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', '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.
Note
Nomenclature
- The class - Coloris 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.REDis- RED, the value of- Color.BLUEis- 3, etc.)
Module Contents¶
The
typefor Enum and its subclasses.Base class for creating enumerated constants.
Base class for creating enumerated constants that can be combined using the bitwise operations without losing their
Flagmembership.An enumeration with the values
CONTINUOUS,NAMED_FLAGS, andUNIQUE, for use withverify()to ensure various constraints are met by a given enumeration.An enumeration with the values
STRICT,CONFORM,EJECT, andKEEPwhich allows for more fine-grained control over how invalid values are dealt with in an enumeration.Instances are replaced with an appropriate value for Enum members.
StrEnumdefaults to the lower-cased version of the member name, while other Enums default to 1 and increase from there.Allows
Enummembers to have attributes without conflicting with member names. Thevalueandnameattributes are implemented this way.Enum class decorator that ensures only one name is bound to any one value.
Enum class decorator that checks user-selectable constraints on an enumeration.
Make
obja member. Can be used as a decorator.Do not make
obja member. Can be used as a decorator.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. - EnumTypeis 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 - clsenum 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 ( - Flagonly).
 
 
 - __contains__(cls, member)¶
- Returns - Trueif 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 - TypeErroris 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 - NameErrorif 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 - ValueErrorif the value is already linked with a different member.
 - Added in version 3.11: Before 3.11 - EnumTypewas 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 - Enummember:- >>> Color.BLUE.name 'BLUE' 
 - value¶
- The value given to the - Enummember:- >>> 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- autoinstances and an appropriate value will be chosen for you. See- autofor the details.- While mutable/unhashable values, such as - dict,- listor 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. 
 - _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- 26for 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') 
 - 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 - 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¶
- StrEnumis 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 - strinstead of a- strsubclass (i.e.- type(unknown) == strinstead of- isinstance(unknown, str)), and in those locations you will need to use- str(StrEnum.member).- 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¶
- Flagis 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().
 - Changed in version 3.11: The repr() of zero-valued flags has changed. It is now:: - >>> Color(0) <Color: 0> 
- class enum.IntFlag¶
- IntFlagis 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 - Flagoperation 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 - FlagBoundarysetting
 - The - repr()of unnamed zero-valued flags has changed. It is now:- >>> Color(0) <Color: 0> - 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 - IntFlagnow 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- Flagbehavior.
- class enum.ReprEnum¶
- ReprEnumuses the- repr()of- Enum, but the- str()of the mixed-in data type:- Inherit from - ReprEnumto 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¶
- FlagBoundarycontrols how out-of-range values are handled in- Flagand its subclasses.- STRICT¶
- Out-of-range values cause a - ValueErrorto 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 - Flagvalue:- >>> 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> 
 
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- listor 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
- While - _sunder_names are generally reserved for the further development of the- Enumclass 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- Enumand- IntEnumthat appropriate value will be the last value plus one; for- Flagand- IntFlagit will be the first power-of-two greater than the highest value; for- StrEnumit 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(), -2will work (auto is replaced with- 2, so- 2, -2is used to create the- SECONDenum member;
- THREE = [auto(), -3]will not work (- <auto instance>, -3is used to create the- THREEenum 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 - valueand- name.- Added in version 3.11. 
- @enum.unique¶
- A - classdecorator specifically for enumerations. It searches an enumeration’s- __members__, gathering any aliases it finds; if any are found- ValueErroris 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 - classdecorator specifically for enumerations. Members from- EnumCheckare 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.RegexFlagfor 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¶
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 nameIf you do not need/want those limitations, you can either create your own base class by mixing in the
intorstrtype yourself:>>> from enum import Enum >>> class MyIntEnum(int, Enum): ... passor you can reassign the appropriate
str(), etc., in your enum:>>> from enum import Enum, IntEnum >>> class MyIntEnum(IntEnum): ... __str__ = Enum.__str__