numeric emulation and the rich comparison operators
gagsl-py2 at yahoo.com.ar
Fri Jul 11 11:24:03 CEST 2008
En Thu, 10 Jul 2008 17:37:42 -0300, Ethan Furman <ethan at stoneleaf.us>
> 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
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.
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