Falsey Enums

[Pavol Lisy]

On 7/28/17, Steve D'Aprano <steve+python at pearwood.info> wrote:
> On Fri, 28 Jul 2017 05:52 pm, Ethan Furman wrote:
>
>> class X(Enum):
>>      Falsey = 0
>>      Truthy = 1
>>      Fakey = 2
>>      def __bool__(self):
>>          return bool(self.value)
>
> Thanks Ethan.

BTW bool at enum seems to be expensive:

%timeit 7 if x else 0
850 ns ± 12.9 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

%timeit 7 if x.value else 0
479 ns ± 4.38 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

%timeit 7 if x!=X.Falsey else 0
213 ns ± 10.6 ns per loop (mean ± std. dev. of 7 runs, 1000000 loops each)

> Like Ben, I'm surprised that's not the default behaviour.

Me too.

I was trying to find some example which is not completely semantically
wrong and where backward compatibility is important.

Maybe something like this? ->

class Color(Enum):
    black = 0  # this could equal to some external library constant
value for black
    white = 0xff

color = user_choice()

if not color:  # color is None
   color = random.choice(list(Color))