[Tutor] toggle idiom?

[Paul Sidorsky]

Sean 'Shaleh' Perry wrote:

> > is the best way of writing the original code because it clearly
> > shows the logic (as apposed to arithmetic) intent of the operation and
> > works for all cases the original works for.  The only reason for using
> > the original instead of this is if a must be 0 or 1 in the end, rather
> > than simply a false or true value.
> 
> is there a case where 'a = not a' will yield a value other than 0 or 1?  i am
> not aware of one.

Neither am I, and furthermore the new boolean type coming in for 2.3
will have True == 1 and False == 0.  This strongly suggests that not
False == True == 1 is already the norm, as is not <nonzero> == False ==
0.  If this wasn't the case then old code could break when the boolean
type is introduced, and avoiding that was a key concern (see PEP 285).

I can't see any problem with a = not a.  It's been used in C for years,
perhaps decades.  In fact the only other reasonable alternative I've
seen is using C's ternary ?: operator (a = a ? 0 : 1) which is really
just a short form of what the OP already had, but since Python has no ?:
or equivalent this isn't an option.

-- 
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Paul Sidorsky                                          Calgary, Canada
paulsid@shaw.ca                        http://members.shaw.ca/paulsid/