enum — Support for enumerations

New in version 3.4.

Source code: 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 the 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 the class syntax to create Enums, Enums are not normal Python classes. See How are Enums different? for more details.

Note

Nomenclature

  • The class Color is an enumeration (or enum)

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

  • The enum members have names and values (the name of Color.RED is RED, the value of Color.BLUE is 3, etc.)


Module Contents

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

Base class for creating enumerated constants that can be combined using the bitwise operations without losing their Flag membership.

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.

global_enum()

Enum class decorator to apply the appropriate global __repr__, and export its members into the global name space.

property()

Allows Enum members to have attributes without conflicting with other members’ names.

unique()

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

verify()

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

New in version 3.6: Flag, IntFlag, auto

New in version 3.11: StrEnum, EnumCheck, FlagBoundary


Data Types

class enum.EnumType

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

__contains__(cls, member)

Returns True if member belongs to the cls:

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

Note

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. User-defined methods and methods from mixin classes will also be included:

>>> dir(Color)
['BLUE', 'GREEN', 'RED', '__class__', '__doc__', '__members__', '__module__']
__getattr__(cls, name)

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

>>> Color.GREEN
Color.GREEN
__getitem__(cls, name)

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

>>> Color['BLUE']
Color.BLUE
__iter__(cls)

Returns each member in cls in definition order:

>>> list(Color)
[Color.RED, Color.GREEN, Color.BLUE]
__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, Color.GREEN, Color.RED]
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

Note

Enum member values

Member values can be anything: int, str, etc.. If the exact value is unimportant you may use auto instances and an appropriate value will be chosen for you. Care must be taken if you mix auto with other values.

_ignore_

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

    value

    The value to lookup.

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

    cls

    The enum class being called.

    value

    The name of the new Enum to create.

    names

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

    module

    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

    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__ or a mixin 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__', '__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
_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
__repr__(self)

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

>>> class OldStyle(Enum):
...     RETRO = auto()
...     OLD_SCHOOl = auto()
...     YESTERYEAR = auto()
...     def __repr__(self):
...         cls_name = self.__class__.__name__
...         return f'<{cls_name}.{self.name}: {self.value}>'
>>> OldStyle.RETRO
<OldStyle.RETRO: 1>
__str__(self)

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

>>> class OldStyle(Enum):
...     RETRO = auto()
...     OLD_SCHOOl = auto()
...     YESTERYEAR = auto()
...     def __str__(self):
...         cls_name = self.__class__.__name__
...         return f'{cls_name}.{self.name}'
>>> OldStyle.RETRO
OldStyle.RETRO

Note

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
>>> Numbers.ONE + Numbers.TWO
3
>>> Numbers.THREE + 5
8
>>> Numbers.THREE == 3
True

Note

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

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.

Note

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).

Note

Using auto with StrEnum results in values of the member name, lower-cased.

New in version 3.11.

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]
>>> list(purple)
[Color.RED, Color.BLUE]
__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|Color.GREEN
__and__(self, other)

Returns current flag binary and’ed with other:

>>> purple & white
Color.RED|Color.BLUE
>>> purple & Color.GREEN
0x0
__xor__(self, other)

Returns current flag binary xor’ed with other:

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

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

>>> ~white
0x0
>>> ~purple
Color.GREEN
>>> ~Color.RED
Color.GREEN|Color.BLUE

Note

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

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
0x0
>>> Color.RED | 2
Color.RED|Color.GREEN

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

Note

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

class enum.EnumCheck

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

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]

Note

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

New in version 3.11.

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: 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
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|0x10

New in version 3.11.


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.

@enum.global_enum

A class decorator specifically for enumerations. It replaces the __repr__() method with one that shows module_name.*member_name*. It also injects the members, and their aliases, into the global namespace they were defined in.

New in version 3.11.

@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.

Note

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.

New in version 3.11.

@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.

New in version 3.11.


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:

  • format() will use the value of the enum member, unless __str__ has been overridden

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

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

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