"MRAB" <pyt...@mrabarnett.plus.com> wrote in message news:mailman.3158.1247667680.8015.python-l...@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. -- http://mail.python.org/mailman/listinfo/python-list
