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())

从Python 3.4开始，正式支持枚举。您可以在Python 3.4文档页面上找到文档和示例。

枚举是使用类语法创建的，这使得它们很容易 读和写。中描述了另一种创建方法 功能的API。定义枚举，子类Enum如下所示:

from enum import Enum
class Color(Enum):
     red = 1
     green = 2
     blue = 3

以下是我认为有价值的方法:

允许>和<基于枚举中的顺序进行比较，而不是词法顺序 可以地址项目的名称，属性或索引:x.a, x['a']或x[0] 支持[:]或[-1]等切片操作

最重要的是防止不同类型的枚举之间的比较!

基于http://code.activestate.com/recipes/413486-first-class-enums-in-python。

这里包含了许多文档测试，以说明这种方法的不同之处。

def enum(*names):
    """
SYNOPSIS
    Well-behaved enumerated type, easier than creating custom classes

DESCRIPTION
    Create a custom type that implements an enumeration.  Similar in concept
    to a C enum but with some additional capabilities and protections.  See
    http://code.activestate.com/recipes/413486-first-class-enums-in-python/.

PARAMETERS
    names       Ordered list of names.  The order in which names are given
                will be the sort order in the enum type.  Duplicate names
                are not allowed.  Unicode names are mapped to ASCII.

RETURNS
    Object of type enum, with the input names and the enumerated values.

EXAMPLES
    >>> letters = enum('a','e','i','o','u','b','c','y','z')
    >>> letters.a < letters.e
    True

    ## index by property
    >>> letters.a
    a

    ## index by position
    >>> letters[0]
    a

    ## index by name, helpful for bridging string inputs to enum
    >>> letters['a']
    a

    ## sorting by order in the enum() create, not character value
    >>> letters.u < letters.b
    True

    ## normal slicing operations available
    >>> letters[-1]
    z

    ## error since there are not 100 items in enum
    >>> letters[99]
    Traceback (most recent call last):
        ...
    IndexError: tuple index out of range

    ## error since name does not exist in enum
    >>> letters['ggg']
    Traceback (most recent call last):
        ...
    ValueError: tuple.index(x): x not in tuple

    ## enums must be named using valid Python identifiers
    >>> numbers = enum(1,2,3,4)
    Traceback (most recent call last):
        ...
    AssertionError: Enum values must be string or unicode

    >>> a = enum('-a','-b')
    Traceback (most recent call last):
        ...
    TypeError: Error when calling the metaclass bases
        __slots__ must be identifiers

    ## create another enum
    >>> tags = enum('a','b','c')
    >>> tags.a
    a
    >>> letters.a
    a

    ## can't compare values from different enums
    >>> letters.a == tags.a
    Traceback (most recent call last):
        ...
    AssertionError: Only values from the same enum are comparable

    >>> letters.a < tags.a
    Traceback (most recent call last):
        ...
    AssertionError: Only values from the same enum are comparable

    ## can't update enum after create
    >>> letters.a = 'x'
    Traceback (most recent call last):
        ...
    AttributeError: 'EnumClass' object attribute 'a' is read-only

    ## can't update enum after create
    >>> del letters.u
    Traceback (most recent call last):
        ...
    AttributeError: 'EnumClass' object attribute 'u' is read-only

    ## can't have non-unique enum values
    >>> x = enum('a','b','c','a')
    Traceback (most recent call last):
        ...
    AssertionError: Enums must not repeat values

    ## can't have zero enum values
    >>> x = enum()
    Traceback (most recent call last):
        ...
    AssertionError: Empty enums are not supported

    ## can't have enum values that look like special function names
    ## since these could collide and lead to non-obvious errors
    >>> x = enum('a','b','c','__cmp__')
    Traceback (most recent call last):
        ...
    AssertionError: Enum values beginning with __ are not supported

LIMITATIONS
    Enum values of unicode type are not preserved, mapped to ASCII instead.

    """
    ## must have at least one enum value
    assert names, 'Empty enums are not supported'
    ## enum values must be strings
    assert len([i for i in names if not isinstance(i, types.StringTypes) and not \
        isinstance(i, unicode)]) == 0, 'Enum values must be string or unicode'
    ## enum values must not collide with special function names
    assert len([i for i in names if i.startswith("__")]) == 0,\
        'Enum values beginning with __ are not supported'
    ## each enum value must be unique from all others
    assert names == uniquify(names), 'Enums must not repeat values'

    class EnumClass(object):
        """ See parent function for explanation """

        __slots__ = names

        def __iter__(self):
            return iter(constants)

        def __len__(self):
            return len(constants)

        def __getitem__(self, i):
            ## this makes xx['name'] possible
            if isinstance(i, types.StringTypes):
                i = names.index(i)
            ## handles the more normal xx[0]
            return constants[i]

        def __repr__(self):
            return 'enum' + str(names)

        def __str__(self):
            return 'enum ' + str(constants)

        def index(self, i):
            return names.index(i)

    class EnumValue(object):
        """ See parent function for explanation """

        __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):
            assert self.enumtype is other.enumtype, 'Only values from the same enum are comparable'
            return cmp(self.value, other.value)

        def __invert__(self):
            return constants[maximum - self.value]

        def __nonzero__(self):
            ## return bool(self.value)
            ## Original code led to bool(x[0])==False, not correct
            return True

        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

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

使用下面的方法。

TYPE = {'EAN13':   u'EAN-13',
        'CODE39':  u'Code 39',
        'CODE128': u'Code 128',
        'i25':     u'Interleaved 2 of 5',}

>>> TYPE.items()
[('EAN13', u'EAN-13'), ('i25', u'Interleaved 2 of 5'), ('CODE39', u'Code 39'), ('CODE128', u'Code 128')]
>>> TYPE.keys()
['EAN13', 'i25', 'CODE39', 'CODE128']
>>> TYPE.values()
[u'EAN-13', u'Interleaved 2 of 5', u'Code 39', u'Code 128']

我用它来选择Django模型，它看起来非常python化。它不是一个真正的Enum，但它完成了这项工作。

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