enum — 支持枚举 ¶

3.4 版新增。

源代码： Lib/enum.py

---

枚举是绑定到唯一常量值的一组符号名称 (成员)。在枚举中，成员可以通过身份进行比较，且枚举本身还可以迭代。

注意

枚举成员案例

因为枚举用于表示常量，所以推荐枚举成员使用 UPPER_CASE (大写) 名称，且将在以下范例中使用该样式。

模块内容 ¶

此模块定义了可以用于定义名称和值的唯一集的 4 个枚举类: Enum , IntEnum , Flag ，和 IntFlag 。它还定义了一个装饰器 unique() ，和一个帮手 auto .

class 枚举。 Enum ¶

用于创建枚举常量的基类。见章节 函数式 API 了解替代构造句法。

class 枚举。 IntEnum ¶

Base class for creating enumerated constants that are also subclasses of int .

class 枚举。 IntFlag ¶

Base class for creating enumerated constants that can be combined using the bitwise operators without losing their IntFlag 成员资格。 IntFlag 成员也是子类的 int .

class 枚举。 Flag ¶

Base class for creating enumerated constants that can be combined using the bitwise operations without losing their Flag 成员资格。

枚举。 unique ( )

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

class 枚举。 auto ¶

Instances are replaced with an appropriate value for Enum members. Initial value starts at 1.

3.6 版新增： Flag , IntFlag , auto

创建枚举 ¶

枚举的创建是使用 class syntax, which makes them easy to read and write. An alternative creation method is described in 函数式 API 。要定义枚举，子类 Enum 如下：

>>> from enum import Enum
>>> class Color(Enum):
...     RED = 1
...     GREEN = 2
...     BLUE = 3
...
						

注意

枚举成员值

成员值可以是任何值： int , str , etc.. If the exact value is unimportant you may use auto instances and an appropriate value will be chosen for you. Care must be taken if you mix auto with other values.

注意

Nomenclature

• 类 Color 是 enumeration (或 enum )

• 属性 Color.RED , Color.GREEN ，等，是 enumeration 成员 (或 enum 成员 ) 且功能上均是常量。

• 枚举成员拥有 名称 and 值 (名称对于 Color.RED is RED ，值对于 Color.BLUE is 3 ，等)

注意

即使使用 class 句法能创建 Enum, 但 Enum 不是正常 Python 类。见 枚举有什么不同？ 了解更多细节。

enumeration 成员拥有人类可读的字符串表示：

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

… 而它们的 repr 拥有更多信息：

>>> print(repr(Color.RED))
<Color.RED: 1>
						

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

>>> type(Color.RED)
<enum 'Color'>
>>> isinstance(Color.GREEN, Color)
True
>>>
						

枚举成员还有恰好包含其项名称的特性：

>>> print(Color.RED.name)
RED
						

枚举支持迭代，按定义次序：

>>> 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
						

枚举成员可哈希，因此它们可用于字典和集：

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

编程方式访问枚举成员及其属性 ¶

Sometimes it’s useful to access members in enumerations programmatically (i.e. situations where Color.RED won’t do because the exact color is not known at program-writing time). Enum allows such access:

>>> Color(1)
<Color.RED: 1>
>>> Color(3)
<Color.BLUE: 3>
						

若想要访问枚举成员通过 name ，使用项访问：

>>> Color['RED']
<Color.RED: 1>
>>> Color['GREEN']
<Color.GREEN: 2>
						

若有枚举成员且需要其 name or value :

>>> member = Color.RED
>>> member.name
'RED'
>>> member.value
1
						

复制枚举成员和值 ¶

拥有 2 同名成员的枚举是无效的：

>>> class Shape(Enum):
...     SQUARE = 2
...     SQUARE = 3
...
Traceback (most recent call last):
...
TypeError: Attempted to reuse key: 'SQUARE'
						

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:

>>> 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>
						

注意

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.

