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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"

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<title>8.13. enum — Support for enumerations — Python 3.7.0 說明文件</title>

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<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="本標題的永久連結">¶</a></h1>

3.4 版新加入.

</div>

Source code: <a class="reference external" href="https://github.com/python/cpython/tree/3.7/Lib/enum.py">Lib/enum.py</a>

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.

<h2>8.13.1. Module Contents<a class="headerlink" href="#module-contents" title="本標題的永久連結">¶</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>.

class <code class="descclassname">enum.</code><code class="descname">Enum</code><a class="headerlink" href="#enum.Enum" title="本定義的永久連結">¶</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>

class <code class="descclassname">enum.</code><code class="descname">IntEnum</code><a class="headerlink" href="#enum.IntEnum" title="本定義的永久連結">¶</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>

class <code class="descclassname">enum.</code><code class="descname">IntFlag</code><a class="headerlink" href="#enum.IntFlag" title="本定義的永久連結">¶</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>

class <code class="descclassname">enum.</code><code class="descname">Flag</code><a class="headerlink" href="#enum.Flag" title="本定義的永久連結">¶</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>

<code class="descclassname">enum.</code><code class="descname">unique</code>()<a class="headerlink" href="#enum.unique" title="本定義的永久連結">¶</a></dt>

<dd>Enum class decorator that ensures only one name is bound to any one value.

</dd></dl>

class <code class="descclassname">enum.</code><code class="descname">auto</code><a class="headerlink" href="#enum.auto" title="本定義的永久連結">¶</a></dt>

<dd>Instances are replaced with an appropriate value for Enum members.

</dd></dl>

3.6 版新加入: <code class="docutils literal notranslate">Flag</code>, <code class="docutils literal notranslate">IntFlag</code>, <code class="docutils literal notranslate">auto</code>

</div>

<h2>8.13.2. Creating an Enum<a class="headerlink" href="#creating-an-enum" title="本標題的永久連結">¶</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>>>> from enum import Enum

>>> class Color(Enum):

... RED = 1

... GREEN = 2

... BLUE = 3

...

</pre></div>

</div>

備註

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>

備註

Nomenclature

<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

</ul>

</div>

備註

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>>>> 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>>>> print(repr(Color.RED))

<Color.RED: 1>

</pre></div>

</div>

The type of an enumeration member is the enumeration it belongs to:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> type(Color.RED)

>>> isinstance(Color.GREEN, Color)

True

>>>

</pre></div>

</div>

Enum members also have a property that contains just their item name:

RED

</pre></div>

</div>

Enumerations support iteration, in definition order:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> class Shake(Enum):

... VANILLA = 7

... CHOCOLATE = 4

... COOKIES = 9

... MINT = 3

...

>>> 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>>>> apples = {}

>>> apples[Color.RED] = 'red delicious'

>>> apples[Color.GREEN] = 'granny smith'

>>> apples == {Color.RED: 'red delicious', Color.GREEN: 'granny smith'}

True

</pre></div>

</div>

<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="本標題的永久連結">¶</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>>>> Color(1)

<Color.RED: 1>

>>> Color(3)

<Color.BLUE: 3>

</pre></div>

</div>

If you want to access enum members by name, use item access:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> Color['RED']

<Color.RED: 1>

>>> Color['GREEN']

<Color.GREEN: 2>

</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>>>> member = Color.RED

>>> member.name

'RED'

>>> member.value

1

</pre></div>

</div>

<h2>8.13.4. Duplicating enum members and values<a class="headerlink" href="#duplicating-enum-members-and-values" title="本標題的永久連結">¶</a></h2>

Having two enum members with the same name is invalid:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> class Shape(Enum):

... SQUARE = 2

... SQUARE = 3

...

Traceback (most recent call last):

...

TypeError: Attempted to reuse key: 'SQUARE'

</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>>>> class Shape(Enum):

... SQUARE = 2

... DIAMOND = 1

... CIRCLE = 3

... ALIAS_FOR_SQUARE = 2

...

