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 itself.

Catatan

Wielkość liter literałów wyliczeniowych

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 variable:

>>> 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

Програмний доступ до елементів переліку та їх атрибутів¶

Іноді корисно отримати доступ до членів у перерахуваннях програмно (тобто ситуації, коли Color.RED не підійде, оскільки точний колір невідомий під час написання програми). Enum дозволяє такий доступ:

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

Якщо ви хочете отримати доступ до членів enum за ім’ям, використовуйте доступ до елемента:

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

If you have an enum member and need its name or value:

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

Дублювання членів enum і значень¶

Наявність двох членів переліку з однаковими іменами недійсна:

>>> 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>

Catatan

Спроба створити член із тим же ім’ям, що й уже визначений атрибут (інший член, метод тощо), або спроба створити атрибут із тим же ім’ям, що й член, не дозволяється.

Забезпечення унікальних значень перерахування¶

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

Використання автоматичних значень¶

Якщо точне значення неважливе, ви можете використовувати 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']

Catatan

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

Iteracja¶

Перебір членів enum не забезпечує псевдоніми:

>>> 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.

Спеціальний атрибут __members__ — це впорядковане відображення імен учасників лише для читання. Він включає всі імена, визначені в переліку, включаючи псевдоніми:

>>> 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>)

Атрибут __members__ можна використовувати для детального програмного доступу до елементів переліку. Наприклад, пошук усіх псевдонімів:

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

Catatan

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

Perbandingan¶

Члени переліку порівнюються за ідентичністю:

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

Упорядковані порівняння між значеннями перерахування не підтримуються. Члени Enum не є цілими числами (але дивіться IntEnum нижче):

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

Однак порівняння рівності визначено:

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

Порівняння зі значеннями, не пов’язаними з перерахуванням, завжди порівнюватиметься нерівними (знову ж таки, IntEnum був явно розроблений для іншої поведінки, див. нижче):

>>> Color.BLUE == 2
False

Peringatan

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.

Дозволені члени та атрибути перерахувань¶

Most of the examples above use integers for enumeration values. Using integers is short and handy (and provided by default by the Functional 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.

Перерахування є класами Python і, як зазвичай, можуть мати методи та спеціальні методи. Якщо ми маємо цей перелік:

>>> 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
...

Потім:

>>> 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 for an example.

Catatan

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__() for more details.

Обмежений підклас Enum¶

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

Крім того, створення підкласу переліку дозволяється, лише якщо перелік не визначає жодних членів. Тому це заборонено:

>>> class MoreColor(Color):
...     PINK = 17
...
Traceback (most recent call last):
...
TypeError: <enum 'MoreColor'> cannot extend <enum 'Color'>

Але це дозволено:

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

Дозвіл створення підкласів для переліків, які визначають члени, призведе до порушення деяких важливих інваріантів типів і екземплярів. З іншого боку, має сенс дозволити спільну поведінку між групою перерахувань. (Див. OrderedEnum для прикладу.)

Dataclass support¶

When inheriting from a dataclass, the __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>

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

Berubah pada versi 3.12: Only the dataclass fields are shown in the value area, not the dataclass' name.

Catatan

Adding dataclass() decorator to Enum and its subclasses is not supported. It will not raise any errors, but it will produce very strange results at runtime, such as members being equal to each other:

>>> @dataclass               # don't do this: it does not make any sense
... class Color(Enum):
...    RED = 1
...    BLUE = 2
...
>>> Color.RED is Color.BLUE
False
>>> Color.RED == Color.BLUE  # problem is here: they should not be equal
True

Соління¶

Перерахування можна маринувати і не маринувати:

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

Застосовуються звичайні обмеження для маркування: переліки, які можна піклувати, повинні бути визначені на верхньому рівні модуля, оскільки для скасування потрібно, щоб їх можна було імпортувати з цього модуля.

Catatan

За допомогою протоколу pickle версії 4 можна легко маринувати переліки, вкладені в інші класи.

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

Catatan

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

Функціональний API¶

Клас Enum можна викликати, забезпечуючи такий функціональний API:

>>> 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>]

Семантика цього API нагадує namedtuple. Першим аргументом виклику Enum є назва переліку.

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 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__)

Peringatan

Якщо module не вказано, і Enum не може визначити, що це таке, нові члени Enum не можна буде вибрати; щоб зберегти помилки ближче до джерела, травлення буде вимкнено.

