Closes issue 17947. Adds PEP-0435 (Adding an Enum type to the Python standard library).
Missing files added.
News entry added.
diff --git a/Lib/enum.py b/Lib/enum.py
new file mode 100644
index 0000000..775489b
--- /dev/null
+++ b/Lib/enum.py
@@ -0,0 +1,465 @@
+"""Python Enumerations"""
+
+import sys
+from collections import OrderedDict
+from types import MappingProxyType
+
+__all__ = ['Enum', 'IntEnum']
+
+
+class _RouteClassAttributeToGetattr:
+ """Route attribute access on a class to __getattr__.
+
+ This is a descriptor, used to define attributes that act differently when
+ accessed through an instance and through a class. Instance access remains
+ normal, but access to an attribute through a class will be routed to the
+ class's __getattr__ method; this is done by raising AttributeError.
+
+ """
+ def __init__(self, fget=None):
+ self.fget = fget
+
+ def __get__(self, instance, ownerclass=None):
+ if instance is None:
+ raise AttributeError()
+ return self.fget(instance)
+
+ def __set__(self, instance, value):
+ raise AttributeError("can't set attribute")
+
+ def __delete__(self, instance):
+ raise AttributeError("can't delete attribute")
+
+
+def _is_dunder(name):
+ """Returns True if a __dunder__ name, False otherwise."""
+ return (name[:2] == name[-2:] == '__' and
+ name[2:3] != '_' and
+ name[-3:-2] != '_')
+
+
+def _is_sunder(name):
+ """Returns True if a _sunder_ name, False otherwise."""
+ return (name[0] == name[-1] == '_' and
+ name[1:2] != '_' and
+ name[-2:-1] != '_')
+
+
+def _make_class_unpicklable(cls):
+ """Make the given class un-picklable."""
+ def _break_on_call_reduce(self):
+ raise TypeError('%r cannot be pickled' % self)
+ cls.__reduce__ = _break_on_call_reduce
+ cls.__module__ = '<unknown>'
+
+
+class _EnumDict(dict):
+ """Keeps track of definition order of the enum items.
+
+ EnumMeta will use the names found in self._member_names as the
+ enumeration member names.
+
+ """
+ def __init__(self):
+ super().__init__()
+ self._member_names = []
+
+ def __setitem__(self, key, value):
+ """Changes anything not dundered or that doesn't have __get__.
+
+ If a descriptor is added with the same name as an enum member, the name
+ is removed from _member_names (this may leave a hole in the numerical
+ sequence of values).
+
+ If an enum member name is used twice, an error is raised; duplicate
+ values are not checked for.
+
+ Single underscore (sunder) names are reserved.
+
+ """
+ if _is_sunder(key):
+ raise ValueError('_names_ are reserved for future Enum use')
+ elif _is_dunder(key) or hasattr(value, '__get__'):
+ if key in self._member_names:
+ # overwriting an enum with a method? then remove the name from
+ # _member_names or it will become an enum anyway when the class
+ # is created
+ self._member_names.remove(key)
+ else:
+ if key in self._member_names:
+ raise TypeError('Attempted to reuse key: %r' % key)
+ self._member_names.append(key)
+ super().__setitem__(key, value)
+
+
+# Dummy value for Enum as EnumMeta explicity checks for it, but of course until
+# EnumMeta finishes running the first time the Enum class doesn't exist. This
+# is also why there are checks in EnumMeta like `if Enum is not None`
+Enum = None
+
+
+class EnumMeta(type):
+ """Metaclass for Enum"""
+ @classmethod
+ def __prepare__(metacls, cls, bases):
+ return _EnumDict()
+
+ def __new__(metacls, cls, bases, classdict):
+ # an Enum class is final once enumeration items have been defined; it
+ # cannot be mixed with other types (int, float, etc.) if it has an
+ # inherited __new__ unless a new __new__ is defined (or the resulting
+ # class will fail).
