enum — 对枚举的支持

3.4 新版功能.

源代码： Lib/enum.py

An enumeration:

  • is a set of symbolic names (members) bound to unique values

  • can be iterated over to return its members in definition order

  • uses call syntax to return members by value

  • uses index syntax to return members by name

Enumerations are created either by using class syntax, or by using function-call syntax:

>>> from enum import Enum

>>> # class syntax
>>> class Color(Enum):
...     RED = 1
...     GREEN = 2
...     BLUE = 3

>>> # functional syntax
>>> Color = Enum('Color', ['RED', 'GREEN', 'BLUE'])

Even though we can use class syntax to create Enums, Enums are not normal Python classes. See How are Enums different? for more details.

备注

命名法

  • 类 Color 是 枚举 （或称为 enum ）。

  • The attributes Color.RED, Color.GREEN, etc., are enumeration members (or members) and are functionally constants.

  • 枚举成员具有 名称 和 值 (例如 Color.RED 的名称为 RED，Color.BLUE 的值为 3 等等)

模块内容

EnumType

The type for Enum and its subclasses.

Enum

Base class for creating enumerated constants.

IntEnum

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

StrEnum

Base class for creating enumerated constants that are also subclasses of str. (Notes)

Flag

创建可与位运算符搭配使用，又不会失去 Flag 成员资格的枚举常量的基类。

IntFlag

Base class for creating enumerated constants that can be combined using the bitwise operators without losing their IntFlag membership. IntFlag members are also subclasses of int. (Notes)

EnumCheck

An enumeration with the values CONTINUOUS, NAMED_FLAGS, and UNIQUE, for use with verify() to ensure various constraints are met by a given enumeration.

FlagBoundary

An enumeration with the values STRICT, CONFORM, EJECT, and KEEP which allows for more fine-grained control over how invalid values are dealt with in an enumeration.

auto

Instances are replaced with an appropriate value for Enum members. StrEnum defaults to the lower-cased version of the member name, while other Enums default to 1 and increase from there.

property()

Allows Enum members to have attributes without conflicting with member names.

unique()

确保一个名称只绑定一个值的 Enum 类装饰器。

verify()

Enum class decorator that checks user-selectable constraints on an enumeration.

member()

Make obj a member. Can be used as a decorator.

nonmember()

Do not make obj a member. Can be used as a decorator.

3.6 新版功能: Flag, IntFlag, auto

3.11 新版功能: StrEnum, EnumCheck, FlagBoundary, property, member, nonmember

Data Types

class enum.EnumType

EnumType is the metaclass for enum enumerations. It is possible to subclass EnumType – see Subclassing EnumType for details.

EnumType is responsible for setting the correct __repr__(), __str__(), __format__(), and __reduce__() methods on the final enum, as well as creating the enum members, properly handling duplicates, providing iteration over the enum class, etc.

__contains__(cls, member)

Returns True if member belongs to the cls:

>>> some_var = Color.RED
>>> some_var in Color
True

备注

In Python 3.12 it will be possible to check for member values and not just members; until then, a TypeError will be raised if a non-Enum-member is used in a containment check.

__dir__(cls)

Returns ['__class__', '__doc__', '__members__', '__module__'] and the names of the members in cls:

>>> dir(Color)
['BLUE', 'GREEN', 'RED', '__class__', '__contains__', '__doc__', '__getitem__', '__init_subclass__', '__iter__', '__len__', '__members__', '__module__', '__name__', '__qualname__']
__getitem__(cls, name)

Returns the Enum member in cls matching name, or raises an KeyError:

>>> Color['BLUE']
<Color.BLUE: 3>
__iter__(cls)

Returns each member in cls in definition order:

>>> list(Color)
[<Color.RED: 1>, <Color.GREEN: 2>, <Color.BLUE: 3>]
__len__(cls)

Returns the number of member in cls:

>>> len(Color)
3
__reversed__(cls)

Returns each member in cls in reverse definition order:

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

Enum is the base class for all enum enumerations.

name

The name used to define the Enum member:

>>> Color.BLUE.name
'BLUE'
value

The value given to the Enum member:

>>> Color.RED.value
1

备注

Enum 成员值

成员值可以是 int、str 等。若无需设定确切值，auto 实例可以自动为成员分配合适 的值。将 auto 与其他值混用时必须要慎重。

_ignore_

_ignore_ is only used during creation and is removed from the enumeration once creation is complete.

_ignore_ is a list of names that will not become members, and whose names will also be removed from the completed enumeration. See TimePeriod for an example.

__call__(cls, value, names=None, \*, module=None, qualname=None, type=None, start=1, boundary=None)

This method is called in two different ways:

  • to look up an existing member:

    cls

    The enum class being called.

    值

    The value to lookup.

