[Python-ideas] PEP for enum library type?

[Ethan Furman]

On 02/12/2013 07:31 AM, Antoine Pitrou wrote:
> Le Tue, 12 Feb 2013 07:21:04 -0800,
> Eli Bendersky <eliben at gmail.com> a écrit :
>>
>> from enum import Enum
>>
>> class Color(Enum):
>>    RED, BLUE, GREEN
>
> I think I'd favour a namedtuple-style approach, e.g.:
>
> class Color(Enum):
>      fields = ('RED', 'BLUE', 'GREEN')
>
> (which allows you to build enums programmatically too)
>
> Also, I think you have to provide several classes, at least
> SequenceEnum and StringEnum, and perhaps also BitmaskEnum.
> It makes sense for them to be separate types, 1) because it makes it
> explicit how the given enum behaves, 2) because combining integer and
> str constants in an enum would be crazy.

I partially agree with Antoine; there should be three types of Enum 
available:

    - sequence (most common: 0, 1, 2, 3, etc.)
    - flag (1, 2, 4, 8, etc.)
    - unique ('on', 'off'; 'north', 'south', 'east', 'west')

and they shouldn't be mixed together higgledy-piggledy in the same class.

However, I like the simplicity of Tim's approach.

The result of the implementation I've been playing with looks something 
like:

class Color(Enum):
     type = 'sequence'
     RED, GREEN, BLUE

class Geometry(Enum):
     type = 'unique'
     LEFT, RIGHT, TOP, BOTTOM
     WEST, EAST, NORTH, SOUTH

class FieldType(Enum):
     type = 'flag'
     BINARY, AUTOINC, NULLABLE


The metaclass takes care of assigning the next value and selecting the 
proper subclass; 'unique' values are lower-cased (LEFT -> 'left'); 
subclassing is possible; and each Enum value is properly an instance of 
it's Enum class.

One important reason for having the different types of Enum is for 
prototyping.

--
~Ethan~