确保唯一枚举值 ¶

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:

@ 枚举。 unique ¶

A class decorator specifically for enumerations. It searches an enumeration’s __members__ gathering any aliases it finds; if any are found ValueError is raised with the details:

>>> from enum import Enum, unique
>>> @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
					

使用自动值 ¶

若确切值不重要，可以使用 auto :

>>> from enum import Enum, auto
>>> class Color(Enum):
...     RED = auto()
...     BLUE = auto()
...     GREEN = auto()
...
>>> list(Color)
[<Color.RED: 1>, <Color.BLUE: 2>, <Color.GREEN: 3>]
					

The values are chosen by _generate_next_value_() , which can be overridden:

>>> 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'>]
					

注意

The goal of the default _generate_next_value_() method is to provide the next int in sequence with the last int provided, but the way it does this is an implementation detail and may change.

注意

The _generate_next_value_() method must be defined before any members.

迭代 ¶

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

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

The special attribute __members__ is a read-only ordered mapping of names to members. It includes all names defined in the enumeration, including the aliases:

>>> 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>)
					

The __members__ attribute can be used for detailed programmatic access to the enumeration members. For example, finding all the aliases:

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

比较 ¶

Enumeration members are compared by identity:

>>> Color.RED is Color.RED
True
>>> Color.RED is Color.BLUE
False
>>> Color.RED is not Color.BLUE
True
					

Ordered comparisons between enumeration values are not supported. Enum members are not integers (but see IntEnum below):

>>> Color.RED < Color.BLUE
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '<' not supported between instances of 'Color' and 'Color'
					

Equality comparisons are defined though:

>>> Color.BLUE == Color.RED
False
>>> Color.BLUE != Color.RED
True
>>> Color.BLUE == Color.BLUE
True
					

Comparisons against non-enumeration values will always compare not equal (again, IntEnum was explicitly designed to behave differently, see below):

>>> Color.BLUE == 2
False
					

允许枚举成员和属性 ¶

The examples above use integers for enumeration values. Using integers is short and handy (and provided by default by the 函数式 API ), 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:

>>> 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
...
					

Then:

>>> Mood.favorite_mood()
<Mood.HAPPY: 3>
>>> Mood.HAPPY.describe()
('HAPPY', 3)
>>> str(Mood.FUNKY)
'my custom str! 1'
					

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 ( __str__() , __add__() , etc.), descriptors (methods are also descriptors), and variable names listed in _ignore_ .

Note: if your enumeration defines __new__() and/or __init__() then whatever value(s) were given to the enum member will be passed into those methods. See Planet 范例。

限定枚举子类化 ¶

新的 Enum class must have one base Enum class, up to one concrete data type, and as many object -based mixin classes as needed. The order of these base classes is:

class EnumName([mix-in, ...,] [data-type,] base-enum):
    pass
					

Also, subclassing an enumeration is allowed only if the enumeration does not define any members. So this is forbidden:

>>> class MoreColor(Color):
...     PINK = 17
...
Traceback (most recent call last):
...
TypeError: Cannot extend enumerations
					

But this is allowed:

>>> class Foo(Enum):
...     def some_behavior(self):
...         pass
...
>>> class Bar(Foo):
...     HAPPY = 1
...     SAD = 2
...
					

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 OrderedEnum for an example.)

腌制 ¶

Enumerations can be pickled and unpickled:

>>> from test.test_enum import Fruit
>>> from pickle import dumps, loads
>>> Fruit.TOMATO is loads(dumps(Fruit.TOMATO))
True
					

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.

注意

With pickle protocol version 4 it is possible to easily pickle enums nested in other classes.

It is possible to modify how Enum members are pickled/unpickled by defining __reduce_ex__() in the enumeration class.

函数式 API ¶

The Enum 类可调用，提供以下 API 功能：

>>> Animal = Enum('Animal', 'ANT BEE CAT DOG')
>>> Animal
<enum 'Animal'>
>>> Animal.ANT
<Animal.ANT: 1>
>>> Animal.ANT.value
1
>>> list(Animal)
[<Animal.ANT: 1>, <Animal.BEE: 2>, <Animal.CAT: 3>, <Animal.DOG: 4>]
					

The semantics of this API resemble namedtuple . The first argument of the call to Enum 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 start parameter to specify a different starting value). A new class derived from Enum is returned. In other words, the above assignment to Animal 相当于：

>>> class Animal(Enum):
...     ANT = 1
...     BEE = 2
...     CAT = 3
...     DOG = 4
...
					

