>>> import enum
>>> bool(enum.Enum)
False
>>> bool(enum.IntEnum)
False

This behaviour is relatively unexpected for classes, and can lead to subtle bugs such as the following:

https://bitbucket.org/ambv/singledispatch/issues/8/inconsistent-hierarchy-with-enum

I guess it's marked 2.7 because of the enum34 backport? There's no enum in the 2.7 stdlib.

I believe this was brought up before on one of the lists but I don't recall the outcome of the discussion, except that for IntEnum the behavior is correct.  I tend to agree that for plain Enum it's a problem, the question is whether we can fix it without breaking code that accidentally relies on this behavior.

Oh wait. The *class* is False-y? That's definitely a bug, just fix it.

Yes, I didn't find a separate bug tracker for the enum34 backport, which is why I included that version here.

> for IntEnum the behavior is correct

Do you remember the argument? I agree that IntEnum *instances* may be falsy, but IntEnum classes I don't see why.

That said, if an IntEnum *class* has to be false-y, then there's no real point in fixing just Enum (you can pass an IntEnum instance to singledispatch() too).

Ok, we posted at the same time :-) Yes, the class is false-y.

Just reading the code now, the reason is that EnumMeta pretends to be a collection (it defines a __len__ and an __iter__).

EnumMeta /is/ a collection (at least in the same sense the dict class is a collection).  ;)

Fix is on it's way...

See also issue23008.

New changeset 772805538caf by Ethan Furman in branch '3.4':
Issue26748: Enum classes should evaluate as True
https://hg.python.org/cpython/rev/772805538caf

New changeset f840608f79da by Ethan Furman in branch '3.5':
Issue26748: Enum classes should evaluate as True
https://hg.python.org/cpython/rev/f840608f79da

New changeset 2fc61f8ee2d2 by Ethan Furman in branch 'default':
Issue26748: Enum classes should evaluate as True
https://hg.python.org/cpython/rev/2fc61f8ee2d2

Enum classes are now Truth-y in 3.4, 3.5, enum34, and aenum.  :)