enum --- 열거형 지원

버전 3.4에 추가.

소스 코드: Lib/enum.py


열거형(enumeration)은 고유한 상수 값에 연결된 기호 이름(멤버)의 집합입니다. 열거형 내에서, 멤버를 아이덴티티로 비교할 수 있고, 열거형 자체는 이터레이트 될 수 있습니다.

모듈 내용

이 모듈은 고유한 이름 집합과 값을 정의하는 데 사용할 수 있는 네가지 열거형 클래스를 정의합니다: Enum, IntEnum, FlagIntFlag. 또한 하나의 데코레이터 unique()와 하나의 도우미 auto를 정의합니다.

class enum.Enum

열거형 상수를 만들기 위한 베이스 클래스. 대체 구성 문법은 함수형 API 섹션을 참조하십시오.

class enum.IntEnum

int의 서브 클래스이기도 한 열거형 상수를 만들기 위한 베이스 클래스.

class enum.IntFlag

IntFlag 멤버십을 잃지 않고 비트 연산자를 사용하여 결합할 수 있는 열거형 상수를 만들기 위한 베이스 클래스. IntFlag 멤버도 int의 서브 클래스입니다.

class enum.Flag

Flag 멤버십을 잃지 않고 비트 연산을 사용하여 결합할 수 있는 열거형 상수를 만들기 위한 베이스 클래스.

enum.unique()

한 값에 하나의 이름 만 연결되도록 하는 Enum 클래스 데코레이터.

class enum.auto

인스턴스는 Enum 멤버에 적절한 값으로 바뀝니다.

버전 3.6에 추가: Flag, IntFlag, auto

Enum 만들기

열거형은 class 문법을 사용하여 작성되므로 쉽게 읽고 쓸 수 있습니다. 대체 작성 방법은 함수형 API에 설명되어 있습니다. 열거형을 정의하려면, 다음과 같이 Enum을 서브 클래스 하십시오:

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

참고

Enum 멤버 값

멤버 값은 아무 것이나 될 수 있습니다: int, str 등. 정확한 값이 중요하지 않다면, auto 인스턴스를 사용할 수 있으며 적절한 값이 선택됩니다. auto를 다른 값과 혼합 할 경우 주의를 기울여야합니다.

참고

명명법

  • Color 클래스는 열거형(enumeration)(또는 enum)입니다.

  • Color.RED, Color.GREEN 등의 어트리뷰트는 열거형 멤버(enumeration members)(또는 enum members)이며 기능상 상수입니다.

  • 열거형 멤버에는 이름(names)값(values)이 있습니다 (Color.RED의 이름은 RED, Color.BLUE의 값은 3 등)

참고

class 문법을 사용하여 Enum을 만들더라도, Enum은 일반적인 파이썬 클래스가 아닙니다. 자세한 내용은 열거형은 어떻게 다릅니까?를 참조하십시오.

열거형 멤버는 사람이 읽을 수 있는 문자열 표현을 갖습니다:

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

repr에는 더 자세한 정보가 있습니다:

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

열거형 멤버의 은 그것이 속한 열거형입니다:

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

Enum 멤버에는 항목 이름 만 포함하는 프로퍼티가 있습니다:

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

열거형은 정의 순서로 이터레이션을 지원합니다:

>>> 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

열거형 멤버는 해시 가능하므로, 딕셔너리와 집합에 사용할 수 있습니다:

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

열거형 멤버와 그들의 어트리뷰트에 프로그래밍 방식으로 액세스하기

때로는 프로그래밍 방식으로 열거형의 멤버에 액세스하는 것이 유용합니다 (즉, 프로그램 작성 시간에 정확한 색상을 알 수 없어서 Color.RED를 쓸 수 없는 상황). Enum는 그런 액세스를 허용합니다:

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

이름(name)으로 열거형 멤버에 액세스하려면, 항목 액세스를 사용하십시오:

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

열거형 멤버가 있고 name이나 value가 필요하면:

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

열거형 멤버와 값 중복하기

이름이 같은 열거형 멤버가 두 개 있는 것은 유효하지 않습니다:

