内容表

  • Enum HOWTO
    • 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
    • Dataclass support
    • 腌制
    • 函数式 API
    • 派生枚举
      • IntEnum
      • StrEnum
      • IntFlag
      • 标志
      • 其它
    • 当要使用 __new__() vs. __init__()
      • Finer Points
        • 支持 __dunder__ 名称
        • 支持 _sunder_ 名称
        • _Private__names
        • Enum 成员类型
        • Creating members that are mixed with other data types
        • 布尔值的 Enum 类和成员
        • Enum 类具有的方法
        • 组合成员为 Flag
        • Flag and IntFlag minutia
    • How are Enums and Flags different?
      • 枚举类
      • Flag Classes
      • 枚举成员 (亦称作实例)
      • Flag Members
    • Enum Cookbook
      • 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
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      8. Enum HOWTO

      Enum HOWTO ¶

      An Enum is a set of symbolic names bound to unique values. They are similar to global variables, but they offer a more useful repr() , grouping, type-safety, and a few other features.

      They are most useful when you have a variable that can take one of a limited selection of values. For example, the days of the week: 

      >>> from enum import Enum
>>> class Weekday(Enum):
...     MONDAY = 1
...     TUESDAY = 2
...     WEDNESDAY = 3
...     THURSDAY = 4
...     FRIDAY = 5
...     SATURDAY = 6
...     SUNDAY = 7

      Or perhaps the RGB primary colors: 

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

      As you can see, creating an Enum is as simple as writing a class that inherits from Enum 本身。

      注意

      枚举成员案例

      Because Enums are used to represent constants, and to help avoid issues with name clashes between mixin-class methods/attributes and enum names, we strongly recommend using UPPER_CASE names for members, and will be using that style in our examples.

      Depending on the nature of the enum a member’s value may or may not be important, but either way that value can be used to get the corresponding member: 

      >>> Weekday(3)
<Weekday.WEDNESDAY: 3>

      As you can see, the repr() of a member shows the enum name, the member name, and the value. The str() of a member shows only the enum name and member name: 

      >>> print(Weekday.THURSDAY)
Weekday.THURSDAY

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

      >>> type(Weekday.MONDAY)
<enum 'Weekday'>
>>> isinstance(Weekday.FRIDAY, Weekday)
True

      Enum members have an attribute that contains just their name : 

      >>> print(Weekday.TUESDAY.name)
TUESDAY

      Likewise, they have an attribute for their value : 

      >>> Weekday.WEDNESDAY.value
3

      Unlike many languages that treat enumerations solely as name/value pairs, Python Enums can have behavior added. For example, datetime.date has two methods for returning the weekday: weekday() and isoweekday() . The difference is that one of them counts from 0-6 and the other from 1-7. Rather than keep track of that ourselves we can add a method to the Weekday enum to extract the day from the date instance and return the matching enum member: 

      @classmethod
def from_date(cls, date):
    return cls(date.isoweekday())

      The complete Weekday enum now looks like this: 

      >>> class Weekday(Enum):
...     MONDAY = 1
...     TUESDAY = 2
...     WEDNESDAY = 3
...     THURSDAY = 4
...     FRIDAY = 5
...     SATURDAY = 6
...     SUNDAY = 7
...     #
...     @classmethod
...     def from_date(cls, date):
...         return cls(date.isoweekday())

      Now we can find out what today is! Observe: 

      >>> from datetime import date
>>> Weekday.from_date(date.today())
<Weekday.TUESDAY: 2>

      Of course, if you’re reading this on some other day, you’ll see that day instead.

      This Weekday enum is great if our variable only needs one day, but what if we need several? Maybe we’re writing a function to plot chores during a week, and don’t want to use a list – we could use a different type of Enum : 

      >>> from enum import Flag
>>> class Weekday(Flag):
...     MONDAY = 1
...     TUESDAY = 2
...     WEDNESDAY = 4
...     THURSDAY = 8
...     FRIDAY = 16
...     SATURDAY = 32
...     SUNDAY = 64

      We’ve changed two things: we’re inherited from Flag , and the values are all powers of 2.