  • to use the cls enum to create a new enum:

    cls

    The enum class being called.

    值

    The name of the new Enum to create.

    names

    The names/values of the members for the new Enum.

    module – 模块

    The name of the module the new Enum is created in.

    qualname

    The actual location in the module where this Enum can be found.

    type – 类型

    A mix-in type for the new Enum.

    start

    The first integer value for the Enum (used by auto)

    boundary

    How to handle out-of-range values from bit operations (Flag only)

__dir__(self)

Returns ['__class__', '__doc__', '__module__', 'name', 'value'] and any public methods defined on self.__class__:

>>> from datetime import date
>>> class Weekday(Enum):
...     MONDAY = 1
...     TUESDAY = 2
...     WEDNESDAY = 3
...     THURSDAY = 4
...     FRIDAY = 5
...     SATURDAY = 6
...     SUNDAY = 7
...     @classmethod
...     def today(cls):
...         print('today is %s' % cls(date.today().isoweekday()).name)
>>> dir(Weekday.SATURDAY)
['__class__', '__doc__', '__eq__', '__hash__', '__module__', 'name', 'today', 'value']
_generate_next_value_(name, start, count, last_values)
name

The name of the member being defined (e.g. ‘RED’).

start

The start value for the Enum; the default is 1.

count

The number of members currently defined, not including this one.

last_values

A list of the previous values.

A staticmethod that is used to determine the next value returned by auto:

>>> from enum import auto
>>> class PowersOfThree(Enum):
...     @staticmethod
...     def _generate_next_value_(name, start, count, last_values):
...         return (count + 1) * 3
...     FIRST = auto()
...     SECOND = auto()
>>> PowersOfThree.SECOND.value
6
__init_subclass__(cls, \**kwds)

A classmethod that is used to further configure subsequent subclasses. By default, does nothing.

_missing_(cls, value)

A classmethod for looking up values not found in cls. By default it does nothing, but can be overridden to implement custom search behavior:

>>> from enum import StrEnum
>>> class Build(StrEnum):
...     DEBUG = auto()
...     OPTIMIZED = auto()
...     @classmethod
...     def _missing_(cls, value):
...         value = value.lower()
...         for member in cls:
...             if member.value == value:
...                 return member
...         return None
>>> Build.DEBUG.value
'debug'
>>> Build('deBUG')
<Build.DEBUG: 'debug'>
__repr__(self)

Returns the string used for repr() calls. By default, returns the Enum name, member name, and value, but can be overridden:

>>> class OtherStyle(Enum):
...     ALTERNATE = auto()
...     OTHER = auto()
...     SOMETHING_ELSE = auto()
...     def __repr__(self):
...         cls_name = self.__class__.__name__
...         return f'{cls_name}.{self.name}'
>>> OtherStyle.ALTERNATE, str(OtherStyle.ALTERNATE), f"{OtherStyle.ALTERNATE}"
(OtherStyle.ALTERNATE, 'OtherStyle.ALTERNATE', 'OtherStyle.ALTERNATE')
__str__(self)

Returns the string used for str() calls. By default, returns the Enum name and member name, but can be overridden:

>>> class OtherStyle(Enum):
...     ALTERNATE = auto()
...     OTHER = auto()
...     SOMETHING_ELSE = auto()
...     def __str__(self):
...         return f'{self.name}'
>>> OtherStyle.ALTERNATE, str(OtherStyle.ALTERNATE), f"{OtherStyle.ALTERNATE}"
(<OtherStyle.ALTERNATE: 1>, 'ALTERNATE', 'ALTERNATE')
__format__(self)

Returns the string used for format() and f-string calls. By default, returns __str__() returns, but can be overridden:

>>> class OtherStyle(Enum):
...     ALTERNATE = auto()
...     OTHER = auto()
...     SOMETHING_ELSE = auto()
...     def __format__(self, spec):
...         return f'{self.name}'
>>> OtherStyle.ALTERNATE, str(OtherStyle.ALTERNATE), f"{OtherStyle.ALTERNATE}"
(<OtherStyle.ALTERNATE: 1>, 'OtherStyle.ALTERNATE', 'ALTERNATE')

备注

Using auto with Enum results in integers of increasing value, starting with 1.

class enum.IntEnum

IntEnum is the same as Enum, but its members are also integers and can be used anywhere that an integer can be used. If any integer operation is performed with an IntEnum member, the resulting value loses its enumeration status.

>>> from enum import IntEnum
>>> class Numbers(IntEnum):
...     ONE = 1
...     TWO = 2
...     THREE = 3
>>> Numbers.THREE
<Numbers.THREE: 3>
>>> Numbers.ONE + Numbers.TWO
3
>>> Numbers.THREE + 5
8
>>> Numbers.THREE == 3
True

备注

Using auto with IntEnum results in integers of increasing value, starting with 1.

