enum — 支持枚举 ¶

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 enum. Enum ¶

Base class for creating enumerated constants. See section 函数式 API for an alternate construction syntax.

class enum. IntEnum ¶

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

class enum. IntFlag ¶

Base class for creating enumerated constants that can be combined using the bitwise operators without losing their IntFlag 成员资格。 IntFlag members are also subclasses of int .

class enum. Flag ¶

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

enum. unique ( )

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

class enum. auto ¶

Instances are replaced with an appropriate value for Enum members. By default, the initial value starts at 1.

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
...
								

Enumeration members have human readable string representations:

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

…while their repr has more information:

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

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

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

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

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

Enumerations support iteration, in definition order:

>>> 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 ¶

Having two enum members with the same name is invalid:

>>> 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>
								

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:

@ enum. 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 ¶

If the exact value is unimportant you can use 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'>]
								

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>)
								

__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 any value(s) given to the enum member will be passed into those methods. See Planet 范例。

限定枚举子类化 ¶

A new 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.

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

函数式 API ¶

Enum class is callable, providing the following functional API:

>>> 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__)
								

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)
								

value

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'
										

or an iterator of names:

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

or an iterator of (name, value) pairs:

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

or a mapping:

{'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

type to mix in to new Enum class.

start

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

派生枚举 ¶

>>> 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
									

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

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

>>> 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
									

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

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

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

>>> 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
									

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

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

class IntEnum(int, Enum):
    pass
									

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.

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

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

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

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

>>> 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
										

>>> 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
...
										

>>> 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'
										

>>> 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
									

>>> 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'
									

>>> 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
									

>>> 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).

>>> 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_
										

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

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

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

>>> 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>