[Python-Dev] Boolean transition (original) (raw)

Paul Prescod paul@prescod.net
Sun, 10 Mar 2002 17:51:44 -0800

Guido van Rossum wrote:

... 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.

Agree 100%. The question is whether five years or ten years or twenty years from now booleans will still be a subtype of integers. We have deprecation techniques that allow us to start a transition to a world where logic and integer arithmetic are completely separate.

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.

I agree with this too. The question is whether Python 3000 will still allow this without error:

def foo(int_size, b_metric_unit): if b_metric_unit: return int_size * 10

foo(false, 10)

I would say that one day (not tomorrow!) the multiplication of a boolean should raise an assertion as nonsensical.

Paul Prescod