:mod:`enum` --- Support for enumerations
.. module:: enum :synopsis: Implementation of an enumeration class.
.. moduleauthor:: Ethan Furman <[email protected]>
.. sectionauthor:: Barry Warsaw <[email protected]>
.. sectionauthor:: Eli Bendersky <[email protected]>
.. sectionauthor:: Ethan Furman <[email protected]>
.. versionadded:: 3.4
Source code: :source:`Lib/enum.py`
Important
This page contains the API reference information. For tutorial information and discussion of more advanced topics, see
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 :keyword:`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 :keyword:`class` syntax to create Enums, Enums are not normal Python classes. See :ref:`How are Enums different? <enum-class-differences>` for more details.
Note
Nomenclature
- The class :class:`Color` is an enumeration (or enum)
- The attributes :attr:`Color.RED`, :attr:`Color.GREEN`, etc., are enumeration members (or members) and are functionally constants.
- The enum members have names and values (the name of
:attr:`Color.RED` is
RED, the value of :attr:`Color.BLUE` is3, etc.)
Thetypefor Enum and its subclasses.Base class for creating enumerated constants.Base class for creating enumerated constants that are also subclasses of :class:`int`. (Notes)Base class for creating enumerated constants that are also subclasses of :class:`str`. (Notes)Base class for creating enumerated constants that can be combined using the bitwise operations without losing their :class:`Flag` membership.Base class for creating enumerated constants that can be combined using the bitwise operators without losing their :class:`IntFlag` membership. :class:`IntFlag` members are also subclasses of :class:`int`. (Notes)An enumeration with the valuesCONTINUOUS,NAMED_FLAGS, andUNIQUE, for use with :func:`verify` to ensure various constraints are met by a given enumeration.An enumeration with the valuesSTRICT,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. :class:`StrEnum` defaults to the lower-cased version of the member name, while other Enums default to 1 and increase from there.Allows :class:`Enum` members to have attributes without conflicting with member names.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.
.. versionadded:: 3.6 ``Flag``, ``IntFlag``, ``auto``
.. versionadded:: 3.11 ``StrEnum``, ``EnumCheck``, ``FlagBoundary``, ``property``
EnumType is the :term:`metaclass` for enum enumerations. It is possible to subclass EnumType -- see :ref:`Subclassing EnumType <enumtype-examples>` for details.
EnumType is responsible for setting the correct :meth:`__repr__`, :meth:`__str__`, :meth:`__format__`, and :meth:`__reduce__` methods on the final enum, as well as creating the enum members, properly handling duplicates, providing iteration over the enum class, etc.
.. method:: EnumType.__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.
.. method:: EnumType.__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__']
.. method:: EnumType.__getattr__(cls, name)
Returns the Enum member in *cls* matching *name*, or raises an :exc:`AttributeError`::
>>> Color.GREEN
<Color.GREEN: 2>
.. method:: EnumType.__getitem__(cls, name)
Returns the Enum member in *cls* matching *name*, or raises an :exc:`KeyError`::
>>> Color['BLUE']
<Color.BLUE: 3>
.. method:: EnumType.__iter__(cls)
Returns each member in *cls* in definition order::
>>> list(Color)
[<Color.RED: 1>, <Color.GREEN: 2>, <Color.BLUE: 3>]
.. method:: EnumType.__len__(cls)
Returns the number of member in *cls*::
>>> len(Color)
3
.. method:: EnumType.__reversed__(cls)
Returns each member in *cls* in reverse definition order::
>>> list(reversed(Color))
[<Color.BLUE: 3>, <Color.GREEN: 2>, <Color.RED: 1>]
Enum is the base class for all enum enumerations.
.. attribute:: Enum.name
The name used to define the ``Enum`` member::
>>> Color.BLUE.name
'BLUE'
.. attribute:: Enum.value
The value given to the ``Enum`` member::
>>> Color.RED.value
1
.. note:: Enum member values
Member values can be anything: :class:`int`, :class:`str`, etc.. If
the exact value is unimportant you may use :class:`auto` instances and an
appropriate value will be chosen for you. Care must be taken if you mix
:class:`auto` with other values.
.. attribute:: Enum._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 :ref:`TimePeriod <enum-time-period>` for an example.
.. method:: Enum.__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 :class:`auto`)
:boundary: How to handle out-of-range values from bit operations (:class:`Flag` only)
.. method:: Enum.__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']
.. method:: Enum._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
:class:`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
.. method:: Enum.__init_subclass__(cls, \**kwds) A *classmethod* that is used to further configure subsequent subclasses. By default, does nothing.
.. method:: Enum._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'>
.. method:: Enum.__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')
.. method:: Enum.__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')
.. method:: Enum.__format__(self)
Returns the string used for *format()* and *f-string* calls. By default,
returns :meth:`__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 :class:`auto` with :class:`Enum` results in integers of increasing value,
starting with 1.
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 :class:`auto` with :class:`IntEnum` results in integers of increasing
value, starting with 1.
