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-``enum`` --- support for enumerations
-========================================
-
-.. :synopsis: enumerations are sets of symbolic names bound to unique, constant
- values.
-.. :moduleauthor:: Ethan Furman <ethan@stoneleaf.us>
-.. :sectionauthor:: Barry Warsaw <barry@python.org>,
-.. :sectionauthor:: Eli Bendersky <eliben@gmail.com>,
-.. :sectionauthor:: Ethan Furman <ethan@stoneleaf.us>
-
-----------------
-
-An enumeration is a set of symbolic names (members) bound to unique, constant
-values. Within an enumeration, the members can be compared by identity, and
-the enumeration itself can be iterated over.
-
-
-Module Contents
----------------
-
-This module defines two enumeration classes that can be used to define unique
-sets of names and values: ``Enum`` and ``IntEnum``. It also defines
-one decorator, ``unique``.
-
-``Enum``
-
-Base class for creating enumerated constants. See section `Functional API`_
-for an alternate construction syntax.
-
-``IntEnum``
-
-Base class for creating enumerated constants that are also subclasses of ``int``.
-
-``unique``
-
-Enum class decorator that ensures only one name is bound to any one value.
-
-
-Creating an Enum
-----------------
-
-Enumerations are created using the ``class`` syntax, which makes them
-easy to read and write. An alternative creation method is described in
-`Functional API`_. To define an enumeration, subclass ``Enum`` as
-follows::
-
- >>> from enum import Enum
- >>> class Color(Enum):
- ... red = 1
- ... green = 2
- ... blue = 3
-
-Note: Nomenclature
-
- - The class ``Color`` is an *enumeration* (or *enum*)
- - The attributes ``Color.red``, ``Color.green``, etc., are
- *enumeration members* (or *enum members*).
- - The enum members have *names* and *values* (the name of
- ``Color.red`` is ``red``, the value of ``Color.blue`` is
- ``3``, etc.)
-
-Note:
-
- Even though we use the ``class`` syntax to create Enums, Enums
- are not normal Python classes. See `How are Enums different?`_ for
- more details.
-
-Enumeration members have human readable string representations::
-
- >>> print(Color.red)
- Color.red
-
-...while their ``repr`` has more information::
-
- >>> print(repr(Color.red))
- <Color.red: 1>
-
-The *type* of an enumeration member is the enumeration it belongs to::
-
- >>> type(Color.red)
- <enum 'Color'>
- >>> isinstance(Color.green, Color)
- True
- >>>
-
-Enum members also have a property that contains just their item name::
-
- >>> print(Color.red.name)
- red
-
-Enumerations support iteration. In Python 3.x definition order is used; in
-Python 2.x the definition order is not available, but class attribute
-``__order__`` is supported; otherwise, value order is used::
-
- >>> class Shake(Enum):
- ... __order__ = 'vanilla chocolate cookies mint' # only needed in 2.x
- ... vanilla = 7
- ... chocolate = 4
- ... cookies = 9
- ... mint = 3
- ...
- >>> for shake in Shake:
- ... print(shake)
- ...
- Shake.vanilla
- Shake.chocolate
- Shake.cookies
- Shake.mint
-
-The ``__order__`` attribute is always removed, and in 3.x it is also ignored
-(order is definition order); however, in the stdlib version it will be ignored
-but not removed.
-
-Enumeration members are hashable, so they can be used in dictionaries and sets::
-
- >>> apples = {}
- >>> apples[Color.red] = 'red delicious'
- >>> apples[Color.green] = 'granny smith'
- >>> apples == {Color.red: 'red delicious', Color.green: 'granny smith'}
- True
-
-
-Programmatic access to enumeration members and their attributes
----------------------------------------------------------------
-
-Sometimes it's useful to access members in enumerations programmatically (i.e.
-situations where ``Color.red`` won't do because the exact color is not known
-at program-writing time). ``Enum`` allows such access::
-
- >>> Color(1)
- <Color.red: 1>
- >>> Color(3)
- <Color.blue: 3>
-
-If you want to access enum members by *name*, use item access::
-
- >>> Color['red']
- <Color.red: 1>
- >>> Color['green']
- <Color.green: 2>
-
-If have an enum member and need its ``name`` or ``value``::
-
- >>> member = Color.red
- >>> member.name
- 'red'
- >>> member.value
- 1
-
-
-Duplicating enum members and values
------------------------------------
-
-Having two enum members (or any other attribute) with the same name is invalid;
-in Python 3.x this would raise an error, but in Python 2.x the second member
-simply overwrites the first::
-
- >>> # python 2.x
- >>> class Shape(Enum):
- ... square = 2
- ... square = 3
- ...