在 3.11 版更改: __str__() is now int.__str__() to better support the replacement of existing constants use-case. __format__() was already int.__format__() for that same reason.

class enum.StrEnum

StrEnum is the same as Enum, but its members are also strings and can be used in most of the same places that a string can be used. The result of any string operation performed on or with a StrEnum member is not part of the enumeration.

备注

There are places in the stdlib that check for an exact str instead of a str subclass (i.e. type(unknown) == str instead of isinstance(str, unknown)), and in those locations you will need to use str(StrEnum.member).

备注

Using auto with StrEnum results in the lower-cased member name as the value.

备注

__str__() is str.__str__() to better support the replacement of existing constants use-case. __format__() is likewise str.__format__() for that same reason.

3.11 新版功能.

class enum.Flag

Flag members support the bitwise operators & (AND), | (OR), ^ (XOR), and ~ (INVERT); the results of those operators are members of the enumeration.

__contains__(self, value)

Returns True if value is in self:

>>> from enum import Flag, auto
>>> class Color(Flag):
...     RED = auto()
...     GREEN = auto()
...     BLUE = auto()
>>> purple = Color.RED | Color.BLUE
>>> white = Color.RED | Color.GREEN | Color.BLUE
>>> Color.GREEN in purple
False
>>> Color.GREEN in white
True
>>> purple in white
True
>>> white in purple
False
__iter__(self):

Returns all contained members:

>>> list(Color.RED)
[<Color.RED: 1>]
>>> list(purple)
[<Color.RED: 1>, <Color.BLUE: 4>]
__len__(self):

Returns number of members in flag:

>>> len(Color.GREEN)
1
>>> len(white)
3
__bool__(self):

Returns True if any members in flag, False otherwise:

>>> bool(Color.GREEN)
True
>>> bool(white)
True
>>> black = Color(0)
>>> bool(black)
False
__or__(self, other)

Returns current flag binary or’ed with other:

>>> Color.RED | Color.GREEN
<Color.RED|GREEN: 3>
__and__(self, other)

Returns current flag binary and’ed with other:

>>> purple & white
<Color.RED|BLUE: 5>
>>> purple & Color.GREEN
<Color: 0>
__xor__(self, other)

Returns current flag binary xor’ed with other:

>>> purple ^ white
<Color.GREEN: 2>
>>> purple ^ Color.GREEN
<Color.RED|GREEN|BLUE: 7>
__invert__(self):

Returns all the flags in type(self) that are not in self:

>>> ~white
<Color: 0>
>>> ~purple
<Color.GREEN: 2>
>>> ~Color.RED
<Color.GREEN|BLUE: 6>
_numeric_repr_()

Function used to format any remaining unnamed numeric values. Default is the value’s repr; common choices are hex() and oct().

备注

Using auto with Flag results in integers that are powers of two, starting with 1.

在 3.11 版更改: The repr() of zero-valued flags has changed. It is now::

>>> Color(0) 
<Color: 0>
class enum.IntFlag

IntFlag is the same as Flag, but its members are also integers and can be used anywhere that an integer can be used.

>>> from enum import IntFlag, auto
>>> class Color(IntFlag):
...     RED = auto()
...     GREEN = auto()
...     BLUE = auto()
>>> Color.RED & 2
<Color: 0>
>>> Color.RED | 2
<Color.RED|GREEN: 3>

If any integer operation is performed with an IntFlag member, the result is not an IntFlag:

>>> Color.RED + 2
3

If a Flag operation is performed with an IntFlag member and:

  • the result is a valid IntFlag: an IntFlag is returned

  • the result is not a valid IntFlag: the result depends on the FlagBoundary setting

The repr() of unnamed zero-valued flags has changed. It is now:

>>> Color(0)
<Color: 0>

备注

Using auto with IntFlag results in integers that are powers of two, starting with 1.

在 3.11 版更改: __str__() is now int.__str__() to better support the replacement of existing constants use-case. __format__() was already int.__format__() for that same reason.

class enum.EnumCheck

EnumCheck contains the options used by the verify() decorator to ensure various constraints; failed constraints result in a ValueError.