The reason for defaulting to 1 as the starting number and not 0 is that 0 is False in a boolean sense, but enum members all evaluate to True .

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:

>>> Animal = Enum('Animal', 'ANT BEE CAT DOG', module=__name__)
					

警告

若 module 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.

The new pickle protocol 4 also, in some circumstances, relies on __qualname__ 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:

>>> Animal = Enum('Animal', 'ANT BEE CAT DOG', qualname='SomeData.Animal')
					

The complete signature is:

Enum(value='NewEnumName', names=<...>, *, module='...', qualname='...', type=<mixed-in class>, start=1)
					

值

What the new Enum class will record as its name.

名称

The Enum members. This can be a whitespace or comma separated string (values will start at 1 unless otherwise specified):

'RED GREEN BLUE' | 'RED,GREEN,BLUE' | 'RED, GREEN, BLUE'
						

或名称迭代器：

['RED', 'GREEN', 'BLUE']
						

或 (name, value) 对迭代器：

[('CYAN', 4), ('MAGENTA', 5), ('YELLOW', 6)]
						

或映射：

{'CHARTREUSE': 7, 'SEA_GREEN': 11, 'ROSEMARY': 42}
						

模块

name of module where new Enum class can be found.

qualname

where in module new Enum class can be found.

type

能混入新 Enum 类的类型。

start

number to start counting at if only names are passed in.

3.5 版改变： The start 参数被添加。

派生枚举 ¶

IntEnum ¶

The first variation of Enum that is provided is also a subclass of int . Members of an IntEnum can be compared to integers; by extension, integer enumerations of different types can also be compared to each other:

>>> from enum import IntEnum
>>> 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
						

However, they still can’t be compared to standard Enum 枚举：

>>> class Shape(IntEnum):
...     CIRCLE = 1
...     SQUARE = 2
...
>>> class Color(Enum):
...     RED = 1
...     GREEN = 2
...
>>> Shape.CIRCLE == Color.RED
False
						

IntEnum values behave like integers in other ways you’d expect:

>>> int(Shape.CIRCLE)
1
>>> ['a', 'b', 'c'][Shape.CIRCLE]
'b'
>>> [i for i in range(Shape.SQUARE)]
[0, 1]
						

IntFlag ¶

The next variation of Enum provided, IntFlag , is also based on int . The difference being IntFlag members can be combined using the bitwise operators (&, |, ^, ~) and the result is still an IntFlag member. However, as the name implies, IntFlag members also subclass int and can be used wherever an int is used. Any operation on an IntFlag member besides the bit-wise operations will lose the IntFlag 成员资格。

3.6 版新增。

样本 IntFlag 类：

>>> from enum import IntFlag
>>> 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
						

It is also possible to name the combinations:

>>> class Perm(IntFlag):
...     R = 4
...     W = 2
...     X = 1
...     RWX = 7
>>> Perm.RWX
<Perm.RWX: 7>
>>> ~Perm.RWX
<Perm.-8: -8>
						

Another important difference between IntFlag and Enum is that if no flags are set (the value is 0), its boolean evaluation is False :

>>> Perm.R & Perm.X
<Perm.0: 0>
>>> bool(Perm.R & Perm.X)
False
						

因为 IntFlag 成员也是子类的 int 可以将它们组合在一起：

>>> Perm.X | 8
<Perm.8|X: 9>
						

标志 ¶

最后变体是 Flag 。像 IntFlag , Flag members can be combined using the bitwise operators (&, |, ^, ~). Unlike IntFlag , they cannot be combined with, nor compared against, any other Flag enumeration, nor int . While it is possible to specify the values directly it is recommended to use auto as the value and let Flag select an appropriate value.

