Enums: making a single enum

[Steven D'Aprano]

On Sat, 26 May 2018 18:14:08 +1000, Chris Angelico wrote:

> On Sat, May 26, 2018 at 6:00 PM, Steven D'Aprano
> <steve+comp.lang.python at pearwood.info> wrote:
>> Actually I don't really need all the features of Enums, I might just
>> define my own class:
>>
>>
>> class Maybe:
>>      def __repr__(self):
>>          return "Maybe"
>>
>> Maybe = Maybe()
>>
>>
>>
>> I wish there was a simpler way to define symbols with identity but no
>> state or behaviour...
> 
> You DO have behaviour though - the repr is a behaviour of that object.
> So what you have there (reusing the name for the instance) seems decent
> to me.

I *just knew* some clever Dick (or clever Chris in this case...) would 
point out that repr is behaviour. Technically you are correct (the best 
kind of correct...) but in a practical sense we don't really count having 
a repr as behaviour. All objects ought to have a repr: calling print(obj) 
or displaying the object in the REPL shouldn't raise an exception. Even 
None has a repr :-)

I want an easy way to make new objects like None and NotImplemented 
without having to explicitly define a class first. Some languages make 
that real easy (although the semantics might not be quite identical):

    Ruby                :Maybe
    Javascript          Symbol("Maybe")
    Julia               :Maybe or Symbol("Maybe")
    Scala               'Maybe
    Elixir              :Maybe
    Erland              maybe or 'Maybe'


Elixir and Erland call them atoms; Erland also requires them to begin 
with a lowercase letter, otherwise they must be surrounded by single 
quotes.


Hey-Chris-you-want-to-collaborate-on-a-PEP-for-this-ly y'rs,


-- 
Steve