UNIQUE

Ensure that each value has only one name:

>>> from enum import Enum, verify, UNIQUE
>>> @verify(UNIQUE)
... class Color(Enum):
...     RED = 1
...     GREEN = 2
...     BLUE = 3
...     CRIMSON = 1
Traceback (most recent call last):
...
ValueError: aliases found in <enum 'Color'>: CRIMSON -> RED
CONTINUOUS

Ensure that there are no missing values between the lowest-valued member and the highest-valued member:

>>> from enum import Enum, verify, CONTINUOUS
>>> @verify(CONTINUOUS)
... class Color(Enum):
...     RED = 1
...     GREEN = 2
...     BLUE = 5
Traceback (most recent call last):
...
ValueError: invalid enum 'Color': missing values 3, 4
NAMED_FLAGS

Ensure that any flag groups/masks contain only named flags – useful when values are specified instead of being generated by auto()

>>> from enum import Flag, verify, NAMED_FLAGS
>>> @verify(NAMED_FLAGS)
... class Color(Flag):
...     RED = 1
...     GREEN = 2
...     BLUE = 4
...     WHITE = 15
...     NEON = 31
Traceback (most recent call last):
...
ValueError: invalid Flag 'Color': aliases WHITE and NEON are missing combined values of 0x18 [use enum.show_flag_values(value) for details]

备注

CONTINUOUS and NAMED_FLAGS are designed to work with integer-valued members.

3.11 新版功能.

class enum.FlagBoundary

FlagBoundary controls how out-of-range values are handled in Flag and its subclasses.

STRICT

Out-of-range values cause a ValueError to be raised. This is the default for Flag:

>>> from enum import Flag, STRICT
>>> class StrictFlag(Flag, boundary=STRICT):
...     RED = auto()
...     GREEN = auto()
...     BLUE = auto()
>>> StrictFlag(2**2 + 2**4)
Traceback (most recent call last):
...
ValueError: <flag 'StrictFlag'> invalid value 20
    given 0b0 10100
  allowed 0b0 00111
CONFORM

Out-of-range values have invalid values removed, leaving a valid Flag value:

>>> from enum import Flag, CONFORM
>>> class ConformFlag(Flag, boundary=CONFORM):
...     RED = auto()
...     GREEN = auto()
...     BLUE = auto()
>>> ConformFlag(2**2 + 2**4)
<ConformFlag.BLUE: 4>
EJECT

Out-of-range values lose their Flag membership and revert to int. This is the default for IntFlag:

>>> from enum import Flag, EJECT
>>> class EjectFlag(Flag, boundary=EJECT):
...     RED = auto()
...     GREEN = auto()
...     BLUE = auto()
>>> EjectFlag(2**2 + 2**4)
20
KEEP

Out-of-range values are kept, and the Flag membership is kept. This is used for some stdlib flags:

>>> from enum import Flag, KEEP
>>> class KeepFlag(Flag, boundary=KEEP):
...     RED = auto()
...     GREEN = auto()
...     BLUE = auto()
>>> KeepFlag(2**2 + 2**4)
<KeepFlag.BLUE|16: 20>

3.11 新版功能.

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 to get an appropriate value for an enum member; may be overridden

    备注

    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.

3.6 新版功能: _missing_, _order_, _generate_next_value_

3.7 新版功能: _ignore_

Utilities and Decorators

class enum.auto

auto can be used in place of a value. If used, the Enum machinery will call an Enum’s _generate_next_value_() to get an appropriate value. For Enum and IntEnum that appropriate value will be the last value plus one; for Flag and IntFlag it will be the first power-of-two greater than the last value; for StrEnum it will be the lower-cased version of the member’s name.

_generate_next_value_ can be overridden to customize the values used by auto.

备注

in 3.13 the default "generate_next_value_ will always return the highest member value incremented by 1, and will fail if any member is an incompatible type.

@enum.property

A decorator similar to the built-in property, but specifically for enumerations. It allows member attributes to have the same names as members themselves.

备注

the property and the member must be defined in separate classes; for example, the value and name attributes are defined in the Enum class, and Enum subclasses can define members with the names value and name.

3.11 新版功能.

@enum.unique

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

>>> from enum import Enum, unique
>>> @unique
... class Mistake(Enum):
...     ONE = 1
...     TWO = 2
...     THREE = 3
...     FOUR = 3
...
Traceback (most recent call last):
...
ValueError: duplicate values found in <enum 'Mistake'>: FOUR -> THREE
@enum.verify

A class decorator specifically for enumerations. Members from EnumCheck are used to specify which constraints should be checked on the decorated enumeration.

3.11 新版功能.

@enum.member

A decorator for use in enums: its target will become a member.

3.11 新版功能.

@enum.nonmember

A decorator for use in enums: its target will not become a member.

3.11 新版功能.

Notes

IntEnum, StrEnum, and IntFlag

These three enum types are designed to be drop-in replacements for existing integer- and string-based values; as such, they have extra limitations:

  • __str__ uses the value and not the name of the enum member

  • __format__, because it uses __str__, will also use the value of the enum member instead of its name

If you do not need/want those limitations, you can either create your own base class by mixing in the int or str type yourself:

>>> from enum import Enum
>>> class MyIntEnum(int, Enum):
...     pass

or you can reassign the appropriate str(), etc., in your enum:

>>> from enum import IntEnum
>>> class MyIntEnum(IntEnum):
...     __str__ = IntEnum.__str__