missing 'xor' Boolean operator

Bill Davy Bill at SynectixLtd.com
Wed Jul 15 16:37:54 CEST 2009


"MRAB" <python at mrabarnett.plus.com> wrote in message 
news:mailman.3158.1247667680.8015.python-list at python.org...
> 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


Gosh, let's all discuss commutation and distribution.

And surely in quantum merchanics there is something about non-commuting 
operatiomns letting in Planck's constant. 





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