`enum` — Support for enumerations¶

Added 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 canonical (i.e. non-alias) 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', 1), ('GREEN', 2), ('BLUE', 3)])

Even though we can use 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 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)

ReprEnum

Used by IntEnum, StrEnum, and IntFlag to keep the str() of the mixed-in type.

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. The value and name attributes are implemented this way.

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.

member()

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

nonmember()

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

global_enum()

Modify the str() and repr() of an enum to show its members as belonging to the module instead of its class, and export the enum members to the global namespace.

show_flag_values()

Return a list of all power-of-two integers contained in a flag.

Added in version 3.6: Flag, IntFlag, auto

Added in version 3.11: StrEnum, EnumCheck, ReprEnum, FlagBoundary, property, member, nonmember, global_enum, show_flag_values

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.

__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 (only if the existing enum does not have any members):

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).

__contains__(cls, member)¶

Returns True if member belongs to the cls:

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

Changed in version 3.12: Before Python 3.12, a TypeError is 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 a 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

__members__¶: Returns a mapping of every enum name to its member, including aliases

__reversed__(cls)¶

Returns each member in cls in reverse definition order:

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

_add_alias_()¶: Adds a new name as an alias to an existing member. Raises a NameError if the name is already assigned to a different member.

_add_value_alias_()¶: Adds a new value as an alias to an existing member. Raises a ValueError if the value is already linked with a different member.

Added in version 3.11: Before 3.11 EnumType was called EnumMeta, which is still available as an alias.

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

Value of the member, can be set in __new__().

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. See auto for the details.

While mutable/unhashable values, such as dict, list or a mutable dataclass, can be used, they will have a quadratic performance impact during creation relative to the total number of mutable/unhashable values in the enum.

_name_¶: Name of the member.

_value_¶: Value of the member, can be set in __new__().

_order_¶: No longer used, kept for backward compatibility. (class attribute, removed during class creation).

_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.

__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 3 ** (count + 1)
...     FIRST = auto()
...     SECOND = auto()
...
>>> PowersOfThree.SECOND.value
9

__init__(self, *args, **kwds)¶

By default, does nothing. If multiple values are given in the member assignment, those values become separate arguments to __init__; e.g.

>>> from enum import Enum
>>> class Weekday(Enum):
...     MONDAY = 1, 'Mon'

Weekday.__init__() would be called as Weekday.__init__(self, 1, 'Mon')

__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'>

__new__(cls, *args, **kwds)¶

By default, doesn’t exist. If specified, either in the enum class definition or in a mixin class (such as int), all values given in the member assignment will be passed; e.g.

>>> from enum import Enum
>>> class MyIntEnum(int, Enum):
...     TWENTYSIX = '1a', 16

results in the call int('1a', 16) and a value of 26 for the member.

Note

When writing a custom __new__, do not use super().__new__ – call the appropriate __new__ instead.

__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__() return value, 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')

Note

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

Changed in version 3.12: Added Dataclass support

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 Number(IntEnum):
...     ONE = 1
...     TWO = 2
...     THREE = 3
...
>>> Number.THREE
<Number.THREE: 3>
>>> Number.ONE + Number.TWO
3
>>> Number.THREE + 5
8
>>> Number.THREE == 3
True

Note

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

Changed in version 3.11: __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.

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(unknown, str)), and in those locations you will need to use str(StrEnum.member).

Note

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

Note

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

Added in version 3.11.

class enum.Flag¶

Flag is the same as Enum, but its members support the bitwise operators & (AND), | (OR), ^ (XOR), and ~ (INVERT); the results of those operations are (aliases of) 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 non-alias members:

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

Added in version 3.11.

__len__(self):

Returns number of members in flag:

>>> len(Color.GREEN)
1
>>> len(white)
3

Added in version 3.11.

__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().

Note

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

Changed in version 3.11: 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>

Note

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

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

Inversion of an IntFlag now returns a positive value that is the union of all flags not in the given flag, rather than a negative value. This matches the existing Flag behavior.

class enum.ReprEnum¶

ReprEnum uses the repr() of Enum, but the str() of the mixed-in data type:

int.__str__() for IntEnum and IntFlag
str.__str__() for StrEnum

Inherit from ReprEnum to keep the str() / format() of the mixed-in data type instead of using the Enum-default str().

Added in version 3.11.

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]

Note

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

Added 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, auto
>>> 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, auto
>>> 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.

>>> from enum import Flag, EJECT, auto
>>> 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 the default for IntFlag:

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

Added in version 3.11.

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¶

_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.
_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
_order_ – no longer used, kept for backward compatibility (class attribute, removed during class creation)
_generate_next_value_() – used to get an appropriate value for an enum member; may be overridden

Note

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.
While _sunder_ names are generally reserved for the further development of the Enum class and can not be used, some are explicitly allowed:
- _repr_* (e.g. _repr_html_), as used in IPython’s rich display

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_, _repr_*

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 highest value; for StrEnum it will be the lower-cased version of the member’s name. Care must be taken if mixing auto() with manually specified values.

auto instances are only resolved when at the top level of an assignment:

FIRST = auto() will work (auto() is replaced with 1);
SECOND = auto(), -2 will work (auto is replaced with 2, so 2, -2 is used to create the SECOND enum member;
THREE = [auto(), -3] will not work (<auto instance>, -3 is used to create the THREE enum member)

Changed in version 3.11.1: In prior versions, auto() had to be the only thing on the assignment line to work properly.

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

Note

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.

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.

Added 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.

Added in version 3.11.

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

Added in version 3.11.

@enum.nonmember¶: A decorator for use in enums: its target will not become a member.

Added in version 3.11.

@enum.global_enum¶: A decorator to change the str() and repr() of an enum to show its members as belonging to the module instead of its class. Should only be used when the enum members are exported to the module global namespace (see re.RegexFlag for an example).

Added in version 3.11.

enum.show_flag_values(value)¶: Return a list of all power-of-two integers contained in a flag value.

Added 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:

__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 Enum, IntEnum
>>> class MyIntEnum(IntEnum):
...     __str__ = Enum.__str__

`enum` — Support for enumerations¶

Module Contents¶

Data Types¶

Supported `dunder` names¶

Supported `_sunder_` names¶

Utilities and Decorators¶

Notes¶

Table of Contents

Previous topic

Next topic

This Page

enum — Support for enumerations¶

Module Contents¶

Data Types¶

Supported __dunder__ names¶

Supported _sunder_ names¶

Utilities and Decorators¶

Notes¶

`enum` — Support for enumerations¶

Supported `dunder` names¶

Supported `_sunder_` names¶