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Python: Enum枚举的实现

 dinghj 2014-04-17

      从C系语言过来用Python,好不容易适应了写代码不打花括号,突然有一天发现它居然木有枚举……于是stackoverflow了一把,发现神人的枚举(enum)实现到处都是,于是汉化总结过来。

如果是新版Python用户(Python 3.4 with PEP 435):

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from enum import Enum
Animal = Enum('Animal', 'ant bee cat dog')

 

or

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class Animals(Enum):
    ant = 1
    bee = 2
    cat = 3
    dog = 4

 

旧版Python用户可以充分发挥动态语言的优越性来构造枚举,有简单的:

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def enum(**enums):
    return type('Enum', (), enums)
Numbers = enum(ONE=1, TWO=2, THREE='three')
# Numbers.ONE == 1, Numbers.TWO == 2 and Numbers.THREE == 'three'

 

有复杂的:

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def enum(*sequential, **named):
    enums = dict(zip(sequential, range(len(sequential))), **named)
    return type('Enum', (), enums)
Numbers = enum('ZERO', 'ONE', 'TWO')
# Numbers.ZERO == 0 and Numbers.ONE == 1

 

有带值到名称映射的:

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def enum(*sequential, **named):
    enums = dict(zip(sequential, range(len(sequential))), **named)
    reverse = dict((value, key) for key, value in enums.iteritems())
    enums['reverse_mapping'] = reverse
    return type('Enum', (), enums)
# Numbers.reverse_mapping['three'] == 'THREE'

 

有用set实现的:

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class Enum(set):
    def __getattr__(self, name):
        if name in self:
            return name
        raise AttributeError
Animals = Enum(["DOG", "CAT", "HORSE"])
print Animals.DOG

 

有用range实现的:

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dog, cat, rabbit = range(3)
# or
class Stationary:
    (Pen, Pencil, Eraser) = range(0, 3)
print Stationary.Pen

 

有用tuple实现的:

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class Enum(tuple): __getattr__ = tuple.index
State = Enum(['Unclaimed', 'Claimed'])
print State.Claimed

 

有用namedtuple实现的:

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from collections import namedtuple
def enum(*keys):
    return namedtuple('Enum', keys)(*keys)
MyEnum = enum('FOO', 'BAR', 'BAZ')
# 带字符数字映射的,像C/C++
def enum(*keys):
    return namedtuple('Enum', keys)(*range(len(keys)))
# 带字典映射的,可以映射出各种类型,不局限于数字
def enum(**kwargs):
    return namedtuple('Enum', kwargs.keys())(*kwargs.values())

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