3.6 版新增。

像 IntFlag , if a combination of Flag members results in no flags being set, the boolean evaluation is False :

>>> from enum import Flag, auto
>>> class Color(Flag):
...     RED = auto()
...     BLUE = auto()
...     GREEN = auto()
...
>>> Color.RED & Color.GREEN
<Color.0: 0>
>>> bool(Color.RED & Color.GREEN)
False
						

Individual flags should have values that are powers of two (1, 2, 4, 8, …), while combinations of flags won’t:

>>> class Color(Flag):
...     RED = auto()
...     BLUE = auto()
...     GREEN = auto()
...     WHITE = RED | BLUE | GREEN
...
>>> Color.WHITE
<Color.WHITE: 7>
						

Giving a name to the “no flags set” condition does not change its boolean value:

>>> class Color(Flag):
...     BLACK = 0
...     RED = auto()
...     BLUE = auto()
...     GREEN = auto()
...
>>> Color.BLACK
<Color.BLACK: 0>
>>> bool(Color.BLACK)
False
						

注意

对于大多数新代码， Enum and Flag are strongly recommended, since IntEnum and IntFlag break some semantic promises of an enumeration (by being comparable to integers, and thus by transitivity to other unrelated enumerations). IntEnum and IntFlag should be used only in cases where Enum and Flag will not do; for example, when integer constants are replaced with enumerations, or for interoperability with other systems.

其它 ¶

While IntEnum 属于 enum module, it would be very simple to implement independently:

class IntEnum(int, Enum):
    pass
						

This demonstrates how similar derived enumerations can be defined; for example a StrEnum that mixes in str 而不是 int .

一些规则：

1. 当子类化 Enum , mix-in types must appear before Enum itself in the sequence of bases, as in the IntEnum example above.

2. While Enum can have members of any type, once you mix in an additional type, all the members must have values of that type, e.g. int above. This restriction does not apply to mix-ins which only add methods and don’t specify another data type such as int or str .

3. When another data type is mixed in, the value 属性为 not the same as the enum member itself, although it is equivalent and will compare equal.

4. %-style formatting: %s and %r call the Enum 类的 __str__() and __repr__() respectively; other codes (such as %i or %h for IntEnum) treat the enum member as its mixed-in type.

5. 格式化字符串文字 , str.format() ，和 format() will use the mixed-in type’s __format__() unless __str__() or __format__() is overridden in the subclass, in which case the overridden methods or Enum methods will be used. Use the !s and !r format codes to force usage of the Enum 类的 __str__() and __repr__() 方法。

当要使用 __new__() vs. __init__() ¶

__new__() must be used whenever you want to customize the actual value of the Enum member. Any other modifications may go in either __new__() or __init__() ，采用 __init__() being preferred.

For example, if you want to pass several items to the constructor, but only want one of them to be the value:

>>> class Coordinate(bytes, Enum):
...     """
...     Coordinate with binary codes that can be indexed by the int code.
...     """
...     def __new__(cls, value, label, unit):
...         obj = bytes.__new__(cls, [value])
...         obj._value_ = value
...         obj.label = label
...         obj.unit = unit
...         return obj
...     PX = (0, 'P.X', 'km')
...     PY = (1, 'P.Y', 'km')
...     VX = (2, 'V.X', 'km/s')
...     VY = (3, 'V.Y', 'km/s')
...
>>> print(Coordinate['PY'])
Coordinate.PY
>>> print(Coordinate(3))
Coordinate.VY
					

有趣范例 ¶

While Enum , IntEnum , IntFlag ，和 Flag 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.

省略值 ¶

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:

• 使用实例化的 auto 对于值

• 使用实例化的 object 作为值

• use a descriptive string as the value

• use a tuple as the value and a custom __new__() to replace the tuple with an int 值

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 repr() that also hides the (unimportant) value:

>>> class NoValue(Enum):
...     def __repr__(self):
...         return '<%s.%s>' % (self.__class__.__name__, self.name)
...
					