>>> Shape.SQUARE

<Shape.SQUARE: 2>

>>> Shape.ALIAS_FOR_SQUARE

<Shape.SQUARE: 2>

>>> Shape(2)

<Shape.SQUARE: 2>

</pre></div>

</div>

備註

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>

<h2>8.13.5. Ensuring unique enumeration values<a class="headerlink" href="#ensuring-unique-enumeration-values" title="本標題的永久連結">¶</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:

<dt>

<code class="descclassname">@</code><code class="descclassname">enum.</code><code class="descname">unique</code></dt>

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:

>>> @unique

... class Mistake(Enum):

... ONE = 1

... TWO = 2

... THREE = 3

... FOUR = 3

...

Traceback (most recent call last):

...

ValueError: duplicate values found in <enum 'Mistake'>: FOUR -> THREE

</pre></div>

</div>

<h2>8.13.6. Using automatic values<a class="headerlink" href="#using-automatic-values" title="本標題的永久連結">¶</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>:

>>> class Color(Enum):

... RED = auto()

... BLUE = auto()

... GREEN = auto()

...

>>> list(Color)

[<Color.RED: 1>, <Color.BLUE: 2>, <Color.GREEN: 3>]

</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>>>> class AutoName(Enum):

... def _generate_next_value_(name, start, count, last_values):

... return name

...

>>> class Ordinal(AutoName):

... NORTH = auto()

... SOUTH = auto()

... EAST = auto()

... WEST = auto()

...

>>> list(Ordinal)

[<Ordinal.NORTH: 'NORTH'>, <Ordinal.SOUTH: 'SOUTH'>, <Ordinal.EAST: 'EAST'>, <Ordinal.WEST: 'WEST'>]

</pre></div>

</div>

備註

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>

<h2>8.13.7. Iteration<a class="headerlink" href="#iteration" title="本標題的永久連結">¶</a></h2>

Iterating over the members of an enum does not provide the aliases:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> list(Shape)

[<Shape.SQUARE: 2>, <Shape.DIAMOND: 1>, <Shape.CIRCLE: 3>]

</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>>>> for name, member in Shape.__members__.items():

... name, member

...

('SQUARE', <Shape.SQUARE: 2>)

('DIAMOND', <Shape.DIAMOND: 1>)

('CIRCLE', <Shape.CIRCLE: 3>)

('ALIAS_FOR_SQUARE', <Shape.SQUARE: 2>)

</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>>>> [name for name, member in Shape.__members__.items() if member.name != name]

['ALIAS_FOR_SQUARE']

</pre></div>

</div>

<h2>8.13.8. Comparisons<a class="headerlink" href="#comparisons" title="本標題的永久連結">¶</a></h2>

Enumeration members are compared by identity:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> Color.RED is Color.RED

True

>>> Color.RED is Color.BLUE

False

>>> 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>>>> Color.RED < Color.BLUE

Traceback (most recent call last):

File "<stdin>", line 1, in <module>

TypeError: '<' not supported between instances of 'Color' and 'Color'

</pre></div>

</div>

Equality comparisons are defined though:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> Color.BLUE == Color.RED

False

>>> Color.BLUE != Color.RED

True

>>> 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>>>> Color.BLUE == 2

False

</pre></div>

</div>

<h2>8.13.9. Allowed members and attributes of enumerations<a class="headerlink" href="#allowed-members-and-attributes-of-enumerations" title="本標題的永久連結">¶</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>>>> class Mood(Enum):

... FUNKY = 1

... HAPPY = 3

...

... def describe(self):

... # self is the member here

... return self.name, self.value

...

... def __str__(self):

... return 'my custom str! {0}'.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>>>> Mood.favorite_mood()

<Mood.HAPPY: 3>

>>> Mood.HAPPY.describe()

('HAPPY', 3)

>>> str(Mood.FUNKY)

'my custom str! 1'

</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.), descriptors (methods are also descriptors), and

variable names listed in <code class="xref py py-attr docutils literal notranslate">_ignore_</code>.

