# enum — Support for enumerations — Python 3.11.0a0 documentation

# `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`.

> `StrEnum`

> > Base class for creating enumerated constants that are also subclasses of `str`.

> `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`.

> `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.

New in version 3.6: `Flag`, `IntFlag`, `auto`

New in version 3.10: `StrEnum`

## 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:

        >>> 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__:

        >>> 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).naem)
        >>> 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.

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.``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

## Utilites 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 the global namespace they were defined in.

`@``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`.

`@``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