如何构造一个不区分大小写的枚举？

我有一个简单的 Python 2.7 枚举：

from enum import Enum

class Label(enum):
    RedApple = 1
    GreenApple = 2

我希望能够使用不区分大小写的键创建枚举对象：

fruitname = "redapple"
a = Label[fruitname]

我尝试创建一个__init__ method:

def __init__(self, key):
    super(Label, self).__init__()
    pass # do comparison here

但我不断遇到错误：

super(Label, self).__init__()
NameError: global name 'Label' is not defined

我想做一个比较key.lower().strip()。这可能吗？

In Python 3.6 and aenum 2.0 https://pypi.python.org/pypi/aenum¹² (which is compatible with 2.7 and 3.0+) a new method has been added: _missing_².

该方法在之前调用ValueError引发是为了让自定义代码有机会尝试找到枚举成员by value。不幸的是，这使得它不适合您的用例——按名称查找。

Fortunately, aenum has the extra option of defining a _missing_name_ method³ which will be called when name lookup fails.

您上面的代码应如下所示：

from aenum import Enum

class Label(Enum):

    RedApple = 1
    GreenApple = 2

    @classmethod
    def _missing_name_(cls, name):
        for member in cls:
            if member.name.lower() == name.lower():
                return member

并在使用中：

>>> Label['redapple']
<Label.RedApple: 1>

如果卡住使用 3.6 stdlib（或想要与其保持兼容），您可以 (ab)使用_missing_ but:

• 你必须做Label('redapple')相反（圆括号，而不是方括号），并且
• 您将反对枚举的设计（“redapple”是名称，而不是值）

¹ Disclosure: I am the author of the Python stdlib Enum https://docs.python.org/3/library/enum.html, the enum34 backport https://pypi.python.org/pypi/enum34, and the Advanced Enumeration (aenum) https://pypi.python.org/pypi/aenum library.

² enum34 https://pypi.python.org/pypi/enum34 does not have these improvements as it is only being maintained for bug fixes.

³ _missing_value_ is preferred in aenum as it is more explicit about what it is checking, but it falls back to _missing_ for compatibility with the stdlib.

⁴ aenum v2.0.2 has a bug where _missing_ is called for both values and names if _missing_name_ has not been overridden -- this is fixed in v2.0.3+.