- >>> Shape.square
- <Shape.square: 3>
-
- >>> # python 3.x
- >>> class Shape(Enum):
- ... square = 2
- ... square = 3
- Traceback (most recent call last):
- ...
- TypeError: Attempted to reuse key: 'square'
-
-However, two enum members are allowed to have the same value. Given two members
-A and B with the same value (and A defined first), B is an alias to A. By-value
-lookup of the value of A and B will return A. By-name lookup of B will also
-return A::
-
- >>> class Shape(Enum):
- ... __order__ = 'square diamond circle alias_for_square' # only needed in 2.x
- ... square = 2
- ... diamond = 1
- ... circle = 3
- ... alias_for_square = 2
- ...
- >>> Shape.square
- <Shape.square: 2>
- >>> Shape.alias_for_square
- <Shape.square: 2>
- >>> Shape(2)
- <Shape.square: 2>
-
-
-Allowing aliases is not always desirable. ``unique`` can be used to ensure
-that none exist in a particular enumeration::
-
- >>> from enum import unique
- >>> @unique
- ... class Mistake(Enum):
- ... __order__ = 'one two three four' # only needed in 2.x
- ... one = 1
- ... two = 2
- ... three = 3
- ... four = 3
- Traceback (most recent call last):
- ...
- ValueError: duplicate names found in <enum 'Mistake'>: four -> three
-
-Iterating over the members of an enum does not provide the aliases::
-
- >>> list(Shape)
- [<Shape.square: 2>, <Shape.diamond: 1>, <Shape.circle: 3>]
-
-The special attribute ``__members__`` is a dictionary mapping names to members.
-It includes all names defined in the enumeration, including the aliases::
-
- >>> for name, member in sorted(Shape.__members__.items()):
- ... name, member
- ...
- ('alias_for_square', <Shape.square: 2>)
- ('circle', <Shape.circle: 3>)
- ('diamond', <Shape.diamond: 1>)
- ('square', <Shape.square: 2>)
-
-The ``__members__`` attribute can be used for detailed programmatic access to
-the enumeration members. For example, finding all the aliases::
-
- >>> [name for name, member in Shape.__members__.items() if member.name != name]
- ['alias_for_square']
-
-Comparisons
------------
-
-Enumeration members are compared by identity::
-
- >>> Color.red is Color.red
- True
- >>> Color.red is Color.blue
- False
- >>> Color.red is not Color.blue
- True
-
-Ordered comparisons between enumeration values are *not* supported. Enum
-members are not integers (but see `IntEnum`_ below)::
-
- >>> Color.red < Color.blue
- Traceback (most recent call last):
- File "<stdin>", line 1, in <module>
- TypeError: unorderable types: Color() < Color()
-
-.. warning::
-
- In Python 2 *everything* is ordered, even though the ordering may not
- make sense. If you want your enumerations to have a sensible ordering
- check out the `OrderedEnum`_ recipe below.
-
-
-Equality comparisons are defined though::
-
- >>> Color.blue == Color.red
- False
- >>> Color.blue != Color.red
- True
- >>> Color.blue == Color.blue
- True
-
-Comparisons against non-enumeration values will always compare not equal
-(again, ``IntEnum`` was explicitly designed to behave differently, see
-below)::
-
- >>> Color.blue == 2
- False
-
-
-Allowed members and attributes of enumerations
-----------------------------------------------
-
-The examples above use integers for enumeration values. Using integers is
-short and handy (and provided by default by the `Functional API`_), but not
-strictly enforced. In the vast majority of use-cases, one doesn't care what
-the actual value of an enumeration is. But if the value *is* important,
-enumerations can have arbitrary values.
-
-Enumerations are Python classes, and can have methods and special methods as
-usual. If we have this enumeration::
-
- >>> class Mood(Enum):
- ... funky = 1
- ... happy = 3
- ...
- ... def describe(self):
- ... # self is the member here
- ... return self.name, self.value
- ...
- ... def __str__(self):
- ... return 'my custom str! {0}'.format(self.value)
- ...
- ... @classmethod
- ... def favorite_mood(cls):
- ... # cls here is the enumeration
- ... return cls.happy
-
-Then::
-
- >>> Mood.favorite_mood()
- <Mood.happy: 3>
- >>> Mood.happy.describe()
- ('happy', 3)
- >>> str(Mood.funky)
- 'my custom str! 1'
-
-The rules for what is allowed are as follows: _sunder_ names (starting and
-ending with a single underscore) are reserved by enum and cannot be used;
-all other attributes defined within an enumeration will become members of this
-enumeration, with the exception of *__dunder__* names and descriptors (methods
-are also descriptors).