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')

Повний підпис:

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'
```
або ітератор імен:
```
['RED', 'GREEN', 'BLUE']
```
або ітератор пар (ім'я, значення):
```
[('CYAN', 4), ('MAGENTA', 5), ('YELLOW', 6)]
```
або відображення:
```
{'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.

Berubah pada versi 3.5: Додано параметр start.

Похідні перерахування¶

IntEnum¶

Перший наданий варіант Enum також є підкласом int. Члени IntEnum можна порівняти з цілими числами; за розширенням, цілочисельні перерахування різних типів також можна порівнювати один з одним:

>>> 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

Однак їх все ще не можна порівняти зі стандартними перерахуваннями Enum:

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

Значення IntEnum поводяться як цілі числа іншим чином:

>>> 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 is used.

Catatan

Any operation on an IntFlag member besides the bit-wise operations will lose the IntFlag membership.

Bit-wise operations that result in invalid IntFlag values will lose the IntFlag membership. See FlagBoundary for details.

Added in version 3.6.

Berubah pada versi 3.11.

Приклад 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

Також можна назвати комбінації:

>>> 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>

Catatan

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

Berubah pada versi 3.11.

Ще одна важлива відмінність між IntFlag і Enum полягає в тому, що якщо не встановлено жодного прапора (значення дорівнює 0), його логічна оцінка буде False:

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

Because IntFlag members are also subclasses of int they can be combined with them (but may lose IntFlag membership:

>>> Perm.X | 4
<Perm.R|X: 5>

>>> Perm.X + 8
9

Catatan

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.

Penanda¶

Останнім варіантом є Flag. Подібно до IntFlag, члени Flag можна комбінувати за допомогою порозрядних операторів (&, |, ^, ~). На відміну від IntFlag, їх не можна комбінувати з будь-яким іншим переліком Flag або int, ані порівнювати з ними. Хоча можна вказати значення безпосередньо, рекомендується використовувати auto як значення, а Flag вибрати відповідне значення.

Added in version 3.6.

Подібно до IntFlag, якщо комбінація членів Flag не призводить до встановлення прапорів, логічна оцінка буде 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>

Присвоєння назви умові "прапори не встановлено" не змінює її логічного значення:

>>> 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.

Catatan

Для більшості нового коду наполегливо рекомендується використовувати Enum і Flag, оскільки IntEnum і IntFlag порушують деякі семантичні обіцянки перерахування (через їх порівняння з цілі числа, і, таким чином, через перехідність до інших непов’язаних перерахувань). IntEnum і IntFlag слід використовувати лише у випадках, коли Enum і Flag не підходять; наприклад, коли цілі константи замінюються перерахуваннями або для взаємодії з іншими системами.

Inne¶

Хоча IntEnum є частиною модуля enum, його було б дуже просто реалізувати незалежно:

class IntEnum(int, ReprEnum):   # or Enum instead of ReprEnum
    pass

This demonstrates how similar derived enumerations can be defined; for example a FloatEnum that mixes in float instead of int.

Деякі правила:

When subclassing Enum, mix-in types must appear before the Enum class itself in the sequence of bases, as in the IntEnum example above.
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.
Хоча Enum може мати члени будь-якого типу, коли ви додаєте додатковий тип, усі члени повинні мати значення цього типу, наприклад. int вище. Це обмеження не стосується змішувань, які лише додають методи і не вказують інший тип.
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.
A data type is a mixin that defines __new__(), or a dataclass
%-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.
Formatted string literals, str.format(), and format() will use the enum's __str__() method.

Catatan

Because IntEnum, IntFlag, and StrEnum are designed to be drop-in replacements for existing constants, their __str__() method has been reset to their data types' __str__() method.

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.

Наприклад, якщо ви хочете передати кілька елементів у конструктор, але хочете, щоб лише один із них був значенням:

>>> 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

Peringatan

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

Більш тонкі точки¶

Підтримувані імена `dunder`¶

__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.

Підтримувані імена `_sunder_`¶

_name_ -- name of the member
_value_ -- value of the member; can be set 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
_generate_next_value_() -- used to get an appropriate value for an enum member; may be overridden
_add_alias_() -- adds a new name as an alias to an existing member.
_add_value_alias_() -- adds a new value as an alias to an existing member. See MultiValueEnum for an example.

Catatan

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

For Flag classes the next value chosen will be the next highest power-of-two.

Berubah pada versi 3.13: Prior versions would use the last seen value instead of the highest value.

Added in version 3.6: _missing_, _order_, _generate_next_value_

Added in version 3.7: _ignore_

Added in version 3.13: _add_alias_, _add_value_alias_

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']

Catatan

In Python 2 code the _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.

