"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 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

   __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 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 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
