Usefulness of the "not in" operator

[candide]

Le 08/10/2011 12:50, Jon Clements a écrit :

> 10 - 5 as 10 + -5 (as obviously the - is redundant as an operation),
> and 10 / 2 as int(10 * .5) or something, who needs a divide!?



OK, I see your point but I was supposing non-membershipness seldom 
needed and in fact one can suppose that test membership is heavily more 
used than test non-membership.

In fact, it seems that most Python operators have an "antonym" operator, 
for instance :

== vs !=
< vs >=
is vs is not
+ vs -

etc