.. versionchanged:: 3.11 :meth:`__str__` is now :func:`int.__str__` to better support the *replacement of existing constants* use-case. :meth:`__format__` was already :func:`int.__format__` for that same reason.
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 :class:`str`
instead of a :class:`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 :class:`auto` with :class:`StrEnum` results in the lower-cased member name as the value.
Note
:meth:`__str__` is :func:`str.__str__` to better support the replacement of existing constants use-case. :meth:`__format__` is likewise :func:`int.__format__` for that same reason.
.. versionadded:: 3.11
Flag members support the bitwise operators & (AND), | (OR),
^ (XOR), and ~ (INVERT); the results of those operators are members
of the enumeration.
.. method:: __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
.. method:: __iter__(self):
Returns all contained members::
>>> list(Color.RED)
[<Color.RED: 1>]
>>> list(purple)
[<Color.RED: 1>, <Color.BLUE: 4>]
.. method:: __len__(self):
Returns number of members in flag::
>>> len(Color.GREEN)
1
>>> len(white)
3
.. method:: __bool__(self):
Returns *True* if any members in flag, *False* otherwise::
>>> bool(Color.GREEN)
True
>>> bool(white)
True
>>> black = Color(0)
>>> bool(black)
False
.. method:: __or__(self, other)
Returns current flag binary or'ed with other::
>>> Color.RED | Color.GREEN
<Color.RED|GREEN: 3>
.. method:: __and__(self, other)
Returns current flag binary and'ed with other::
>>> purple & white
<Color.RED|BLUE: 5>
>>> purple & Color.GREEN
<Color: 0>
.. method:: __xor__(self, other)
Returns current flag binary xor'ed with other::
>>> purple ^ white
<Color.GREEN: 2>
>>> purple ^ Color.GREEN
<Color.RED|GREEN|BLUE: 7>
.. method:: __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>
.. method:: _numeric_repr_ Function used to format any remaining unnamed numeric values. Default is the value's repr; common choices are :func:`hex` and :func:`oct`.
Note
Using :class:`auto` with :class:`Flag` results in integers that are powers
of two, starting with 1.
.. versionchanged:: 3.11 The *repr()* of zero-valued flags has changed. It
is now::
>>> Color(0)
<Color: 0>
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 :class:`auto` with :class:`IntFlag` results in integers that are powers
of two, starting with 1.
.. versionchanged:: 3.11 :meth:`__str__` is now :func:`int.__str__` to better support the *replacement of existing constants* use-case. :meth:`__format__` was already :func:`int.__format__` for that same reason.
EnumCheck contains the options used by the :func:`verify` decorator to ensure various constraints; failed constraints result in a :exc:`ValueError`.
.. attribute:: 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
.. attribute:: 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
.. attribute:: NAMED_FLAGS
Ensure that any flag groups/masks contain only named flags -- useful when
values are specified instead of being generated by :func:`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.
.. versionadded:: 3.11
FlagBoundary controls how out-of-range values are handled in Flag and its subclasses.
.. attribute:: STRICT
Out-of-range values cause a :exc:`ValueError` to be raised. This is the
default for :class:`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
.. attribute:: 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>
.. attribute:: EJECT
Out-of-range values lose their *Flag* membership and revert to :class:`int`.
This is the default for :class:`IntFlag`::
>>> from enum import Flag, EJECT
>>> class EjectFlag(Flag, boundary=EJECT):
... RED = auto()
... GREEN = auto()
... BLUE = auto()
>>> EjectFlag(2**2 + 2**4)
20
.. attribute:: 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>
.. versionadded:: 3.11
:attr:`__members__` is a read-only ordered mapping of member_name:member
items. It is only available on the class.
:meth:`__new__`, if specified, must create and return the enum members; it is also a very good idea to set the member's :attr:`_value_` appropriately. Once all the members are created it is no longer used.
_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 :class:`list` or a :class:`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 overriddenNote
For standard :class:`Enum` classes the next value chosen is the last value seen incremented by one.
For :class:`Flag` classes the next value chosen will be the next highest power-of-two, regardless of the last value seen.
.. versionadded:: 3.6 ``_missing_``, ``_order_``, ``_generate_next_value_``
.. versionadded:: 3.7 ``_ignore_``
auto can be used in place of a value. If used, the Enum machinery will call an Enum's :meth:`_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.
.. decorator:: 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``.
.. versionadded:: 3.11
.. decorator:: unique
A :keyword:`class` decorator specifically for enumerations. It searches an
enumeration's :attr:`__members__`, gathering any aliases it finds; if any are
found :exc:`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
.. decorator:: verify A :keyword:`class` decorator specifically for enumerations. Members from :class:`EnumCheck` are used to specify which constraints should be checked on the decorated enumeration. .. versionadded:: 3.11
:class:`IntEnum`, :class:`StrEnum`, and :class:`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 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 :meth:`str`, etc., in your enum:
>>> from enum import IntEnum >>> class MyIntEnum(IntEnum): ... __str__ = IntEnum.__str__