[Python-Dev] Boolean transition

[Guido van Rossum]

[PP]
> If you're arguing that booleans should be subtypes of integers
> because integers can be used in a boolean context then I guess
> booleans should ALSO be subtypes of strings and lists because
> strings and lists can also be used in a boolean fashion.

I don't know about others, but *my* arguments for making bool a
subtype of int has *nothing* to do with the fact that ints can be used
in a bool context.  (That would be reversing the inheritance, as you
point out.)  It is rather the opposite: bool values gotten from
certain operations (e.g. comparisons, and most built-in predicate
functions) are commonly used in int contexts, because they are
currently represented by 0 and 1.  So the constraint under which we're
operating is that bool values must be ints.  This constraint has only
two possible solutions: (a) continue to use int as the type of choice
for bool results, and define builtins False = 0 and True = 1; or (b)
make bool a subtype of int.

I do not want to say that in the future only bool is acceptable in a
Boolean context; it would remove too many of my favorite ways of
expression things clearly with few words.  That's my final word on
this particular subissue.

--Guido van Rossum (home page: http://www.python.org/~guido/)