-
-Note:
-
- If your enumeration defines ``__new__`` and/or ``__init__`` then
- whatever value(s) were given to the enum member will be passed into
- those methods. See `Planet`_ for an example.
-
-
-Restricted subclassing of enumerations
---------------------------------------
-
-Subclassing an enumeration is allowed only if the enumeration does not define
-any members. So this is forbidden::
-
- >>> class MoreColor(Color):
- ... pink = 17
- Traceback (most recent call last):
- ...
- TypeError: Cannot extend enumerations
-
-But this is allowed::
-
- >>> class Foo(Enum):
- ... def some_behavior(self):
- ... pass
- ...
- >>> class Bar(Foo):
- ... happy = 1
- ... sad = 2
- ...
-
-Allowing subclassing of enums that define members would lead to a violation of
-some important invariants of types and instances. On the other hand, it makes
-sense to allow sharing some common behavior between a group of enumerations.
-(See `OrderedEnum`_ for an example.)
-
-
-Pickling
---------
-
-Enumerations can be pickled and unpickled::
-
- >>> from enum.test_enum import Fruit
- >>> from pickle import dumps, loads
- >>> Fruit.tomato is loads(dumps(Fruit.tomato, 2))
- True
-
-The usual restrictions for pickling apply: picklable enums must be defined in
-the top level of a module, since unpickling requires them to be importable
-from that module.
-
-Note:
-
- With pickle protocol version 4 (introduced in Python 3.4) it is possible
- to easily pickle enums nested in other classes.
-
-
-
-Functional API
---------------
-
-The ``Enum`` class is callable, providing the following functional API::
-
- >>> Animal = Enum('Animal', 'ant bee cat dog')
- >>> Animal
- <enum 'Animal'>
- >>> Animal.ant
- <Animal.ant: 1>
- >>> Animal.ant.value
- 1
- >>> list(Animal)
- [<Animal.ant: 1>, <Animal.bee: 2>, <Animal.cat: 3>, <Animal.dog: 4>]
-
-The semantics of this API resemble ``namedtuple``. The first argument
-of the call to ``Enum`` is the name of the enumeration.
-
-The second argument is the *source* of enumeration member names. It can be a
-whitespace-separated string of names, a sequence of names, a sequence of
-2-tuples with key/value pairs, or a mapping (e.g. dictionary) of names to
-values. The last two options enable assigning arbitrary values to
-enumerations; the others auto-assign increasing integers starting with 1. A
-new class derived from ``Enum`` is returned. In other words, the above
-assignment to ``Animal`` is equivalent to::
-
- >>> class Animals(Enum):
- ... ant = 1
- ... bee = 2
- ... cat = 3
- ... dog = 4
-
-Pickling enums created with the functional API can be tricky as frame stack
-implementation details are used to try and figure out which module the
-enumeration is being created in (e.g. it will fail if you use a utility
-function in separate module, and also may not work on IronPython or Jython).
-The solution is to specify the module name explicitly as follows::
-
- >>> Animals = Enum('Animals', 'ant bee cat dog', module=__name__)
-
-Derived Enumerations
---------------------
-
-IntEnum
-^^^^^^^
-
-A variation of ``Enum`` is provided which is also a subclass of
-``int``. Members of an ``IntEnum`` can be compared to integers;
-by extension, integer enumerations of different types can also be compared
-to each other::
-
- >>> from enum import IntEnum
- >>> class Shape(IntEnum):
- ... circle = 1
- ... square = 2
- ...
- >>> class Request(IntEnum):
- ... post = 1
- ... get = 2
- ...
- >>> Shape == 1
- False
- >>> Shape.circle == 1
- True
- >>> Shape.circle == Request.post
- True
-
-However, they still can't be compared to standard ``Enum`` enumerations::
-
- >>> class Shape(IntEnum):
- ... circle = 1
- ... square = 2
- ...
- >>> class Color(Enum):
- ... red = 1
- ... green = 2
- ...