+ member_type, first_enum = metacls._get_mixins_(bases)
+ __new__, save_new, use_args = metacls._find_new_(classdict, member_type,
+ first_enum)
+
+ # save enum items into separate mapping so they don't get baked into
+ # the new class
+ members = {k: classdict[k] for k in classdict._member_names}
+ for name in classdict._member_names:
+ del classdict[name]
+
+ # check for illegal enum names (any others?)
+ invalid_names = set(members) & {'mro', }
+ if invalid_names:
+ raise ValueError('Invalid enum member name: {0}'.format(
+ ','.join(invalid_names)))
+
+ # create our new Enum type
+ enum_class = super().__new__(metacls, cls, bases, classdict)
+ enum_class._member_names = [] # names in definition order
+ enum_class._member_map = OrderedDict() # name->value map
+
+ # Reverse value->name map for hashable values.
+ enum_class._value2member_map = {}
+
+ # check for a __getnewargs__, and if not present sabotage
+ # pickling, since it won't work anyway
+ if (member_type is not object and
+ member_type.__dict__.get('__getnewargs__') is None
+ ):
+ _make_class_unpicklable(enum_class)
+
+ # instantiate them, checking for duplicates as we go
+ # we instantiate first instead of checking for duplicates first in case
+ # a custom __new__ is doing something funky with the values -- such as
+ # auto-numbering ;)
+ for member_name in classdict._member_names:
+ value = members[member_name]
+ if not isinstance(value, tuple):
+ args = (value, )
+ else:
+ args = value
+ if member_type is tuple: # special case for tuple enums
+ args = (args, ) # wrap it one more time
+ if not use_args:
+ enum_member = __new__(enum_class)
+ enum_member._value = value
+ else:
+ enum_member = __new__(enum_class, *args)
+ if not hasattr(enum_member, '_value'):
+ enum_member._value = member_type(*args)
+ enum_member._member_type = member_type
+ enum_member._name = member_name
+ enum_member.__init__(*args)
+ # If another member with the same value was already defined, the
+ # new member becomes an alias to the existing one.
+ for name, canonical_member in enum_class._member_map.items():
+ if canonical_member.value == enum_member._value:
+ enum_member = canonical_member
+ break
+ else:
+ # Aliases don't appear in member names (only in __members__).
+ enum_class._member_names.append(member_name)
+ enum_class._member_map[member_name] = enum_member
+ try:
+ # This may fail if value is not hashable. We can't add the value
+ # to the map, and by-value lookups for this value will be
+ # linear.
+ enum_class._value2member_map[value] = enum_member
+ except TypeError:
+ pass
+
+ # double check that repr and friends are not the mixin's or various
+ # things break (such as pickle)
+ for name in ('__repr__', '__str__', '__getnewargs__'):
+ class_method = getattr(enum_class, name)
+ obj_method = getattr(member_type, name, None)
+ enum_method = getattr(first_enum, name, None)
+ if obj_method is not None and obj_method is class_method:
+ setattr(enum_class, name, enum_method)
+
+ # replace any other __new__ with our own (as long as Enum is not None,
+ # anyway) -- again, this is to support pickle
+ if Enum is not None:
+ # if the user defined their own __new__, save it before it gets
+ # clobbered in case they subclass later
+ if save_new:
+ enum_class.__new_member__ = __new__
+ enum_class.__new__ = Enum.__new__
+ return enum_class
+
+ def __call__(cls, value, names=None, *, module=None, type=None):
+ """Either returns an existing member, or creates a new enum class.
+
+ This method is used both when an enum class is given a value to match
+ to an enumeration member (i.e. Color(3)) and for the functional API
+ (i.e. Color = Enum('Color', names='red green blue')).
+
+ When used for the functional API: `module`, if set, will be stored in
+ the new class' __module__ attribute; `type`, if set, will be mixed in
+ as the first base class.
+
+ Note: if `module` is not set this routine will attempt to discover the
+ calling module by walking the frame stack; if this is unsuccessful
+ the resulting class will not be pickleable.