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>

<h2>8.13.10. Restricted subclassing of enumerations<a class="headerlink" href="#restricted-subclassing-of-enumerations" title="本標題的永久連結">¶</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>>>> 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>>>> class Foo(Enum):

... def some_behavior(self):

... pass

...

>>> 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>

<h2>8.13.11. Pickling<a class="headerlink" href="#pickling" title="本標題的永久連結">¶</a></h2>

Enumerations can be pickled and unpickled:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> from test.test_enum import Fruit

>>> from pickle import dumps, loads

>>> 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.

備註

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>

<h2>8.13.12. Functional API<a class="headerlink" href="#functional-api" title="本標題的永久連結">¶</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>>>> Animal = Enum('Animal', 'ANT BEE CAT DOG')

>>> Animal

>>> Animal.ANT

<Animal.ANT: 1>

>>> Animal.ANT.value

1

>>> list(Animal)

[<Animal.ANT: 1>, <Animal.BEE: 2>, <Animal.CAT: 3>, <Animal.DOG: 4>]

</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>>>> 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:

</pre></div>

</div>

警告

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:

</pre></div>

</div>

The complete signature is:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>Enum(value='NewEnumName', names=<...>, *, module='...', qualname='...', type=<mixed-in class>, start=1)

</pre></div>

</div>

<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>'RED GREEN BLUE' | 'RED,GREEN,BLUE' | 'RED, GREEN, BLUE'

</pre></div>

</div>

or an iterator of names:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>['RED', 'GREEN', 'BLUE']

</pre></div>

</div>

or an iterator of (name, value) pairs:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>[('CYAN', 4), ('MAGENTA', 5), ('YELLOW', 6)]

</pre></div>

</div>

or a mapping:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>{'CHARTREUSE': 7, 'SEA_GREEN': 11, 'ROSEMARY': 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>

3.5 版更變: The start parameter was added.

</div>

<h2>8.13.13. Derived Enumerations<a class="headerlink" href="#derived-enumerations" title="本標題的永久連結">¶</a></h2>

<h3>8.13.13.1. IntEnum<a class="headerlink" href="#intenum" title="本標題的永久連結">¶</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:

>>> class Shape(IntEnum):

... CIRCLE = 1

... SQUARE = 2

...

>>> class Request(IntEnum):

... POST = 1

... GET = 2

...

>>> Shape == 1

False

>>> Shape.CIRCLE == 1

True

>>> 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>>>> class Shape(IntEnum):

... CIRCLE = 1

... SQUARE = 2

...

>>> class Color(Enum):

... RED = 1

... GREEN = 2

...

>>> 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>>>> int(Shape.CIRCLE)

1

>>> ['a', 'b', 'c'][Shape.CIRCLE]

'b'

>>> [i for i in range(Shape.SQUARE)]

[0, 1]

</pre></div>

</div>

<h3>8.13.13.2. IntFlag<a class="headerlink" href="#intflag" title="本標題的永久連結">¶</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 (&, |, ^, ~) 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.

3.6 版新加入.

</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:

>>> class Perm(IntFlag):

... R = 4

... W = 2

... X = 1

...

>>> Perm.R | Perm.W

<Perm.R|W: 6>

>>> Perm.R + Perm.W

6

>>> RW = Perm.R | Perm.W

>>> 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>>>> class Perm(IntFlag):

... R = 4

... W = 2

... X = 1

... RWX = 7

>>> Perm.RWX

<Perm.RWX: 7>

>>> ~Perm.RWX

<Perm.-8: -8>

</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>>>> Perm.R & Perm.X

<Perm.0: 0>

>>> bool(Perm.R & 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>>>> Perm.X | 8

<Perm.8|X: 9>

</pre></div>

</div>

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 (&, |, ^, ~). Unlike

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.

3.6 版新加入.

</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>:

>>> class Color(Flag):

... RED = auto()

... BLUE = auto()

... GREEN = auto()

...