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

그러나, 두 열거형 멤버는 같은 값을 가질 수 있습니다. 같은 값을 가진 두 멤버 A와 B가 주어지면 (그리고 A가 먼저 정의되면), B는 A의 별칭입니다. A와 B의 값을 통한 조회는 A를 반환합니다. B의 이름을 통한 조회도 A를 반환합니다:

>>> 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>

참고

이미 정의된 어트리뷰트(다른 멤버, 메서드 등)와 같은 이름의 멤버를 만들려고하거나 멤버와 같은 이름의 어트리뷰트를 만들려는 시도는 허용되지 않습니다.

고유한 열거형 값 보장하기

기본적으로, 열거형은 여러 이름을 같은 값에 대한 별칭으로 허용합니다. 이 동작이 바람직하지 않을 때, 다음 데코레이터를 사용하여 각 값이 열거에서 한 번만 사용되도록 보장할 수 있습니다:

@enum.unique

열거형 용 class 데코레이터입니다. 열거형의 __members__를 검색하여 별칭을 수집합니다; 발견되면 ValueError가 세부 정보와 함께 발생합니다:

>>> 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

자동 값 사용하기

정확한 값이 중요하지 않으면, auto를 사용할 수 있습니다:

>>> 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>]

값은 _generate_next_value_()에 의해 선택되는데, 재정의할 수 있습니다:

>>> 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'>]

참고

기본 _generate_next_value_() 메서드의 목표는 제공된 마지막 int와 연속되도록 다음 int를 제공하는 것이지만, 이를 수행하는 방법은 구현 세부 사항이며 변경 될 수 있습니다.

이터레이션

열거형 멤버를 이터레이트해도 별칭은 제공되지 않습니다:

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

특수 어트리뷰트 __members__는 이름에서 멤버로의 읽기 전용 순서있는 매핑입니다. 별칭을 포함하여, 열거형에 정의된 모든 이름을 포함합니다:

>>> 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__ 어트리뷰트는 열거형 멤버에 대한 프로그래밍 방식의 자세한 액세스에 사용할 수 있습니다. 예를 들어, 모든 별칭 찾기:

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

비교

열거형 멤버는 아이덴티티로 비교됩니다:

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

열거형 값 사이의 순서 비교는 지원되지 않습니다. 열거형 멤버는 정수가 아닙니다 (그러나 아래의 IntEnum을 참조하십시오):

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

동등 비교는 정의됩니다:

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

열거형 값이 아닌 값과의 비교는 항상 다르다고 비교됩니다 (다시, IntEnum은 다르게 동작하도록 명시적으로 설계되었습니다, 아래를 참조하십시오):

>>> Color.BLUE == 2
False

열거형의 허용된 멤버와 어트리뷰트

위의 예제는 열거형 값에 정수를 사용합니다. 정수 사용은 짧고 편리하지만 (함수형 API에서 기본적으로 제공합니다), 엄격하게 강제하지는 않습니다. 대다수의 사용 사례에서, 열거의 실제 값이 무엇인지 신경 쓰지 않습니다. 그러나 값이 중요하면, 열거형은 임의의 값을 가질 수 있습니다.

열거형은 파이썬 클래스이며, 평소와 같이 메서드와 특수 메서드를 가질 수 있습니다. 이런 열거형이 있다고 합시다:

>>> class Mood(Enum):
...     FUNKY = 1
...     HAPPY = 3
...
...     def describe(self):
...         # 여기서 self는 멤버입니다
...         return self.name, self.value
...
...     def __str__(self):
...         return 'my custom str! {0}'.format(self.value)
...
...     @classmethod
...     def favorite_mood(cls):
...         # 여기서 cls는 열거형입니다
...         return cls.HAPPY
...

