Case-insensitive string equality

[Rick Johnson]

Steven D'Aprano wrote:
[...]
> (1) Add a new string method, which performs a case-
> insensitive equality test. Here is a potential
> implementation, written in pure Python:
> 
> def equal(self, other):
>     if self is other:
>         return True
>     if not isinstance(other, str):
>         raise TypeError
>     if len(self) != len(other):
>         return False
>     casefold = str.casefold
>     for a, b in zip(self, other):
>         if casefold(a) != casefold(b):
>             return False
>     return True
> 
> Alternatively: how about a === triple-equals operator to do
> the same thing?

A good idea. But wouldn't that specific usage be
inconsistent (even backwards) with the semantics of "===" as
defined in most languages that use "==="?

For me -- and this comment will be going beyond the scope of
strings, and possibly, beyond the scope of this thread -- i
feel that python is missing a pair of equality testing
devices (sugared or not; but preferably sugared), that
define a universal means by which all types can be tested
with either "superficial equality" (aka: ==) or "deep
equality" (aka: ===).

However, such a design (whist quite intuitive) would break
equality testing as it exists today in Python. For instance,
it would mean that:


(1) Superficial Equality
    
    >>> "abc" == "abc"
    True
    >>> "abc" == "ABC" 
    True
 
(2) Deep Equality
     
     >>> "abc" === "abc"
     True
     >>> "abc" === "ABC"
     False
     
And i don't think even GvR's time machine will be much
help here. :-(