      Just like the original Weekday enum above, we can have a single selection: 

      >>> first_week_day = Weekday.MONDAY
>>> first_week_day
<Weekday.MONDAY: 1>

      But Flag also allows us to combine several members into a single variable: 

      >>> weekend = Weekday.SATURDAY | Weekday.SUNDAY
>>> weekend
<Weekday.SATURDAY|SUNDAY: 96>

      You can even iterate over a Flag 变量： 

      >>> for day in weekend:
...     print(day)
Weekday.SATURDAY
Weekday.SUNDAY

      Okay, let’s get some chores set up: 

      >>> chores_for_ethan = {
...     'feed the cat': Weekday.MONDAY | Weekday.WEDNESDAY | Weekday.FRIDAY,
...     'do the dishes': Weekday.TUESDAY | Weekday.THURSDAY,
...     'answer SO questions': Weekday.SATURDAY,
...     }

      And a function to display the chores for a given day: 

      >>> def show_chores(chores, day):
...     for chore, days in chores.items():
...         if day in days:
...             print(chore)
...
>>> show_chores(chores_for_ethan, Weekday.SATURDAY)
answer SO questions

      In cases where the actual values of the members do not matter, you can save yourself some work and use auto() for the values: 

      >>> from enum import auto
>>> class Weekday(Flag):
...     MONDAY = auto()
...     TUESDAY = auto()
...     WEDNESDAY = auto()
...     THURSDAY = auto()
...     FRIDAY = auto()
...     SATURDAY = auto()
...     SUNDAY = auto()
...     WEEKEND = SATURDAY | SUNDAY

      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: 'SQUARE' already defined as 2

      However, an enum member can have other names associated with it. Given two entries A and B with the same value (and A defined first), B is an alias for the member A . By-value lookup of the value of A will return the member A . By-name lookup of A will return the member A . By-name lookup of B will also return the member 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, you can use the unique() decorator: 

      >>> 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()
...
>>> [member.value for member in Color]
[1, 2, 3]

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

      >>> class AutoName(Enum):
...     @staticmethod
...     def _generate_next_value_(name, start, count, last_values):
...         return name
...
>>> class Ordinal(AutoName):
...     NORTH = auto()
...     SOUTH = auto()
...     EAST = auto()
...     WEST = auto()
...
>>> [member.value for member in Ordinal]
['NORTH', 'SOUTH', 'EAST', 'WEST']

      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>]
>>> list(Weekday)
[<Weekday.MONDAY: 1>, <Weekday.TUESDAY: 2>, <Weekday.WEDNESDAY: 4>, <Weekday.THURSDAY: 8>, <Weekday.FRIDAY: 16>, <Weekday.SATURDAY: 32>, <Weekday.SUNDAY: 64>]

      Note that the aliases Shape.ALIAS_FOR_SQUARE and Weekday.WEEKEND aren’t shown.

      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']

      注意

      Aliases for flags include values with multiple flags set, such as 3 , and no flags set, i.e. 0 .

      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

      警告

      It is possible to reload modules – if a reloaded module contains enums, they will be recreated, and the new members may not compare identical/equal to the original members.

      允许枚举成员和属性 ¶

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

      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. See When to use __new__() vs. __init__() 了解更多细节。

      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: <enum 'MoreColor'> cannot extend <enum 'Color'>

      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.)

      Dataclass support ¶

      When inheriting from a dataclass ， __repr__() omits the inherited class’ name. For example: 

      >>> from dataclasses import dataclass, field
>>> @dataclass
... class CreatureDataMixin:
...     size: str
...     legs: int
...     tail: bool = field(repr=False, default=True)
...
>>> class Creature(CreatureDataMixin, Enum):
...     BEETLE = 'small', 6
...     DOG = 'medium', 4
...
>>> Creature.DOG
<Creature.DOG: size='medium', legs=4>

      使用 dataclass() argument repr=False to use the standard repr() .

      Changed in version 3.12: Only the dataclass fields are shown in the value area, not the dataclass’ name.

      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. The default method is by-value, but enums with complicated values may want to use by-name: 

      >>> import enum
>>> class MyEnum(enum.Enum):
...     __reduce_ex__ = enum.pickle_by_enum_name

      注意

      Using by-name for flags is not recommended, as unnamed aliases will not unpickle.

      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>
>>> 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 by default 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 a 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,
    )

      • 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'

        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 : type to mix in to new enum class.

      • 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]

      StrEnum ¶

      The second variation of Enum that is provided is also a subclass of str . Members of a StrEnum can be compared to strings; by extension, string enumerations of different types can also be compared to each other.

      Added in version 3.11.

      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, if possible. Like IntEnum , IntFlag members are also integers and can be used wherever an int 被使用。

      注意

      Any operation on an IntFlag member besides the bit-wise operations will lose the IntFlag 成员资格。

      Bit-wise operations that result in invalid IntFlag values will lose the IntFlag membership. See FlagBoundary 了解细节。

      Added in version 3.6.

      Changed in version 3.11.

      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: 0>
>>> Perm(7)
<Perm.RWX: 7>

      注意

      Named combinations are considered aliases. Aliases do not show up during iteration, but can be returned from by-value lookups.