그러면:

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

허용되는 규칙은 다음과 같습니다: 단일 밑줄로 시작하고 끝나는 이름은 enum이 예약하고 있고 사용할 수 없습니다; 열거형 내에 정의된 다른 모든 어트리뷰트는 특수 메서드 (__str__(), __add__() 등), 디스크립터 (메서드도 디스크립터입니다) 및 _ignore_에 나열된 변수 이름을 제외하고 이 열거의 멤버가됩니다.

참고: 열거형이 __new__() 및/또는 __init__()를 정의하면 열거형 멤버에 제공된 모든 값이 해당 메서드에 전달됩니다. 예제는 행성을 참조하십시오.

제한된 Enum 서브 클래싱

새로운 Enum 클래스에는 하나의 베이스 Enum 클래스, 최대 하나의 구상 데이터 형 및 필요한만큼의 object 기반 믹스 인 클래스가 있어야합니다. 이 베이스 클래스의 순서는 다음과 같습니다:

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

또한, 열거형의 서브 클래싱은 열거형이 멤버를 정의하지 않았을 때만 허용됩니다. 따라서 다음과 같은 것은 금지되어 있습니다:

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

그러나 이것은 허용됩니다:

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

멤버를 정의하는 열거형의 서브 클래싱을 허용하면 형과 인스턴스의 중요한 불변성을 위반하게됩니다. 반면에, 열거형 그룹간에 공통적인 동작을 공유하도록 허락하는 것은 말이됩니다. (예는 OrderedEnum을 참조하십시오.)

피클링

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.

참고

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.

함수형 API

The 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 is equivalent to:

>>> 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__)

경고

If 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)
value

What the new Enum class will record as its name.

names

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}
module

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.

버전 3.5에서 변경: The start parameter was added.

Derived Enumerations

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 enumerations:

>>> 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 membership.

버전 3.6에 추가.

Sample IntFlag class:

>>> 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

Because IntFlag members are also subclasses of int they can be combined with them:

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

Flag

The last variation is Flag. Like 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.

버전 3.6에 추가.

Like 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

참고

For the majority of new code, 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.

Others

While IntEnum is part of the 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 instead of int.

Some rules:

  1. When subclassing 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 attribute is 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 class's __str__() and __repr__() respectively; other codes (such as %i or %h for IntEnum) treat the enum member as its mixed-in type.

  5. Formatted string literals, str.format(), and format() will use the mixed-in type's __format__(). If the Enum class's str() or repr() is desired, use the !s or !r format codes.

When to use __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__(), with __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

Interesting examples

While Enum, IntEnum, IntFlag, and 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.

Omitting values

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:

  • use instances of auto for the value

  • use instances of object as the value

  • use a descriptive string as the value

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

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)
...

Using auto

Using auto would look like:

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

Using object

Using object would look like:

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

Using a descriptive string

Using a string as the value would look like:

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

Using a custom __new__()

Using an auto-numbering __new__() would look like:

>>> 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

참고

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

Raises an error if a duplicate member name is found instead of creating an alias:

>>> 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'

참고

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.

행성

If __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

An example to show the _ignore_ attribute in use:

>>> 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)>]

열거형은 어떻게 다릅니까?

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

Enum Classes

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__()).

Enum Members (aka instances)

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

Supported __dunder__ names

__members__ is a read-only ordered mapping of member_name:member items. It is only available on the 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.

Supported _sunder_ names

  • _name_ -- name of the member

  • _value_ -- value of the member; can be set / modified in __new__

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

  • _ignore_ -- a list of names, either as a list() or a 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_ -- used by the Functional API and by auto to get an appropriate value for an enum member; may be overridden

버전 3.6에 추가: _missing_, _order_, _generate_next_value_

버전 3.7에 추가: _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_

참고

In Python 2 code the _order_ attribute is necessary as definition order is lost before it can be recorded.

Enum member type

Enum members are instances of their 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

버전 3.5에서 변경.

Boolean value of Enum classes and members

Enum members that are mixed with non-Enum types (such as 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 classes always evaluate as True.

Enum classes with methods

If you give your Enum subclass extra methods, like the 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']

Combining members of Flag

If a combination of Flag members is not named, the repr() will include all named flags and all named combinations of flags that are in the 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>