使用 auto ¶

使用 auto 将看起来像：

>>> class Color(NoValue):
...     RED = auto()
...     BLUE = auto()
...     GREEN = auto()
...
>>> Color.GREEN
<Color.GREEN>
					

使用 object ¶

使用 object 将看起来像：

>>> class Color(NoValue):
...     RED = object()
...     GREEN = object()
...     BLUE = object()
...
>>> Color.GREEN
<Color.GREEN>
					

使用描述性字符串 ¶

使用字符串作为值将看起来像：

>>> class Color(NoValue):
...     RED = 'stop'
...     GREEN = 'go'
...     BLUE = 'too fast!'
...
>>> Color.GREEN
<Color.GREEN>
>>> Color.GREEN.value
'go'
					

使用自定义 __new__() ¶

使用自动编号 __new__() 将看起来像：

>>> 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
					

To make a more general purpose AutoNumber ，添加 *args 到签名：

>>> class AutoNumber(NoValue):
...     def __new__(cls, *args):      # this is the only change from above
...         value = len(cls.__members__) + 1
...         obj = object.__new__(cls)
...         obj._value_ = value
...         return obj
...
					

Then when you inherit from AutoNumber you can write your own __init__ to handle any extra arguments:

>>> class Swatch(AutoNumber):
...     def __init__(self, pantone='unknown'):
...         self.pantone = pantone
...     AUBURN = '3497'
...     SEA_GREEN = '1246'
...     BLEACHED_CORAL = () # New color, no Pantone code yet!
...
>>> Swatch.SEA_GREEN
<Swatch.SEA_GREEN: 2>
>>> Swatch.SEA_GREEN.pantone
'1246'
>>> Swatch.BLEACHED_CORAL.pantone
'unknown'
					

注意

The __new__() method, if defined, is used during creation of the Enum members; it is then replaced by Enum’s __new__() which is used after class creation for lookup of existing members.

OrderedEnum ¶

An ordered enumeration that is not based on IntEnum and so maintains the normal Enum invariants (such as not being comparable to other enumerations):

>>> class OrderedEnum(Enum):
...     def __ge__(self, other):
...         if self.__class__ is other.__class__:
...             return self.value >= other.value
...         return NotImplemented
...     def __gt__(self, other):
...         if self.__class__ is other.__class__:
...             return self.value > other.value
...         return NotImplemented
...     def __le__(self, other):
...         if self.__class__ is other.__class__:
...             return self.value <= other.value
...         return NotImplemented
...     def __lt__(self, other):
...         if self.__class__ is other.__class__:
...             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
					

DuplicateFreeEnum ¶

引发错误，若发现成员名称重复而不是创建别名：

>>> 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'
					

注意

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 unique() decorator can be used instead.

Planet ¶

若 __new__() or __init__() is defined the value of the enum member will be passed to those methods:

>>> 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)
...
>>> Planet.EARTH.value
(5.976e+24, 6378140.0)
>>> Planet.EARTH.surface_gravity
9.802652743337129
					

TimePeriod ¶

范例展示 _ignore_ 属性的用法：

>>> from datetime import timedelta
>>> class Period(timedelta, Enum):
...     "different lengths of time"
...     _ignore_ = 'Period i'
...     Period = vars()
...     for i in range(367):
...         Period['day_%d' % i] = i
...
>>> list(Period)[:2]
[<Period.day_0: datetime.timedelta(0)>, <Period.day_1: datetime.timedelta(days=1)>]
>>> list(Period)[-2:]
[<Period.day_365: datetime.timedelta(days=365)>, <Period.day_366: datetime.timedelta(days=366)>]
					

枚举有什么不同？ ¶

Enums have a custom metaclass that affects many aspects of both derived Enum classes and their instances (members).

枚举类 ¶

The EnumMeta metaclass is responsible for providing the __contains__() , __dir__() , __iter__() and other methods that allow one to do things with an Enum class that fail on a typical class, such as list(Color) or some_enum_var in Color . EnumMeta is responsible for ensuring that various other methods on the final Enum class are correct (such as __new__() , __getnewargs__() , __str__() and __repr__() ).

枚举成员 (亦称作实例) ¶

The most interesting thing about Enum members is that they are singletons. EnumMeta creates them all while it is creating the Enum class itself, and then puts a custom __new__() in place to ensure that no new ones are ever instantiated by returning only the existing member instances.

Finer Points ¶

支持 __dunder__ 名称 ¶

__members__ 是只读有序映射的 member_name : member 项。只可用于 class。

__new__() , if specified, must create and return the enum members; it is also a very good idea to set the member’s _value_ appropriately. Once all the members are created it is no longer used.

