numeric emulation and the rich comparison operators

[Ethan Furman]

Gabriel Genellina wrote:
> En Thu, 10 Jul 2008 17:37:42 -0300, Ethan Furman <ethan at stoneleaf.us>  
> escribi�:
> 
>> Greetings, List!
>>
>> Still working on my Measure class, and my next question is... (drum 
>> roll  please ;)
>>
>> What are the advantages of using __[eq|ne|lt|gt|le|ge]__ vs __cmp__?
> 
> 
> If your objects obey the trichotomy law (an object MUST BE less than,  
> greater than, or equal to another one, and there is no other 
> possibility)  then __cmp__ is enough, and easier to define than all the 
> rich comparison  operations.
> In other cases, __cmp__ is not suitable: by example, complex numbers 
> can't  define "greater than" [in a way that preserves the meaning for 
> real  numbers]; you can only use "equal" or "not equal". You can't use 
> __cmp__  for this, because it *has* to return either >0 or <0 (implying 
> "greater  than" or "less than"). In this case it's best to use the rich 
> comparison  operators: define __eq__ and __ne__ and make all other 
> comparisons between  complex numbers raise an exception.
> 

That's exactly the information I needed.  Thanks!