"enum" --- Support for enumerations
***********************************

New in version 3.4.

**Source code:** Lib/enum.py


Important
^^^^^^^^^

This page contains the API reference information. For tutorial
information and discussion of more advanced topics, see

* Basic Tutorial

* Advanced Tutorial

* Enum Cookbook

======================================================================

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)

   "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.

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

New in version 3.11: "StrEnum", "EnumCheck", "FlagBoundary",
"property"

New in version 3.11: "member", "nonmember"

======================================================================


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 valuesMember 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(str, unknown)"), 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.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.

======================================================================


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__
