simple_enum.py

"""
Usage:

>>> class Color(SimpleEnum):
>>>     red = KV
>>>     green = 'green'  # same as using `KV`
>>>     grey = 'gray'
>>> Color.red
'red'
>>> Color.grey
'gray'
>>> Color.keys()
['red', 'green', 'grey']
>>> Color.values()
['red', 'green', 'gray']

Actually, built-in `enum.Enum` could achieve the same thing:

>>> class Color(enum.Enum):
>>>     red = 'red'
>>>     green = 'green'
>>>     grey = 'gray'
>>> Color.__members__.keys()
odict_keys(['red', 'green', 'grey'])
>>> list(Color.__members__.keys())
['red', 'green', 'grey']
>>> Color._member_names_
['red', 'green', 'grey']
>>> [i.value for i in Color]
['red', 'green', 'gray']
>>> list(Color._value2member_map_)
['red', 'green', 'gray']

Just not that intuitive and convenient tho.
"""

from six import with_metaclass


KV = type('KV', (object, ), {})


class SimpleEnumMeta(type):
    def __new__(mcs, name, bases, attrs):
        keys = []
        values = []
        for k, v in attrs.items():
            if k.startswith('_'):
                continue
            if v is KV:
                v = k
                attrs[k] = v
            keys.append(k)
            values.append(v)
        attrs['_keys'] = keys
        attrs['_values'] = values
        return type.__new__(mcs, name, bases, attrs)


class SimpleEnum(with_metaclass(SimpleEnumMeta, object)):
    @classmethod
    def keys(cls):
        return cls._keys

    @classmethod
    def values(cls):
        return cls._values

    @classmethod
    def items(cls):
        return zip(cls._keys, cls._values)