      Changed in version 3.11.

      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>
>>> bool(Perm.R & Perm.X)
False

      因为 IntFlag 成员也是子类的 int they can be combined with them (but may lose IntFlag membership: 

      >>> Perm.X | 4
<Perm.R|X: 5>
>>> Perm.X + 8
9

      注意

      The negation operator, ~ , always returns an IntFlag member with a positive value: 

      >>> (~Perm.X).value == (Perm.R|Perm.W).value == 6
True

      IntFlag members can also be iterated over: 

      >>> list(RW)
[<Perm.R: 4>, <Perm.W: 2>]

      Added in version 3.11.

      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.

      Added in version 3.6.

      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>
>>> bool(Color.RED & Color.GREEN)
False

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

      >>> 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

      Flag members can also be iterated over: 

      >>> purple = Color.RED | Color.BLUE
>>> list(purple)
[<Color.RED: 1>, <Color.BLUE: 2>]

      Added in version 3.11.

      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 FloatEnum that mixes in float 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. Mix-in types must be subclassable. For example, bool and range are not subclassable and will throw an error during Enum creation if used as the mix-in type.

      3. 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 type.

      4. 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.

      5. A data type is a mixin that defines __new__() ，或 dataclass

      6. %-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.

      7. 格式化字符串文字 , str.format() ，和 format() will use the enum’s __str__() 方法。

      注意

      因为 IntEnum , IntFlag ，和 StrEnum are designed to be drop-in replacements for existing constants, their __str__() method has been reset to their data types’ __str__() 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

      警告

      Do not call super().__new__() , as the lookup-only __new__ is the one that is found; instead, use the data type directly.

      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

      注意

      For standard Enum classes the next value chosen is the last value seen incremented by one.

      For Flag classes the next value chosen will be the next highest power-of-two, regardless of the last value seen.

      Added in version 3.6: _missing_ , _order_ , _generate_next_value_

      Added in version 3.7: _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_:
  ['RED', 'BLUE', 'GREEN']
  ['RED', 'GREEN', 'BLUE']

      注意

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

      _Private__names ¶

      Private names are not converted to enum members, but remain normal attributes.

      Changed in version 3.11.

      Enum 成员类型 ¶

      Enum members are instances of their enum class, and are normally accessed as EnumClass.member . In certain situations, such as writing custom enum behavior, being able to access one member directly from another is useful, and is supported; however, in order to avoid name clashes between member names and attributes/methods from mixed-in classes, upper-case names are strongly recommended.

      3.5 版改变。

      Creating members that are mixed with other data types ¶

      When subclassing other data types, such as int or str , with an Enum , all values after the = are passed to that data type’s constructor. For example: 

      >>> class MyEnum(IntEnum):      # help(int) -> int(x, base=10) -> integer
...     example = '11', 16      # so x='11' and base=16
...
>>> MyEnum.example.value        # and hex(11) is...
17

      布尔值的 Enum 类和成员 ¶

      Enum classes that are mixed with non- 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)

      Plain Enum 类始终评估为 True .

      Enum 类具有的方法 ¶

      If you give your enum subclass extra methods, like the Planet class below, 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__', 'mass', 'name', 'radius', 'surface_gravity', 'value']

      组合成员为 Flag ¶

      Iterating over a combination of Flag members will only return the members that are comprised of a single bit: 

      >>> 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.RED|GREEN|BLUE: 7>

      Flag and IntFlag minutia ¶

      Using the following snippet for our examples: 

      >>> class Color(IntFlag):
...     BLACK = 0
...     RED = 1
...     GREEN = 2
...     BLUE = 4
...     PURPLE = RED | BLUE
...     WHITE = RED | GREEN | BLUE
...

      the following are true:

      • single-bit flags are canonical

      • multi-bit and zero-bit flags are aliases

      • only canonical flags are returned during iteration: 

        >>> list(Color.WHITE)
[<Color.RED: 1>, <Color.GREEN: 2>, <Color.BLUE: 4>]

      • negating a flag or flag set returns a new flag/flag set with the corresponding positive integer value: 

        >>> Color.BLUE
<Color.BLUE: 4>
>>> ~Color.BLUE
<Color.RED|GREEN: 3>

      • names of pseudo-flags are constructed from their members’ names: 

        >>> (Color.RED | Color.GREEN).name
'RED|GREEN'

      • multi-bit flags, aka aliases, can be returned from operations: 

        >>> Color.RED | Color.BLUE
<Color.PURPLE: 5>
>>> Color(7)  # or Color(-1)
<Color.WHITE: 7>
>>> Color(0)
<Color.BLACK: 0>

      • membership / containment checking: zero-valued flags are always considered to be contained: 

