Greater and less than operators [was Re: [Tutor] beginning to code]

[Steven D'Aprano]

On Tue, 19 Sep 2017 17:26:55 -0700, Rick Johnson wrote:

> Of course, allowing all objects to use the `==`, `!=` sugars makes
> perfect sense, but `<`, `>`, `<=`, `>=` are meaningless outside of
> numeric-ish types.


You've never wanted to sort strings? How do you sort strings unless you 
have a concept of which string comes before the other, i.e. < operator?

>>> 'xyz' < 'abc'
False


Same applies to lists of items. Provided the items are compatible with 
ordering, so are the lists. Likewise other sequences.

And for that matter, sets. Maybe we'd prefer to use the proper 
mathematical operators ⊂ and ⊃ for subset and superset, but a good ASCII 
equivalent would be < and > instead.

Likewise, any time you want to express some sort of order relationship:

pawn < rook < knight < bishop < queen < king

perhaps. (Although, in real games of chess, the value of a piece partly 
depends on what other pieces are left on the board.)

Or perhaps you have some sort of custom DSL (Domain Specific Language) 
where > and < make handy symbols for something completely unrelated to 
ordering:

cake > oven  # put cake into the oven

cake < oven  # remove cake from oven


I don't mean that as a serious example of a useful DSL. But it is the 
kind of thing we might want to do. Only hopefully less lame.



-- 
Steven D'Aprano
“You are deluded if you think software engineers who can't write 
operating systems or applications without security holes, can write 
virtualization layers without security holes.” —Theo de Raadt