Question

我一直在搞乱python的枚举库，并遇到了一个难题。在文档中，它们显示了auto-numbering enum的示例，其中定义了一些内容：

class Color(AutoNumber):
    red = ()
    green = ()
    ...

我想创建一个类似的类，但是该值会自动从成员的名称设置并保留从str和enum mixin stuff获得的功能

类似于：

class Animal(MagicStrEnum):
    horse = ()
    dog = ()

Animal.dog == 'dog' # True

我查看了枚举模块的源代码，并尝试了很多变体，其中包含__new__和EnumMeta类

Answer 1

更新：2017-03-01

在Python 3.6（和Aenum 2.0 ¹）中添加了Flag和IntFlag个类;其中一部分是一个新的auto() helper，这使得这很简单：

>>> class AutoName(Enum):
...     def _generate_next_value_(name, start, count, last_values):
...         return name
...
>>> class Ordinal(AutoName):
...     NORTH = auto()
...     SOUTH = auto()
...     EAST = auto()
...     WEST = auto()
...
>>> list(Ordinal)
[<Ordinal.NORTH: 'NORTH'>, <Ordinal.SOUTH: 'SOUTH'>, <Ordinal.EAST: 'EAST'>, <Ordinal.WEST: 'WEST'>]

原始回答

AutoStr类的难点在于枚举成员的名称未传递给创建它的代码，因此无法使用。另一个问题是str是不可变的，因此我们无法在创建后更改这些类型的枚举（例如，使用class decorator）。

最简单的方法是使用Functional API：

Animal = Enum('Animal', [(a, a) for a in ('horse', 'dog')], type=str)

给了我们：

>>> list(Animal)
[<Animal.horse: 'horse'>, <Animal.dog: 'dog'>]

>>> Animal.dog == 'dog'
True

下一个最简单的事情，假设你想为将来的枚举使用创建一个基类，就像我的DocEnem：

class DocEnum(Enum):
    """
    compares equal to all cased versions of its name
    accepts a doctring for each member
    """
    def __new__(cls, *args):
        """Ignores arguments (will be handled in __init__)"""
        obj = object.__new__(cls)
        obj._value_ = None
        return obj

    def __init__(self, doc=None):
        # first, fix _value_
        self._value_ = self._name_.lower()
        self.__doc__ = doc

    def __eq__(self, other):
        if isinstance(other, basestring):
            return self._value_ == other.lower()
        elif not isinstance(other, self.__class__):
            return NotImplemented
        return self is other

    def __ne__(self, other):
        return not self == other

并在使用中：

class SpecKind(DocEnum):
    REQUIRED = "required value"
    OPTION = "single value per name"
    MULTI = "multiple values per name (list form)"
    FLAG = "boolean value per name"
    KEYWORD = 'unknown options'

请注意，与第一个选项不同，DocEnum成员不 str。

如果你想这么做的话：子类EnumMeta并在创建成员之前摆弄新的Enum的类字典：

from enum import EnumMeta, Enum, _EnumDict class StrEnumMeta(EnumMeta): def __new__(metacls, cls, bases, oldclassdict): """ Scan through `oldclassdict` and convert any value that is a plain tuple into a `str` of the name instead """ newclassdict = _EnumDict() for k, v in oldclassdict.items(): if v == (): v = k newclassdict[k] = v return super().__new__(metacls, cls, bases, newclassdict) class AutoStrEnum(str, Enum, metaclass=StrEnumMeta): "base class for name=value str enums" class Animal(AutoStrEnum): horse = () dog = () whale = () print(Animal.horse) print(Animal.horse == 'horse') print(Animal.horse.name, Animal.horse.value)

这给了我们：

Animal.horse True horse horse

¹披露：我是Python stdlib Enum，enum34 backport和Advanced Enumeration (aenum)图书馆的作者。

Answer 2

也许您正在寻找由Enum类自动提供的name属性

>>> class Animal(Enum):
...     ant = 1
...     bee = 2
...     cat = 3
...     dog = 4
...

>>> Animal.ant.name == "ant"
True

虽然你真的想要在脚下射击自己。而且我相信这会引入一整套陷阱（我已经消除了最明显的问题）。

from enum import Enum, EnumMeta, _EnumDict

class AutoStrEnumDict(_EnumDict):
    def __setitem__(self, key, value):
        super().__setitem__(key, key)

class AutoStrEnumMeta(EnumMeta):
    @classmethod
    def __prepare__(metacls, cls, bases):
        return AutoStrEnumDict()
    def __init__(self, name, bases, attrs):
        super().__init__(name, bases, attrs)
        # override Enum.__str__
        # can't put these on the class directly otherwise EnumMeta overwrites them
        # should also consider resetting __repr__, __format__ and __reduce_ex__
        if self.__str__ is not str.__str__:
            self.__str__ = str.__str__

class AutoStrNameEnum(str, Enum, metaclass=AutoStrEnumMeta):
    pass

class Animal(AutoStrNameEnum):
    horse = ()
    dog = ()

print(Animal.horse)
assert Animal.horse == "horse"
assert str(Animal.horse) == "horse" 
# and not equal to "Animal.horse" (the gotcha mentioned earlier)

自动将枚举成员的值设置为其名称

2 个答案: