python-3.x - Python中的一组常量

Question

我想要这样的东西:

class Fruits:
   APPLE = 'APPLE'
   ORANGE = 'ORANGE'
   MANGO = 'MANGO'

# I want to access members easily
print(Fruits.APPLE)

# I want to list all members
print(list(Fruits))

# I want to check if a string belongs to the set
print('POTATO' in Fruits)

我想要纯字符串常量，分组到一个类中:

• 成员(member)检查
• 列出所有值

Python 枚举似乎不适合，因为:

• 枚举不是普通字符串，引入一种新类型
• 枚举需要使用.value
• 不能直接序列化，否则很笨拙。

这可以用 Python 实现吗？我想为此我可能需要一些神奇的方法或元类？

Answer 1

如果您想自己实现，可以使用 元类 和 __iter__ 方法。

class Meta(type):
    def __new__(cls, name, bases, dct):
        # this just iterates through the class dict and removes
        # all the dunder methods
        cls.members = [v for k, v in dct.items() if not k.startswith('__') and not callable(v)]
        return super().__new__(cls, name, bases, dct)
    
    # giving your class an __iter__ method gives you membership checking
    # and the ability to easily convert to another iterable
    def __iter__(cls):
        yield from cls.members

class Fruits(metaclass=Meta):
    APPLE = 'APPLE'
    ORANGE = 'ORANGE'
    MANGO = 'MANGO'


print(Fruits.APPLE)
print('APPLE' in Fruits)
print(list(Fruits))