+
+ """
+ if names is None: # simple value lookup
+ return cls.__new__(cls, value)
+ # otherwise, functional API: we're creating a new Enum type
+ return cls._create_(value, names, module=module, type=type)
+
+ def __contains__(cls, member):
+ return isinstance(member, cls) and member.name in cls._member_map
+
+ def __dir__(self):
+ return ['__class__', '__doc__', '__members__'] + self._member_names
+
+ @property
+ def __members__(cls):
+ """Returns a mapping of member name->value.
+
+ This mapping lists all enum members, including aliases. Note that this
+ is a read-only view of the internal mapping.
+
+ """
+ return MappingProxyType(cls._member_map)
+
+ def __getattr__(cls, name):
+ """Return the enum member matching `name`
+
+ We use __getattr__ instead of descriptors or inserting into the enum
+ class' __dict__ in order to support `name` and `value` being both
+ properties for enum members (which live in the class' __dict__) and
+ enum members themselves.
+
+ """
+ if _is_dunder(name):
+ raise AttributeError(name)
+ try:
+ return cls._member_map[name]
+ except KeyError:
+ raise AttributeError(name) from None
+
+ def __getitem__(cls, name):
+ return cls._member_map[name]
+
+ def __iter__(cls):
+ return (cls._member_map[name] for name in cls._member_names)
+
+ def __len__(cls):
+ return len(cls._member_names)
+
+ def __repr__(cls):
+ return "<enum %r>" % cls.__name__
+
+ def _create_(cls, class_name, names=None, *, module=None, type=None):
+ """Convenience method to create a new Enum class.
+
+ `names` can be:
+
+ * A string containing member names, separated either with spaces or
+ commas. Values are auto-numbered from 1.
+ * An iterable of member names. Values are auto-numbered from 1.
+ * An iterable of (member name, value) pairs.
+ * A mapping of member name -> value.
+
+ """
+ metacls = cls.__class__
+ bases = (cls, ) if type is None else (type, cls)
+ classdict = metacls.__prepare__(class_name, bases)
+
+ # special processing needed for names?
+ if isinstance(names, str):
+ names = names.replace(',', ' ').split()
+ if isinstance(names, (tuple, list)) and isinstance(names[0], str):
+ names = [(e, i) for (i, e) in enumerate(names, 1)]
+
+ # Here, names is either an iterable of (name, value) or a mapping.
+ for item in names:
+ if isinstance(item, str):
+ member_name, member_value = item, names[item]
+ else:
+ member_name, member_value = item
+ classdict[member_name] = member_value
+ enum_class = metacls.__new__(metacls, class_name, bases, classdict)
+
+ # TODO: replace the frame hack if a blessed way to know the calling
+ # module is ever developed
+ if module is None:
+ try:
+ module = sys._getframe(2).f_globals['__name__']
+ except (AttributeError, ValueError) as exc:
+ pass
+ if module is None:
+ _make_class_unpicklable(enum_class)
+ else:
+ enum_class.__module__ = module
+
+ return enum_class
+
+ @staticmethod
+ def _get_mixins_(bases):
+ """Returns the type for creating enum members, and the first inherited
+ enum class.
+
+ bases: the tuple of bases that was given to __new__
+
+ """
+ if not bases:
+ return object, Enum
+
+ # double check that we are not subclassing a class with existing
+ # enumeration members; while we're at it, see if any other data
+ # type has been mixed in so we can use the correct __new__
+ member_type = first_enum = None
+ for base in bases:
+ if (base is not Enum and
+ issubclass(base, Enum) and
+ base._member_names):
+ raise TypeError("Cannot extend enumerations")
+ # base is now the last base in bases
+ if not issubclass(base, Enum):
+ raise TypeError("new enumerations must be created as "
+ "`ClassName([mixin_type,] enum_type)`")
+
+ # get correct mix-in type (either mix-in type of Enum subclass, or
+ # first base if last base is Enum)
+ if not issubclass(bases[0], Enum):
+ member_type = bases[0] # first data type
+ first_enum = bases[-1] # enum type
+ else:
+ for base in bases[0].__mro__:
+ # most common: (IntEnum, int, Enum, object)
+ # possible: (<Enum 'AutoIntEnum'>, <Enum 'IntEnum'>,
+ # <class 'int'>, <Enum 'Enum'>,
+ # <class 'object'>)
+ if issubclass(base, Enum):
+ if first_enum is None:
+ first_enum = base
+ else:
+ if member_type is None:
+ member_type = base
+
+ return member_type, first_enum
+
+ @staticmethod
+ def _find_new_(classdict, member_type, first_enum):
+ """Returns the __new__ to be used for creating the enum members.
+
+ classdict: the class dictionary given to __new__
+ member_type: the data type whose __new__ will be used by default
+ first_enum: enumeration to check for an overriding __new__
+
+ """
+ # now find the correct __new__, checking to see of one was defined
+ # by the user; also check earlier enum classes in case a __new__ was
+ # saved as __new_member__
+ __new__ = classdict.get('__new__', None)
+
+ # should __new__ be saved as __new_member__ later?
+ save_new = __new__ is not None
+
+ if __new__ is None:
+ # check all possibles for __new_member__ before falling back to
+ # __new__
+ for method in ('__new_member__', '__new__'):
+ for possible in (member_type, first_enum):
+ target = getattr(possible, method, None)
+ if target not in {
+ None,
+ None.__new__,
+ object.__new__,
+ Enum.__new__,
+ }:
+ __new__ = target
+ break
+ if __new__ is not None:
+ break
+ else:
+ __new__ = object.__new__
+
+ # if a non-object.__new__ is used then whatever value/tuple was
+ # assigned to the enum member name will be passed to __new__ and to the
+ # new enum member's __init__
+ if __new__ is object.__new__:
+ use_args = False
+ else:
+ use_args = True
+
+ return __new__, save_new, use_args
+
+
+class Enum(metaclass=EnumMeta):
+ """Generic enumeration.
+
+ Derive from this class to define new enumerations.
+
+ """
+ def __new__(cls, value):
+ # all enum instances are actually created during class construction
+ # without calling this method; this method is called by the metaclass'
+ # __call__ (i.e. Color(3) ), and by pickle
+ if type(value) is cls:
+ # For lookups like Color(Color.red)
+ return value
+ # by-value search for a matching enum member
+ # see if it's in the reverse mapping (for hashable values)
+ if value in cls._value2member_map:
+ return cls._value2member_map[value]
+ # not there, now do long search -- O(n) behavior
+ for member in cls._member_map.values():
+ if member.value == value:
+ return member
+ raise ValueError("%s is not a valid %s" % (value, cls.__name__))
+
+ def __repr__(self):
+ return "<%s.%s: %r>" % (
+ self.__class__.__name__, self._name, self._value)
+
+ def __str__(self):
+ return "%s.%s" % (self.__class__.__name__, self._name)
+
+ def __dir__(self):
+ return (['__class__', '__doc__', 'name', 'value'])
+
+ def __eq__(self, other):
+ if type(other) is self.__class__:
+ return self is other
+ return NotImplemented
+
+ def __getnewargs__(self):
+ return (self._value, )
+
+ def __hash__(self):
+ return hash(self._name)
+
+ # _RouteClassAttributeToGetattr is used to provide access to the `name`
+ # and `value` properties of enum members while keeping some measure of
+ # protection from modification, while still allowing for an enumeration
+ # to have members named `name` and `value`. This works because enumeration
+ # members are not set directly on the enum class -- __getattr__ is
+ # used to look them up.
+
+ @_RouteClassAttributeToGetattr
+ def name(self):
+ return self._name
+
+ @_RouteClassAttributeToGetattr
+ def value(self):
+ return self._value
+
+
+class IntEnum(int, Enum):
+ """Enum where members are also (and must be) ints"""