Python 2.7和find_name()

下面是所选思想的一个易于阅读的实现，其中包含一些辅助方法，这些方法可能比“reverse_mapping”更python化，使用起来更简洁。要求Python >= 2.7。

为了解决下面的一些注释，枚举对于防止代码中的拼写错误非常有用，例如对于状态机，错误分类器等。

def Enum(*sequential, **named):
  """Generate a new enum type. Usage example:

  ErrorClass = Enum('STOP','GO')
  print ErrorClass.find_name(ErrorClass.STOP)
    = "STOP"
  print ErrorClass.find_val("STOP")
    = 0
  ErrorClass.FOO     # Raises AttributeError
  """
  enums = { v:k for k,v in enumerate(sequential) } if not named else named

  @classmethod
  def find_name(cls, val):
    result = [ k for k,v in cls.__dict__.iteritems() if v == val ]
    if not len(result):
        raise ValueError("Value %s not found in Enum" % val)
    return result[0]

  @classmethod
  def find_val(cls, n):
    return getattr(cls, n)

  enums['find_val'] = find_val
  enums['find_name'] = find_name
  return type('Enum', (), enums)

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())

保持简单，使用旧的Python 2。x(参见下面的Python 3!):

class Enum(object): 
    def __init__(self, tupleList):
            self.tupleList = tupleList
    
    def __getattr__(self, name):
            return self.tupleList.index(name)

然后:

DIRECTION = Enum(('UP', 'DOWN', 'LEFT', 'RIGHT'))
DIRECTION.DOWN
1

在使用Python 3时保持简单:

from enum import Enum
class MyEnum(Enum):
    UP = 1
    DOWN = 2
    LEFT = 3
    RIGHT = 4

然后:

MyEnum.DOWN

参见:https://docs.python.org/3/library/enum.html

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)

这里是一个实现:

class Enum(set):
    def __getattr__(self, name):
        if name in self:
            return name
        raise AttributeError

下面是它的用法:

Animals = Enum(["DOG", "CAT", "HORSE"])

print(Animals.DOG)

下面是亚历克·托马斯解决方案的一个变种:

def enum(*args, **kwargs):
    return type('Enum', (), dict((y, x) for x, y in enumerate(args), **kwargs)) 

x = enum('POOH', 'TIGGER', 'EEYORE', 'ROO', 'PIGLET', 'RABBIT', 'OWL')
assert x.POOH == 0
assert x.TIGGER == 1