支持 _sunder_ 名称 ¶

• _name_ – 成员名称

• _value_ – 成员的值；设置/修改可以在 __new__

• _missing_ – a lookup function used when a value is not found; may be overridden

• _ignore_ – a list of names, either as a list() 或 str() , that will not be transformed into members, and will be removed from the final class

• _order_ – used in Python 2/3 code to ensure member order is consistent (class attribute, removed during class creation)

• _generate_next_value_ – 用于 函数式 API 和通过 auto to get an appropriate value for an enum member; may be overridden

3.6 版新增： _missing_ , _order_ , _generate_next_value_

3.7 版新增： _ignore_

To help keep Python 2 / Python 3 code in sync an _order_ 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:

>>> class Color(Enum):
...     _order_ = 'RED GREEN BLUE'
...     RED = 1
...     BLUE = 3
...     GREEN = 2
...
Traceback (most recent call last):
...
TypeError: member order does not match _order_
					

注意

在 Python 2 代码中 _order_ attribute is necessary as definition order is lost before it can be recorded.

Enum 成员类型 ¶

Enum 成员是实例化的 Enum class, and are normally accessed as EnumClass.member . Under certain circumstances they can also be accessed as EnumClass.member.member , but you should never do this as that lookup may fail or, worse, return something besides the Enum member you are looking for (this is another good reason to use all-uppercase names for members):

>>> class FieldTypes(Enum):
...     name = 0
...     value = 1
...     size = 2
...
>>> FieldTypes.value.size
<FieldTypes.size: 2>
>>> FieldTypes.size.value
2
					

3.5 版改变。

布尔值的 Enum 类和成员 ¶

Enum 成员混合非 Enum 类型 (譬如 int , str , etc.) are evaluated according to the mixed-in type’s rules; otherwise, all members evaluate as True . To make your own Enum’s boolean evaluation depend on the member’s value add the following to your class:

def __bool__(self):
    return bool(self.value)
					

Enum 类始终评估为 True .

Enum 类具有的方法 ¶

若给出 Enum 子类额外方法，像 Planet class above, those methods will show up in a dir() of the member, but not of the class:

>>> dir(Planet)
['EARTH', 'JUPITER', 'MARS', 'MERCURY', 'NEPTUNE', 'SATURN', 'URANUS', 'VENUS', '__class__', '__doc__', '__members__', '__module__']
>>> dir(Planet.EARTH)
['__class__', '__doc__', '__module__', 'name', 'surface_gravity', 'value']
					

组合成员为 Flag ¶

若 Flag 成员的组合未命名， repr() 将包括值中的所有命名标志和标志的所有命名组合：

>>> class Color(Flag):
...     RED = auto()
...     GREEN = auto()
...     BLUE = auto()
...     MAGENTA = RED | BLUE
...     YELLOW = RED | GREEN
...     CYAN = GREEN | BLUE
...
>>> Color(3)  # named combination
<Color.YELLOW: 3>
>>> Color(7)      # not named combination
<Color.CYAN|MAGENTA|BLUE|YELLOW|GREEN|RED: 7>
					

内容表

• enum — 支持枚举
  • 模块内容
  • 创建枚举
  • 编程方式访问枚举成员及其属性
  • 复制枚举成员和值
  • 确保唯一枚举值
  • 使用自动值
  • 迭代
  • 比较
  • 允许枚举成员和属性
  • 限定枚举子类化
  • 腌制
  • 函数式 API
  • 派生枚举
    • IntEnum
    • IntFlag
    • 标志
    • 其它
  • 当要使用 __new__() vs. __init__()
  • 有趣范例
    • 省略值
      • 使用 auto
      • 使用 object
      • 使用描述性字符串
      • 使用自定义 __new__()
    • OrderedEnum
    • DuplicateFreeEnum
    • Planet
    • TimePeriod
  • 枚举有什么不同？
    • 枚举类
    • 枚举成员 (亦称作实例)
    • Finer Points
      • 支持 __dunder__ 名称
      • 支持 _sunder_ 名称
      • Enum 成员类型
      • 布尔值的 Enum 类和成员
      • Enum 类具有的方法
      • 组合成员为 Flag

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