bool(Enum) should raise ValueError

[Ethan Furman]

On 07/26/2019 11:56 AM, Erik Aronesty wrote:

> I just spend a while tracking down and killing all "if Enum" and "if not
> Enum" bugs in my code.   I was frankly shocked that this didn't raise a
> ValueError to begin with.

Very few items, if any, raise a ValueError when asked for its True/False equivalence.

> Apparently all enums are true/false depending on whether the underlying
> value is truthy or falsy.

That is the default.  You can, of course, change that:

   class AlwaysFalse(Enum):
       def __bool__(self):
           return False

   class AlwaysTrue(Enum):
       def __bool__(self):
           return True

> Which breaks the abstraction Enum's are trying to achieve because now the
> user of an Enum has to know "stuff" about the underlying value and how it
> behaves.

You can make it always fail:

   class OnTheFence(Enum):
       def __bool__(self):
           raise ValueError('%s members are neither True nor False' % self.__class__.__name__)

The default Enum always returns True because the default Enum starts counting at 1.

Perhaps you could share your Enum definition and what you expected to happen when you used it in a boolean context?

--
~Ethan~