[Python-Dev] PEP 435 -- Adding an Enum type to the Python standard library

Ethan Furman ethan at stoneleaf.us
Sat Apr 27 04:09:15 CEST 2013

On 04/26/2013 06:37 PM, Greg Ewing wrote:
> Eli Bendersky wrote:
>> There's a conceptual difference between a value of an enumeration and a collection of such values.
> Not if you think of an enum as a type and a type as
> defining a set of values. From that point of view, the
> enum itself is already a collection of values, and
> introducing another object is creating an artificial
> distinction.

I agree (FWIW ;).

It seems to me that the closest existing Python data type is bool.

bool is a type and has exactly two members, which are static/singleton/only created once.

Enum is a metatype which we use to create a type with a fixed number of members which are static/singleton/only created 

The salient differences:

   with Enum we name the type and the members
   with Enum the members are also attributes of the type

As a concrete example, consider:

class WeekDay(Enum):
     SUNDAY = 1
     MONDAY = 2
     TUESDAY = 3
     WEDNESDAY = 4
     THURSDAY = 5
     FRIDAY = 6
     SATURDAY = 7

If we follow bool's example, then like True and False are of type(bool), TUESDAY should be of type(WeekDay).


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