
&lt;Color.YELLOW: 3&gt;
&gt;&gt;&gt; Color(7) # not named combination
&lt;Color.CYAN|MAGENTA|BLUE|YELLOW|GREEN|RED: 7&gt;
</pre></div>
</div>
</div>
</div>
</div>
</div>

</div>
 </div>
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 <div class="sphinxsidebar" role="navigation" aria-label="main navigation">
 <div class="sphinxsidebarwrapper">
 <h3><a href="../contents.html">Table Of Contents</a></h3>
 <ul>
<li><a class="reference internal" href="#">8.13. <code class="docutils literal notranslate">enum</code> — Support for enumerations</a><ul>
<li><a class="reference internal" href="#module-contents">8.13.1. Module Contents</a></li>
<li><a class="reference internal" href="#creating-an-enum">8.13.2. Creating an Enum</a></li>
<li><a class="reference internal" href="#programmatic-access-to-enumeration-members-and-their-attributes">8.13.3. Programmatic access to enumeration members and their attributes</a></li>
<li><a class="reference internal" href="#duplicating-enum-members-and-values">8.13.4. Duplicating enum members and values</a></li>
<li><a class="reference internal" href="#ensuring-unique-enumeration-values">8.13.5. Ensuring unique enumeration values</a></li>
<li><a class="reference internal" href="#using-automatic-values">8.13.6. Using automatic values</a></li>
<li><a class="reference internal" href="#iteration">8.13.7. Iteration</a></li>
<li><a class="reference internal" href="#comparisons">8.13.8. Comparisons</a></li>
<li><a class="reference internal" href="#allowed-members-and-attributes-of-enumerations">8.13.9. Allowed members and attributes of enumerations</a></li>
<li><a class="reference internal" href="#restricted-subclassing-of-enumerations">8.13.10. Restricted subclassing of enumerations</a></li>
<li><a class="reference internal" href="#pickling">8.13.11. Pickling</a></li>
<li><a class="reference internal" href="#functional-api">8.13.12. Functional API</a></li>
<li><a class="reference internal" href="#derived-enumerations">8.13.13. Derived Enumerations</a><ul>
<li><a class="reference internal" href="#intenum">8.13.13.1. IntEnum</a></li>
<li><a class="reference internal" href="#intflag">8.13.13.2. IntFlag</a></li>
<li><a class="reference internal" href="#flag">8.13.13.3. Flag</a></li>
<li><a class="reference internal" href="#others">8.13.13.4. Others</a></li>
</ul>
</li>
<li><a class="reference internal" href="#interesting-examples">8.13.14. Interesting examples</a><ul>
<li><a class="reference internal" href="#omitting-values">8.13.14.1. Omitting values</a><ul>
<li><a class="reference internal" href="#using-auto">8.13.14.1.1. Using <code class="docutils literal notranslate">auto</code></a></li>
<li><a class="reference internal" href="#using-object">8.13.14.1.2. Using <code class="docutils literal notranslate">object</code></a></li>
<li><a class="reference internal" href="#using-a-descriptive-string">8.13.14.1.3. Using a descriptive string</a></li>
<li><a class="reference internal" href="#using-a-custom-new">8.13.14.1.4. Using a custom <code class="docutils literal notranslate">__new__()</code></a></li>
</ul>
</li>
<li><a class="reference internal" href="#orderedenum">8.13.14.2. OrderedEnum</a></li>
<li><a class="reference internal" href="#duplicatefreeenum">8.13.14.3. DuplicateFreeEnum</a></li>
<li><a class="reference internal" href="#planet">8.13.14.4. Planet</a></li>
</ul>
</li>
<li><a class="reference internal" href="#how-are-enums-different">8.13.15. How are Enums different?</a><ul>
<li><a class="reference internal" href="#enum-classes">8.13.15.1. Enum Classes</a></li>
<li><a class="reference internal" href="#enum-members-aka-instances">8.13.15.2. Enum Members (aka instances)</a></li>
<li><a class="reference internal" href="#finer-points">8.13.15.3. Finer Points</a><ul>
<li><a class="reference internal" href="#supported-dunder-names">8.13.15.3.1. Supported <code class="docutils literal notranslate">__dunder__</code> names</a></li>
<li><a class="reference internal" href="#supported-sunder-names">8.13.15.3.2. Supported <code class="docutils literal notranslate">_sunder_</code> names</a></li>
<li><a class="reference internal" href="#enum-member-type">8.13.15.3.3. <code class="docutils literal notranslate">Enum</code> member type</a></li>
<li><a class="reference internal" href="#boolean-value-of-enum-classes-and-members">8.13.15.3.4. Boolean value of <code class="docutils literal notranslate">Enum</code> classes and members</a></li>
<li><a class="reference internal" href="#enum-classes-with-methods">8.13.15.3.5. <code class="docutils literal notranslate">Enum</code> classes with methods</a></li>
<li><a class="reference internal" href="#combining-members-of-flag">8.13.15.3.6. Combining members of <code class="docutils literal notranslate">Flag</code></a></li>
</ul>
</li>
</ul>
</li>
</ul>
</li>
</ul>

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 title="previous chapter">8.12. <code class="docutils literal notranslate">reprlib</code> — Alternate <code class="docutils literal notranslate">repr()</code> implementation</a>
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