Enum with only a single member

[Steven D'Aprano]

Is it silly to create an enumeration with only a single member? That is, a 
singleton enum?

from enum import Enum

class Unique(Enum):
    FOO = auto()


The reason I ask is that I have two functions that take an enum argument. The 
first takes one of three enums:

class MarxBros(Enum):
    GROUCHO = 1
    CHICO = 2
    HARPO = 3

and the second takes *either* one of those three, or a fourth distinct value. 
So in my two functions, I have something like this:


def spam(arg):
    if isinstance(arg, MarxBros): 
        ...


def ham(arg):
    if isinstance(arg, MarxBros) or arg is Unique.FOO:
        ...


Good, bad or indifferent?



-- 
Steven
"Ever since I learned about confirmation bias, I've been seeing 
it everywhere." - Jon Ronson