On Tue, Sep 1, 2015 at 12:59 PM, Tim Peters <tim.peters@gmail.com> wrote:

...

I was under the impression that such cases are to be considered bugs. I know it was a driving concern in the implementation of the enum module.

Sorry, I just had to laugh at the notion that enums _could_ be implemented in such a convoluted way that there'd ever be the slightest possibility of transitivity failing ;-)

Easy: you just declare that different enumerations are not comparable,, but that all are comparable to their base type. class Color(IntEnum): RED=1 GREEN=2 BLUE=3 class Permission(IntEnum): READ=1 WRITE=2 EXECUTE=3 What should Color.RED==Permission.READ give? True, because they're both 1? False, because they're completely different things? TypeError, because you can't logically compare colors and permissions? If you allow that Color.RED==1 (which you need to if it's going to be possible to backwardly-compatibly change raw numbers into an enum), then transitivity demands that the otherwise-illogical comparison above succeed, and be True. As a design decision, it could viably be taken either way, but once taken, it has to be maintained forever. ChrisA