        >>> Color.BLACK in Color.WHITE
True

        otherwise, only if all bits of one flag are in the other flag will True be returned: 

        >>> Color.PURPLE in Color.WHITE
True
>>> Color.GREEN in Color.PURPLE
False

      There is a new boundary mechanism that controls how out-of-range / invalid bits are handled: STRICT , CONFORM , EJECT ，和 KEEP :

      • STRICT –> raises an exception when presented with invalid values

      • CONFORM –> discards any invalid bits

      • EJECT –> lose Flag status and become a normal int with the given value

      • KEEP –> keep the extra bits

        • keeps Flag status and extra bits

        • extra bits do not show up in iteration

        • extra bits do show up in repr() and str()

      The default for Flag is STRICT , the default for IntFlag is EJECT , and the default for _convert_ is KEEP (见 ssl.Options for an example of when KEEP is needed).

      How are Enums and Flags different? ¶

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

      枚举类 ¶

      The EnumType 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 . EnumType is responsible for ensuring that various other methods on the final Enum class are correct (such as __new__() , __getnewargs__() , __str__() and __repr__() ).

      Flag Classes ¶

      Flags have an expanded view of aliasing: to be canonical, the value of a flag needs to be a power-of-two value, and not a duplicate name. So, in addition to the Enum definition of alias, a flag with no value (a.k.a. 0 ) or with more than one power-of-two value (e.g. 3 ) is considered an alias.

      枚举成员 (亦称作实例) ¶

      The most interesting thing about enum members is that they are singletons. EnumType 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.

      Flag Members ¶

      Flag members can be iterated over just like the Flag class, and only the canonical members will be returned. For example: 

      >>> list(Color)
[<Color.RED: 1>, <Color.GREEN: 2>, <Color.BLUE: 4>]

      (注意， BLACK , PURPLE ，和 WHITE do not show up.)

      Inverting a flag member returns the corresponding positive value, rather than a negative value — for example: 

      >>> ~Color.RED
<Color.GREEN|BLUE: 6>

      Flag members have a length corresponding to the number of power-of-two values they contain. For example: 

      >>> len(Color.PURPLE)
2

      Enum Cookbook ¶

      While Enum , IntEnum , StrEnum , Flag ，和 IntFlag 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.

      使用 auto ¶

      使用 auto 将看起来像： 

      >>> class Color(Enum):
...     RED = auto()
...     BLUE = auto()
...     GREEN = auto()
...
>>> Color.GREEN
<Color.GREEN: 3>

      使用 object ¶

      使用 object 将看起来像： 

      >>> class Color(Enum):
...     RED = object()
...     GREEN = object()
...     BLUE = object()
...
>>> Color.GREEN
<Color.GREEN: <object object at 0x...>>

      This is also a good example of why you might want to write your own __repr__() : 

      >>> class Color(Enum):
...     RED = object()
...     GREEN = object()
...     BLUE = object()
...     def __repr__(self):
...         return "<%s.%s>" % (self.__class__.__name__, self._name_)
...
>>> 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(Enum):
...     RED = 'stop'
...     GREEN = 'go'
...     BLUE = 'too fast!'
...
>>> Color.GREEN
<Color.GREEN: 'go'>

      使用自定义 __new__() ¶

      使用自动编号 __new__() 将看起来像： 

      >>> class AutoNumber(Enum):
...     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: 2>

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

      >>> class AutoNumber(Enum):
...     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.

      警告

      Do not call super().__new__() , as the lookup-only __new__ is the one that is found; instead, use the data type directly – e.g.: 

      obj = int.__new__(cls, value)

      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 value 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'

      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)>]

      Subclassing EnumType ¶

      While most enum needs can be met by customizing Enum subclasses, either with class decorators or custom functions, EnumType can be subclassed to provide a different Enum experience.

      内容表

      • Enum HOWTO
        • 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
        • Dataclass support
        • 腌制
        • 函数式 API
        • 派生枚举
          • IntEnum
          • StrEnum
          • IntFlag
          • 标志
          • 其它
        • 当要使用 __new__() vs. __init__()
          • Finer Points
            • 支持 __dunder__ 名称
            • 支持 _sunder_ 名称
            • _Private__names
            • Enum 成员类型
            • Creating members that are mixed with other data types
            • 布尔值的 Enum 类和成员
            • Enum 类具有的方法
            • 组合成员为 Flag
            • Flag and IntFlag minutia
        • How are Enums and Flags different?
          • 枚举类
          • Flag Classes
          • 枚举成员 (亦称作实例)
          • Flag Members
        • Enum Cookbook
          • 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
        • Subclassing EnumType

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