enum — Support for enumerations — Python 3.11.0 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 `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 `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.

> `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. Should only be used if the enum members will be exported to the module global namespace.

> `show_flag_values()`

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

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

New 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.

  __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__', '__contains__', '__doc__', '__getitem__', '__init_subclass__', '__iter__', '__len__', '__members__', '__module__', '__name__', '__qualname__']

  __getattr__(cls, name)

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

        >>> Color.GREEN
        <Color.GREEN: 2>

  __getitem__(cls, name)

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

  __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

    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 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.

  __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()).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 (count + 1) * 3
        ...     FIRST = auto()
        ...     SECOND = auto()
        >>> PowersOfThree.SECOND.value
        6

  __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'>

  __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__()` returns, 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`.

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: 3>
      >>> 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`.

  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.

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

  __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|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.

class enum.ReprEnum

  `ReprEum` 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() <str> / :func:`format` of the mixed-in data type instead of using the `Enum`-default `str()`.

  New 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.

  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: <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
        >>> 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`. 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|16: 20>

New 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

- `_name_` – name of the member

- `_value_` – value of the member; can be set / modified 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_` – used in Python 2/3 code to ensure member order is consistent (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 last value seen incremented by one.

  > For `Flag` classes the next value chosen will be the next highest power-of-two, regardless of the last value seen.

New in version 3.6: `_missing_`, `_order_`, `_generate_next_value_`

New in version 3.7: `_ignore_`

## 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.

  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`.

  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.

@enum.member

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

  New in version 3.11.

@enum.nonmember

  A decorator for use in enums: its target will not become a member.

  New 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).

  New in version 3.11.

enum.show_flag_values(value)

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

  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:

> > - `__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 IntEnum
>     >>> class MyIntEnum(IntEnum):
>     ...     __str__ = IntEnum.__str__