[Python-Dev] A proposal has surfaced on comp.lang.python to r edefine "is"

[Gareth McCaughan]

Peter Norvig wrote:

> Let me point out that in Common Lisp, there are five equality 
> predicates:
> 
>   eq     like Python's 'is', only true for identical objects
>   eql    also true for numbers with same value

Numbers and characters; characters as well as numbers
may behave counterintuitively w.r.t EQ.

>   equal  like Python's '=='
>   equalp also true for strings with different case
>   =      only works on numbers, true if they are eql after
>          conversion to the same type

Ha. Don't forget

    char=        only works on characters, equivalent to EQL then
    char-equal   only works on characters, ignores case
    string=      only works on strings, equivalent to EQUAL then
    string-equal only works on strings, ignores case

> I would say that Python is served well by the two equality predicates
> it has, that it is impossible to please everyone, and that users
> should get used to writing the predicate they want if it is not one of
> the builtins.

Agreed. Although the fact that EQL is much more useful in practice
than EQ suggests that there's something to be said for making Python's
"is" more EQL-like. (Not enough, in my opinion, to make it worth doing.)

-- 
g