Enumeration idioms: Values from different enumerations

[Peter Hansen]

Ben Finney wrote:
> These are valid concerns. I can't see how to reconcile these against
> the desire for values from different enums to fail comparison.
> 
> Am I alone in my tri-state view of enumeration value comparisons? Can
> anyone else defend why values from different enumerations should not
> compare?

While I'm largely a disinterested bystander, it occurs to me that if you 
look at the reasons behind wanting enumerations in the first place, you 
might find a good reason to defend this view.

For example, if enumerations are intended to reduce the likelihood of 
certain types of errors (where the use of typical XXXX=3 "constants" 
might be more prone to errors), then perhaps this suggests that passing 
errors silently is bad.  That is, trying to compare enumerations that 
should not be compared *is* an error (raising an exception) *because* 
the whole point of enumerations is to avoid errors in such cases.

Or perhaps I'm off the mark as to why people want enumerations.  Is it 
just a cosmetic consideration?  (Yes, I've used and appreciated them 
extensively in C and might even pick up Enum for my Python code... I'm 
just sort of playing devil's advocate here.)

-Peter