missing 'xor' Boolean operator

[MRAB]

Steven D'Aprano wrote:
> On Tue, 14 Jul 2009 11:25:08 -0700, Dr. Phillip M. Feldman wrote:
> 
>> Current Boolean operators are 'and', 'or', and 'not'.  It would be nice
>> to have an 'xor' operator as well.
> 
> I've often wished there was too, for the sake of completeness and 
> aesthetics, I'd love to be able to write:
> 
> a xor b
> 
> instead of defining a function xor(a, b).
> 
> Unfortunately, outside of boolean algebra and simulating electrical 
> circuits, I can't think of any use-cases for an xor operator. Do you have 
> any?
> 
The problem is that 'and' and 'or' are not limited to Boolean values:

     'and' returns the first false value or the last true value.

     'or' returns the first true value or the last false value.

What values should 'xor' return? IMHO, if only one of the values is true
then it should return that value, otherwise it should return False.

     1 xor 0 => 1
     0 xor 2 => 2
     1 xor 2 => False
     0 xor 0 => False

This is because it's a Boolean operator, so it should fall back to
Boolean values when necessary, like 'not':

     not 0 => True
     not 1 => False

Also:

     x and y and z => (x and y) and z
     x or y or z => (x or y) or z

therefore:

     x xor y xor z => (x xor y) xor z