>>> Color.RED & Color.GREEN

<Color.0: 0>

>>> bool(Color.RED & 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>>>> class Color(Flag):

... RED = auto()

... BLUE = auto()

... GREEN = auto()

... WHITE = RED | BLUE | GREEN

...

>>> Color.WHITE

<Color.WHITE: 7>

</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>>>> class Color(Flag):

... BLACK = 0

... RED = auto()

... BLUE = auto()

... GREEN = auto()

...

>>> Color.BLACK

<Color.BLACK: 0>

>>> bool(Color.BLACK)

False

</pre></div>

</div>

備註

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>

<h3>8.13.13.4. Others<a class="headerlink" href="#others" title="本標題的永久連結">¶</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:

<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.

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

<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>

<h2>8.13.14. Interesting examples<a class="headerlink" href="#interesting-examples" title="本標題的永久連結">¶</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.

<h3>8.13.14.1. Omitting values<a class="headerlink" href="#omitting-values" title="本標題的永久連結">¶</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:

<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>>>> class NoValue(Enum):

... def __repr__(self):

... return '<%s.%s>' % (self.__class__.__name__, self.name)

...

</pre></div>

</div>

<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="本標題的永久連結">¶</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>>>> class Color(NoValue):

... RED = auto()

... BLUE = auto()

... GREEN = auto()

...

>>> Color.GREEN

<Color.GREEN>

</pre></div>

</div>

<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="本標題的永久連結">¶</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>>>> class Color(NoValue):

... RED = object()

... GREEN = object()

... BLUE = object()

...

>>> Color.GREEN

<Color.GREEN>

</pre></div>

</div>

<h4>8.13.14.1.3. Using a descriptive string<a class="headerlink" href="#using-a-descriptive-string" title="本標題的永久連結">¶</a></h4>

Using a string as the value would look like:

<div class="highlight-python3 notranslate"><div class="highlight"><pre>>>> class Color(NoValue):

... RED = 'stop'

... GREEN = 'go'

... BLUE = 'too fast!'

...

>>> Color.GREEN

<Color.GREEN>

>>> Color.GREEN.value

'go'

</pre></div>

</div>

<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="本標題的永久連結">¶</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>>>> class AutoNumber(NoValue):

... def __new__(cls):

... value = len(cls.__members__) + 1

... obj = object.__new__(cls)

... obj._value_ = value

... return obj

...

>>> class Color(AutoNumber):

... RED = ()

... GREEN = ()

... BLUE = ()

...

>>> Color.GREEN

<Color.GREEN>

>>> Color.GREEN.value

2

</pre></div>

</div>

備註

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>

<h3>8.13.14.2. OrderedEnum<a class="headerlink" href="#orderedenum" title="本標題的永久連結">¶</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>>>> class OrderedEnum(Enum):

... def __ge__(self, other):

... if self.__class__ is other.__class__:

... return self.value >= other.value

... return NotImplemented

... def __gt__(self, other):

... return self.value > other.value

... return NotImplemented

... def __le__(self, other):

... return self.value <= other.value

... return NotImplemented

... def __lt__(self, other):

... return self.value < other.value

... return NotImplemented

...

>>> class Grade(OrderedEnum):

... A = 5

... B = 4

... C = 3

... D = 2

... F = 1

...

>>> Grade.C < Grade.A

True

</pre></div>

</div>

<h3>8.13.14.3. DuplicateFreeEnum<a class="headerlink" href="#duplicatefreeenum" title="本標題的永久連結">¶</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>>>> 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(

... "aliases not allowed in DuplicateFreeEnum: %r --> %r"

... % (a, e))

...

>>> class Color(DuplicateFreeEnum):

... RED = 1

... GREEN = 2

... BLUE = 3

... GRENE = 2

...

Traceback (most recent call last):

...

ValueError: aliases not allowed in DuplicateFreeEnum: 'GRENE' --> 'GREEN'

</pre></div>

</div>

備註

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>

<h3>8.13.14.4. Planet<a class="headerlink" href="#planet" title="本標題的永久連結">¶</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>>>> 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

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