Does Python need an 'xor' operator?

[logistix]

>
> Ahhhh!!!  that's a GREAT idea!  That way, you could write
> something like:
>

It gets a little trickier though.  Here's the real reason for short-circuit
evaulation:

>>> a = 1
>>> a or c
1
>>> c or a
Traceback (most recent call last):
  File "<interactive input>", line 1, in ?
NameError: name 'c' is not defined
>>>

So you can write stuff like:

if isinstance(a, foo) and a.fooOnlyValue:
    pass

instead of the less clear

if isinstance(a, foo):
    if a.fooOnlyValue:
        pass

without throwing an error.  Returning the actual values is more of a side
effect than anything.  So then the next question is, Are non-existant values
considered False or should they throw an error?

If they're false, it looks like you need to incorporate eval's into the
function wrapped with try/except statments to work properly. Some people
don't seem to like doing things like that for some reason ;)