`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.

EnumDict

A subclass of dict for use when subclassing EnumType.

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.

enum.bin()

Like built-in bin(), except negative values are represented in two’s complement, and the leading bit always indicates sign (0 implies positive, 1 implies negative).

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

Added in version 3.13: EnumDict

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.

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

__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 members 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>]

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).

The _order_ attribute can be provided to help keep Python 2 / Python 3 code in sync. 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']

Note

In Python 2 code the _order_ attribute is necessary as definition order is lost before it can be recorded.

Added in version 3.6.

_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.

Added in version 3.7.

__dir__(self)¶

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

>>> from enum import Enum
>>> import datetime as dt
>>> class Weekday(Enum):
...     MONDAY = 1
...     TUESDAY = 2
...     WEDNESDAY = 3
...     THURSDAY = 4
...     FRIDAY = 5
...     SATURDAY = 6
...     SUNDAY = 7
...     @classmethod
...     def today(cls):
...         print(f'today is {cls(dt.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.

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.

This method may be overridden, e.g.:

>>> from enum import auto, Enum
>>> 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

Added in version 3.6.

Changed in version 3.13: Prior versions would use the last seen value instead of the highest value.

__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 auto, 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'>

Added in version 3.6.

__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:

>>> from enum import auto, Enum
>>> 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:

>>> from enum import auto, Enum
>>> 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:

>>> from enum import auto, Enum
>>> 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.

_add_alias_()¶

Adds a new name as an alias to an existing member:

>>> Color.RED._add_alias_("ERROR")
>>> Color.ERROR
<Color.RED: 1>

Raises a NameError if the name is already assigned to a different member.

Added in version 3.13.

_add_value_alias_()¶

Adds a new value as an alias to an existing member:

>>> Color.RED._add_value_alias_(42)
>>> Color(42)
<Color.RED: 1>

Raises a ValueError if the value is already linked with a different member.

See MultiValueEnum for an example.

Added in version 3.13.

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.

>>> from enum import StrEnum, auto
>>> class Color(StrEnum):
...     RED = 'r'
...     GREEN = 'g'
...     BLUE = 'b'
...     UNKNOWN = auto()
...
>>> Color.RED
<Color.RED: 'r'>
>>> Color.UNKNOWN
<Color.UNKNOWN: 'unknown'>
>>> str(Color.UNKNOWN)
'unknown'

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(MyStrEnum.MY_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 | 

enum — Support for enumerations¶

Module contents¶

Data types¶

`enum` — Support for enumerations¶