Berubah pada versi 3.11.

Тип члена `Enum`¶

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.

Berubah pada versi 3.5.

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

Логічне значення класів і членів `Enum`¶

Enum classes 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)

Plain Enum classes always evaluate as True.

`Enum` класи з методами¶

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']

Об'єднання членів `Прапора`¶

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'

>>> class Perm(IntFlag):
...     R = 4
...     W = 2
...     X = 1
...
>>> (Perm.R & Perm.W).name is None  # effectively Perm(0)
True

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, and 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 (see 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).

Класи Enum¶

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.

Члени Enum (також відомі як екземпляри)¶

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>]

(Note that BLACK, PURPLE, and 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, and 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.

Пропуск значень¶

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:

використовувати екземпляри auto для значення
використовуйте екземпляри object як значення
використовуйте описовий рядок як значення
use a tuple as the value and a custom __new__() to replace the tuple with an int value

Використання будь-якого з цих методів означає для користувача, що ці значення не є важливими, а також дозволяє додавати, видаляти або змінювати порядок членів без необхідності перенумеровувати решту членів.

Використання `auto`¶

Використання auto виглядатиме так:

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

Використання `object`¶

Використання object виглядатиме так:

>>> 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>

Використання описового рядка¶

Використання рядка як значення виглядатиме так:

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

Using a custom `new()`¶

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

>>> 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>

Щоб зробити AutoNumber більш загального призначення, додайте *args до підпису:

>>> 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
...

Тоді, коли ви успадкуєте від AutoNumber, ви можете написати свій власний __init__ для обробки будь-яких додаткових аргументів:

>>> 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'

Catatan

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.

Peringatan

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¶

Упорядковане перерахування, яке не базується на IntEnum і тому підтримує звичайні інваріанти Enum (наприклад, не порівнюється з іншими переліками):

>>> 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'

Catatan

Це корисний приклад для підкласу Enum для додавання або зміни іншої поведінки, а також заборони псевдонімів. Якщо єдиною бажаною зміною є заборона псевдонімів, натомість можна використати декоратор unique().

MultiValueEnum¶

Supports having more than one value per member:

>>> class MultiValueEnum(Enum):
...     def __new__(cls, value, *values):
...         self = object.__new__(cls)
...         self._value_ = value
...         for v in values:
...             self._add_value_alias_(v)
...         return self
...
>>> class DType(MultiValueEnum):
...     float32 = 'f', 8
...     double64 = 'd', 9
...
>>> DType('f')
<DType.float32: 'f'>
>>> DType(9)
<DType.double64: 'd'>

Планета¶

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

Період часу¶

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)>]

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.

Enum HOWTO¶

Програмний доступ до елементів переліку та їх атрибутів¶

Дублювання членів enum і значень¶

Забезпечення унікальних значень перерахування¶

Використання автоматичних значень¶

Iteracja¶

Perbandingan¶

Дозволені члени та атрибути перерахувань¶

Обмежений підклас Enum¶

Dataclass support¶

Соління¶

Функціональний API¶

Похідні перерахування¶

IntEnum¶

StrEnum¶

IntFlag¶

Penanda¶

Inne¶

When to use __new__() vs. __init__()¶

Більш тонкі точки¶

Підтримувані імена __dunder__¶

Підтримувані імена _sunder_¶

_Private__names¶

Тип члена Enum¶

Creating members that are mixed with other data types¶

Логічне значення класів і членів Enum¶

Enum класи з методами¶

Об'єднання членів Прапора¶

Flag and IntFlag minutia¶

How are Enums and Flags different?¶

Класи Enum¶

Flag Classes¶

Члени Enum (також відомі як екземпляри)¶

Flag Members¶

Enum Cookbook¶

Пропуск значень¶

Використання auto¶

Використання object¶

Використання описового рядка¶

Using a custom __new__()¶

OrderedEnum¶

DuplicateFreeEnum¶

MultiValueEnum¶

Планета¶

Період часу¶

Subclassing EnumType¶

When to use `new()` vs. `init()`¶

Підтримувані імена `dunder`¶

Підтримувані імена `_sunder_`¶

Тип члена `Enum`¶

Логічне значення класів і членів `Enum`¶

`Enum` класи з методами¶

Об'єднання членів `Прапора`¶

`Flag` and `IntFlag` minutia¶

Використання `auto`¶

Використання `object`¶

Using a custom `new()`¶