遵循Aaron Maenpaa提出的类Java枚举实现，我得出了以下结论。我们的想法是使它具有通用性和可解析性。

class Enum:
    #'''
    #Java like implementation for enums.
    #
    #Usage:
    #class Tool(Enum): name = 'Tool'
    #Tool.DRILL = Tool.register('drill')
    #Tool.HAMMER = Tool.register('hammer')
    #Tool.WRENCH = Tool.register('wrench')
    #'''

    name = 'Enum'    # Enum name
    _reg = dict([])   # Enum registered values

    @classmethod
    def register(cls, value):
        #'''
        #Registers a new value in this enum.
        #
        #@param value: New enum value.
        #
        #@return: New value wrapper instance.
        #'''
        inst = cls(value)
        cls._reg[value] = inst
        return inst

    @classmethod
    def parse(cls, value):
        #'''
        #Parses a value, returning the enum instance.
        #
        #@param value: Enum value.
        #
        #@return: Value corresp instance.        
        #'''
        return cls._reg.get(value)    

    def __init__(self, value):
        #'''
        #Constructor (only for internal use).
        #'''
        self.value = value

    def __str__(self):
        #'''
        #str() overload.
        #'''
        return self.value

    def __repr__(self):
        #'''
        #repr() overload.
        #'''
        return "<" + self.name + ": " + self.value + ">"

Python的标准是PEP 435，所以在Python 3.4+中可以使用Enum类:

>>> from enum import Enum
>>> class Colors(Enum):
...     red = 1
...     green = 2
...     blue = 3
>>> for color in Colors: print color
Colors.red
Colors.green
Colors.blue

如果你需要数值，这是最快的方法:

dog, cat, rabbit = range(3)

在Python 3中。X你也可以在最后添加一个星号占位符，它将吸收范围内所有剩余的值，以防你不介意浪费内存和无法计数:

dog, cat, rabbit, horse, *_ = range(100)

def M_add_class_attribs(attribs):
    def foo(name, bases, dict_):
        for v, k in attribs:
            dict_[k] = v
        return type(name, bases, dict_)
    return foo

def enum(*names):
    class Foo(object):
        __metaclass__ = M_add_class_attribs(enumerate(names))
        def __setattr__(self, name, value):  # this makes it read-only
            raise NotImplementedError
    return Foo()

像这样使用它:

Animal = enum('DOG', 'CAT')
Animal.DOG # returns 0
Animal.CAT # returns 1
Animal.DOG = 2 # raises NotImplementedError

如果你只想要唯一的符号，不关心值，替换这行:

__metaclass__ = M_add_class_attribs(enumerate(names))

用这个:

__metaclass__ = M_add_class_attribs((object(), name) for name in names)

另一个非常简单的Python枚举实现，使用namedtuple:

from collections import namedtuple

def enum(*keys):
    return namedtuple('Enum', keys)(*keys)

MyEnum = enum('FOO', 'BAR', 'BAZ')

,或者

# With sequential number values
def enum(*keys):
    return namedtuple('Enum', keys)(*range(len(keys)))

# From a dict / keyword args
def enum(**kwargs):
    return namedtuple('Enum', kwargs.keys())(*kwargs.values())




# Example for dictionary param:
values = {"Salad": 20, "Carrot": 99, "Tomato": "No i'm not"} 
Vegetables= enum(**values)

# >>> print(Vegetables.Tomato)        'No i'm not'


# Example for keyworded params: 
Fruits = enum(Apple="Steve Jobs", Peach=1, Banana=2)

# >>> print(Fruits.Apple)             'Steve Jobs'

就像上面子类设置的方法一样，这允许:

'FOO' in MyEnum
other = MyEnum.FOO
assert other == MyEnum.FOO

但是具有更大的灵活性，因为它可以有不同的键和值。这允许

MyEnum.FOO < MyEnum.BAR

如果使用填充连续数字值的版本，则按预期操作。

为什么枚举必须是整数?不幸的是，在不改变Python语言的情况下，我想不出任何好看的构造来生成它，所以我将使用字符串:

class Enumerator(object):
    def __init__(self, name):
        self.name = name

    def __eq__(self, other):
        if self.name == other:
            return True
        return self is other

    def __ne__(self, other):
        if self.name != other:
            return False
        return self is other

    def __repr__(self):
        return 'Enumerator({0})'.format(self.name)

    def __str__(self):
        return self.name

class Enum(object):
    def __init__(self, *enumerators):
        for e in enumerators:
            setattr(self, e, Enumerator(e))
    def __getitem__(self, key):
        return getattr(self, key)

也许现在更好的是，为了配置文件或其他远程输入，我们可以自然地对字符串进行测试。

例子:

class Cow(object):
    State = Enum(
        'standing',
        'walking',
        'eating',
        'mooing',
        'sleeping',
        'dead',
        'dying'
    )
    state = State.standing

In [1]: from enum import Enum

In [2]: c = Cow()

In [3]: c2 = Cow()

In [4]: c.state, c2.state
Out[4]: (Enumerator(standing), Enumerator(standing))

In [5]: c.state == c2.state
Out[5]: True

In [6]: c.State.mooing
Out[6]: Enumerator(mooing)

In [7]: c.State['mooing']
Out[7]: Enumerator(mooing)

In [8]: c.state = Cow.State.dead

In [9]: c.state == c2.state
Out[9]: False

In [10]: c.state == Cow.State.dead
Out[10]: True

In [11]: c.state == 'dead'
Out[11]: True

In [12]: c.state == Cow.State['dead']
Out[11]: True