- >>> Shape.circle == Color.red
- False
-
-``IntEnum`` values behave like integers in other ways you'd expect::
-
- >>> int(Shape.circle)
- 1
- >>> ['a', 'b', 'c'][Shape.circle]
- 'b'
- >>> [i for i in range(Shape.square)]
- [0, 1]
-
-For the vast majority of code, ``Enum`` is strongly recommended,
-since ``IntEnum`` breaks some semantic promises of an enumeration (by
-being comparable to integers, and thus by transitivity to other
-unrelated enumerations). It should be used only in special cases where
-there's no other choice; for example, when integer constants are
-replaced with enumerations and backwards compatibility is required with code
-that still expects integers.
-
-
-Others
-^^^^^^
-
-While ``IntEnum`` is part of the ``enum`` module, it would be very
-simple to implement independently::
-
- class IntEnum(int, Enum):
- pass
-
-This demonstrates how similar derived enumerations can be defined; for example
-a ``StrEnum`` that mixes in ``str`` instead of ``int``.
-
-Some rules:
-
-1. When subclassing ``Enum``, mix-in types must appear before
- ``Enum`` itself in the sequence of bases, as in the ``IntEnum``
- example above.
-2. While ``Enum`` can have members of any type, once you mix in an
- additional type, all the members must have values of that type, e.g.
- ``int`` above. This restriction does not apply to mix-ins which only
- add methods and don't specify another data type such as ``int`` or
- ``str``.
-3. When another data type is mixed in, the ``value`` attribute is *not the
- same* as the enum member itself, although it is equivalant and will compare
- equal.
-4. %-style formatting: ``%s`` and ``%r`` call ``Enum``'s ``__str__`` and
- ``__repr__`` respectively; other codes (such as ``%i`` or ``%h`` for
- IntEnum) treat the enum member as its mixed-in type.
-
- Note: Prior to Python 3.4 there is a bug in ``str``'s %-formatting: ``int``
- subclasses are printed as strings and not numbers when the ``%d``, ``%i``,
- or ``%u`` codes are used.
-5. ``str.__format__`` (or ``format``) will use the mixed-in
- type's ``__format__``. If the ``Enum``'s ``str`` or
- ``repr`` is desired use the ``!s`` or ``!r`` ``str`` format codes.
-
-
-Decorators
-----------
-
-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::
-
- >>> @unique
- ... class NoDupes(Enum):
- ... first = 'one'
- ... second = 'two'
- ... third = 'two'
- Traceback (most recent call last):
- ...
- ValueError: duplicate names found in <enum 'NoDupes'>: third -> second
-
-
-Interesting examples
---------------------
-
-While ``Enum`` and ``IntEnum`` are expected to cover the majority of
-use-cases, they cannot cover them all. Here are recipes for some different
-types of enumerations that can be used directly, or as examples for creating
-one's own.
-
-
-AutoNumber
-^^^^^^^^^^
-
-Avoids having to specify the value for each enumeration member::
-
- >>> class AutoNumber(Enum):
- ... def __new__(cls):
- ... value = len(cls.__members__) + 1
- ... obj = object.__new__(cls)
- ... obj._value_ = value
- ... return obj
- ...
- >>> class Color(AutoNumber):
- ... __order__ = "red green blue" # only needed in 2.x
- ... red = ()
- ... green = ()
- ... blue = ()
- ...
- >>> Color.green.value == 2
- True
-
-Note:
-
- The `__new__` method, if defined, is used during creation of the Enum
- members; it is then replaced by Enum's `__new__` which is used after
- class creation for lookup of existing members. Due to the way Enums are
- supposed to behave, there is no way to customize Enum's `__new__`.
-
-
-UniqueEnum
-^^^^^^^^^^
-
-Raises an error if a duplicate member name is found instead of creating an
-alias::
-
- >>> class UniqueEnum(Enum):
- ... def __init__(self, *args):
- ... cls = self.__class__
- ... if any(self.value == e.value for e in cls):
- ... a = self.name
- ... e = cls(self.value).name
- ... raise ValueError(
- ... "aliases not allowed in UniqueEnum: %r --> %r"
- ... % (a, e))
- ...
- >>> class Color(UniqueEnum):
- ... red = 1
- ... green = 2
- ... blue = 3
- ... grene = 2
- Traceback (most recent call last):
- ...
- ValueError: aliases not allowed in UniqueEnum: 'grene' --> 'green'
-
-
-OrderedEnum
-^^^^^^^^^^^
-
-An ordered enumeration that is not based on ``IntEnum`` and so maintains
-the normal ``Enum`` invariants (such as not being comparable to other
-enumerations)::
-
- >>> class OrderedEnum(Enum):
- ... def __ge__(self, other):
- ... if self.__class__ is other.__class__:
- ... return self._value_ >= other._value_
- ... return NotImplemented
- ... def __gt__(self, other):
- ... if self.__class__ is other.__class__:
- ... return self._value_ > other._value_
- ... return NotImplemented
- ... def __le__(self, other):
- ... if self.__class__ is other.__class__:
- ... return self._value_ <= other._value_
- ... return NotImplemented
- ... def __lt__(self, other):
- ... if self.__class__ is other.__class__:
- ... return self._value_ < other._value_
- ... return NotImplemented
- ...
- >>> class Grade(OrderedEnum):
- ... __ordered__ = 'A B C D F'
- ... A = 5
- ... B = 4
- ... C = 3
- ... D = 2
- ... F = 1
- ...
- >>> Grade.C < Grade.A
- True
-
-
-Planet
-^^^^^^
-
-If ``__new__`` or ``__init__`` is defined the value of the enum member
-will be passed to those methods::
-
- >>> class Planet(Enum):
- ... MERCURY = (3.303e+23, 2.4397e6)
- ... VENUS = (4.869e+24, 6.0518e6)
- ... EARTH = (5.976e+24, 6.37814e6)
- ... MARS = (6.421e+23, 3.3972e6)
- ... JUPITER = (1.9e+27, 7.1492e7)
- ... SATURN = (5.688e+26, 6.0268e7)
- ... URANUS = (8.686e+25, 2.5559e7)
- ... NEPTUNE = (1.024e+26, 2.4746e7)
- ... def __init__(self, mass, radius):
- ... self.mass = mass # in kilograms
- ... self.radius = radius # in meters
- ... @property
- ... def surface_gravity(self):
- ... # universal gravitational constant (m3 kg-1 s-2)
- ... G = 6.67300E-11
- ... return G * self.mass / (self.radius * self.radius)
- ...
- >>> Planet.EARTH.value
- (5.976e+24, 6378140.0)
- >>> Planet.EARTH.surface_gravity
- 9.802652743337129
-
-
-How are Enums different?
-------------------------
-
-Enums have a custom metaclass that affects many aspects of both derived Enum
-classes and their instances (members).
-
-
-Enum Classes
-^^^^^^^^^^^^
-
-The ``EnumMeta`` metaclass is responsible for providing the
-``__contains__``, ``__dir__``, ``__iter__`` and other methods that
-allow one to do things with an ``Enum`` class that fail on a typical
-class, such as ``list(Color)`` or ``some_var in Color``. ``EnumMeta`` is
-responsible for ensuring that various other methods on the final ``Enum``
-class are correct (such as ``__new__``, ``__getnewargs__``,
-``__str__`` and ``__repr__``)
-
-
-Enum Members (aka instances)
-^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-The most interesting thing about Enum members is that they are singletons.
-``EnumMeta`` creates them all while it is creating the ``Enum``
-class itself, and then puts a custom ``__new__`` in place to ensure
-that no new ones are ever instantiated by returning only the existing
-member instances.
-
-
-Finer Points
-^^^^^^^^^^^^
-
-Enum members are instances of an Enum class, and even though they are
-accessible as ``EnumClass.member``, they are not accessible directly from
-the member::
-
- >>> Color.red
- <Color.red: 1>
- >>> Color.red.blue
- Traceback (most recent call last):
- ...
- AttributeError: 'Color' object has no attribute 'blue'
-
-Likewise, ``__members__`` is only available on the class.
-
-In Python 3.x ``__members__`` is always an ``OrderedDict``, with the order being
-the definition order. In Python 2.7 ``__members__`` is an ``OrderedDict`` if
-``__order__`` was specified, and a plain ``dict`` otherwise. In all other Python
-2.x versions ``__members__`` is a plain ``dict`` even if ``__order__`` was specified
-as the ``OrderedDict`` type didn't exist yet.
-
-If you give your ``Enum`` subclass extra methods, like the `Planet`_
-class above, those methods will show up in a `dir` of the member,
-but not of the class::
-
- >>> dir(Planet)
- ['EARTH', 'JUPITER', 'MARS', 'MERCURY', 'NEPTUNE', 'SATURN', 'URANUS',
- 'VENUS', '__class__', '__doc__', '__members__', '__module__']
- >>> dir(Planet.EARTH)
- ['__class__', '__doc__', '__module__', 'name', 'surface_gravity', 'value']
-
-A ``__new__`` method will only be used for the creation of the
-``Enum`` members -- after that it is replaced. This means if you wish to
-change how ``Enum`` members are looked up you either have to write a
-helper function or a ``classmethod``.