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 + ">"

Alexandru对枚举使用类常量的建议效果很好。

我还喜欢为每组常量添加字典，以查找人类可读的字符串表示。

这有两个目的:a)它提供了一种简单的方法来漂亮地打印你的枚举;b)字典在逻辑上对常量进行分组，以便您可以测试成员关系。

class Animal:    
  TYPE_DOG = 1
  TYPE_CAT = 2

  type2str = {
    TYPE_DOG: "dog",
    TYPE_CAT: "cat"
  }

  def __init__(self, type_):
    assert type_ in self.type2str.keys()
    self._type = type_

  def __repr__(self):
    return "<%s type=%s>" % (
        self.__class__.__name__, self.type2str[self._type].upper())

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 + ">"

这是我见过的最好的一个:“Python中的First Class Enums”

http://code.activestate.com/recipes/413486/

It gives you a class, and the class contains all the enums. The enums can be compared to each other, but don't have any particular value; you can't use them as an integer value. (I resisted this at first because I am used to C enums, which are integer values. But if you can't use it as an integer, you can't use it as an integer by mistake so overall I think it is a win.) Each enum is a unique value. You can print enums, you can iterate over them, you can test that an enum value is "in" the enum. It's pretty complete and slick.

编辑(cfi):上面的链接不兼容Python 3。下面是我将枚举.py移植到Python 3的端口:

def cmp(a,b):
   if a < b: return -1
   if b < a: return 1
   return 0


def Enum(*names):
   ##assert names, "Empty enums are not supported" # <- Don't like empty enums? Uncomment!

   class EnumClass(object):
      __slots__ = names
      def __iter__(self):        return iter(constants)
      def __len__(self):         return len(constants)
      def __getitem__(self, i):  return constants[i]
      def __repr__(self):        return 'Enum' + str(names)
      def __str__(self):         return 'enum ' + str(constants)

   class EnumValue(object):
      __slots__ = ('__value')
      def __init__(self, value): self.__value = value
      Value = property(lambda self: self.__value)
      EnumType = property(lambda self: EnumType)
      def __hash__(self):        return hash(self.__value)
      def __cmp__(self, other):
         # C fans might want to remove the following assertion
         # to make all enums comparable by ordinal value {;))
         assert self.EnumType is other.EnumType, "Only values from the same enum are comparable"
         return cmp(self.__value, other.__value)
      def __lt__(self, other):   return self.__cmp__(other) < 0
      def __eq__(self, other):   return self.__cmp__(other) == 0
      def __invert__(self):      return constants[maximum - self.__value]
      def __nonzero__(self):     return bool(self.__value)
      def __repr__(self):        return str(names[self.__value])

   maximum = len(names) - 1
   constants = [None] * len(names)
   for i, each in enumerate(names):
      val = EnumValue(i)
      setattr(EnumClass, each, val)
      constants[i] = val
   constants = tuple(constants)
   EnumType = EnumClass()
   return EnumType


if __name__ == '__main__':
   print( '\n*** Enum Demo ***')
   print( '--- Days of week ---')
   Days = Enum('Mo', 'Tu', 'We', 'Th', 'Fr', 'Sa', 'Su')
   print( Days)
   print( Days.Mo)
   print( Days.Fr)
   print( Days.Mo < Days.Fr)
   print( list(Days))
   for each in Days:
      print( 'Day:', each)
   print( '--- Yes/No ---')
   Confirmation = Enum('No', 'Yes')
   answer = Confirmation.No
   print( 'Your answer is not', ~answer)

在答案列表中没有看到这个，这是我想出的一个。它允许使用'in'关键字和len()方法:

class EnumTypeError(TypeError):
    pass

class Enum(object):
    """
    Minics enum type from different languages
    Usage:
    Letters = Enum(list('abc'))
    a = Letters.a
    print(a in Letters) # True
    print(54 in Letters) # False
    """
    def __init__(self, enums):
        if isinstance(enums, dict):
            self.__dict__.update(enums)
        elif isinstance(enums, list) or isinstance(enums, tuple):
            self.__dict__.update(**dict((v,k) for k,v in enumerate(enums)))
        else:
            raise EnumTypeError

    def __contains__(self, key):
        return key in self.__dict__.values()

    def __len__(self):
        return len(self.__dict__.values())


if __name__ == '__main__':
    print('Using a dictionary to create Enum:')
    Letters = Enum(dict((v,k) for k,v in enumerate(list('abcde'))))
    a = Letters.a
    print('\tIs a in e?', a in Letters)
    print('\tIs 54 in e?', 54 in Letters)
    print('\tLength of Letters enum:', len(Letters))

    print('\nUsing a list to create Enum:')
    Letters = Enum(list('abcde'))
    a = Letters.a
    print('\tIs a in e?', a in Letters)
    print('\tIs 54 in e?', 54 in Letters)
    print('\tLength of Letters enum:', len(Letters))

    try:
        # make sure we raise an exception if we pass an invalid arg
        Failure = Enum('This is a Failure')
        print('Failure')
    except EnumTypeError:
        print('Success!')

输出:

Using a dictionary to create Enum:
        Is a in e? True
        Is 54 in e? False
        Length of Letters enum: 5

Using a list to create Enum:
        Is a in e? True
        Is 54 in e? False
        Length of Letters enum: 5
Success!

在PEP 435之前，Python没有等效的，但你可以实现自己的。

就我个人而言，我喜欢保持简单(我在网上看到过一些非常复杂的例子)，就像这样……

class Animal:
    DOG = 1
    CAT = 2

x = Animal.DOG

在Python 3.4 (PEP 435)中，可以将Enum作为基类。这为您提供了一些额外的功能，详见PEP。例如，enum成员不同于整数，它们由名称和值组成。

from enum import Enum

class Animal(Enum):
    DOG = 1
    CAT = 2

print(Animal.DOG)
# <Animal.DOG: 1>

print(Animal.DOG.value)
# 1

print(Animal.DOG.name)
# "DOG"

如果您不想键入值，请使用以下快捷方式:

class Animal(Enum):
    DOG, CAT = range(2)

枚举实现可以转换为列表，并且是可迭代的。其成员的顺序是声明顺序，与它们的值无关。例如:

class Animal(Enum):
    DOG = 1
    CAT = 2
    COW = 0

list(Animal)
# [<Animal.DOG: 1>, <Animal.CAT: 2>, <Animal.COW: 0>]

[animal.value for animal in Animal]
# [1, 2, 0]

Animal.CAT in Animal
# True