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import sysfrom collections import OrderedDictfrom types import MappingProxyType, DynamicClassAttribute
__all__ = ['Enum', 'IntEnum', 'unique']
def _is_descriptor(obj): """Returns True if obj is a descriptor, False otherwise.""" return ( hasattr(obj, '__get__') or hasattr(obj, '__set__') or hasattr(obj, '__delete__'))
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] != '_' and len(name) > 4)
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] != '_' and len(name) > 2)
def _make_class_unpicklable(cls): """Make the given class un-picklable.""" def _break_on_call_reduce(self, proto): raise TypeError('%r cannot be pickled' % self) cls.__reduce_ex__ = _break_on_call_reduce cls.__module__ = '<unknown>'
class _EnumDict(dict): """Track enum member order and ensure member names are not reused.
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 not a descriptor.
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): pass elif key in self._member_names: # descriptor overwriting an enum? raise TypeError('Attempted to reuse key: %r' % key) elif not _is_descriptor(value): if key in self: # enum overwriting a descriptor? raise TypeError('Key already defined as: %r' % self[key]) self._member_names.append(key) super().__setitem__(key, value)
# Dummy value for Enum as EnumMeta explicitly 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 enum_class._member_type_ = member_type
# Reverse value->name map for hashable values. enum_class._value2member_map_ = {}
# If a custom type is mixed into the Enum, and it does not know how # to pickle itself, pickle.dumps will succeed but pickle.loads will # fail. Rather than have the error show up later and possibly far # from the source, sabotage the pickle protocol for this class so # that pickle.dumps also fails. # # However, if the new class implements its own __reduce_ex__, do not # sabotage -- it's on them to make sure it works correctly. We use # __reduce_ex__ instead of any of the others as it is preferred by # pickle over __reduce__, and it handles all pickle protocols. if '__reduce_ex__' not in classdict: if member_type is not object: methods = ('__getnewargs_ex__', '__getnewargs__', '__reduce_ex__', '__reduce__') if not any(m in member_type.__dict__ for m in methods): _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) if not hasattr(enum_member, '_value_'): enum_member._value_ = value else: enum_member = __new__(enum_class, *args) if not hasattr(enum_member, '_value_'): enum_member._value_ = member_type(*args) value = enum_member._value_ enum_member._name_ = member_name enum_member.__objclass__ = enum_class 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__', '__format__', '__reduce_ex__'): 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, qualname=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:
`value` will be the name of the new class.
`names` should be either a string of white-space/comma delimited names (values will start at 1), or an iterator/mapping of name, value pairs.
`module` should be set to the module this class is being created in; if it is not set, an attempt to find that module will be made, but if it fails the class will not be picklable.
`qualname` should be set to the actual location this class can be found at in its module; by default it is set to the global scope. If this is not correct, unpickling will fail in some circumstances.
`type`, if set, will be mixed in as the first base class.
"""
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, qualname=qualname, type=type)
def __contains__(cls, member): return isinstance(member, cls) and member._name_ in cls._member_map_
def __delattr__(cls, attr): # nicer error message when someone tries to delete an attribute # (see issue19025). if attr in cls._member_map_: raise AttributeError( "%s: cannot delete Enum member." % cls.__name__) super().__delattr__(attr)
def __dir__(self): return (['__class__', '__doc__', '__members__', '__module__'] + self._member_names_)
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_)
@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 __repr__(cls): return "<enum %r>" % cls.__name__
def __reversed__(cls): return (cls._member_map_[name] for name in reversed(cls._member_names_))
def __setattr__(cls, name, value): """Block attempts to reassign Enum members.
A simple assignment to the class namespace only changes one of the several possible ways to get an Enum member from the Enum class, resulting in an inconsistent Enumeration.
"""
member_map = cls.__dict__.get('_member_map_', {}) if name in member_map: raise AttributeError('Cannot reassign members.') super().__setattr__(name, value)
def _create_(cls, class_name, names=None, *, module=None, qualname=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 if qualname is not None: enum_class.__qualname__ = qualname
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) try: if value in cls._value2member_map_: return cls._value2member_map_[value] except TypeError: # not there, now do long search -- O(n) behavior for member in cls._member_map_.values(): if member._value_ == value: return member raise ValueError("%r 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): added_behavior = [ m for cls in self.__class__.mro() for m in cls.__dict__ if m[0] != '_' ] return (['__class__', '__doc__', '__module__', 'name', 'value'] + added_behavior)
def __format__(self, format_spec): # mixed-in Enums should use the mixed-in type's __format__, otherwise # we can get strange results with the Enum name showing up instead of # the value
# pure Enum branch if self._member_type_ is object: cls = str val = str(self) # mix-in branch else: cls = self._member_type_ val = self._value_ return cls.__format__(val, format_spec)
def __hash__(self): return hash(self._name_)
def __reduce_ex__(self, proto): return self.__class__, (self._value_, )
# DynamicClassAttribute 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.
@DynamicClassAttribute def name(self): """The name of the Enum member.""" return self._name_
@DynamicClassAttribute def value(self): """The value of the Enum member.""" return self._value_
class IntEnum(int, Enum): """Enum where members are also (and must be) ints"""
def unique(enumeration): """Class decorator for enumerations ensuring unique member values.""" duplicates = [] for name, member in enumeration.__members__.items(): if name != member.name: duplicates.append((name, member.name)) if duplicates: alias_details = ', '.join( ["%s -> %s" % (alias, name) for (alias, name) in duplicates]) raise ValueError('duplicate values found in %r: %s' % (enumeration, alias_details)) return enumeration
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