[Python-Dev] PEP 285: Adding a bool type

[David Abrahams]

----- Original Message -----
From: "Guido van Rossum" <guido@python.org>
To: "David Abrahams" <david.abrahams@rcn.com>
Cc: <python-list@python.org>; <python-dev@python.org>
Sent: Saturday, March 30, 2002 8:47 AM
Subject: Re: [Python-Dev] PEP 285: Adding a bool type


> [David Abrahams]
> >       6) Should we eventually remove the inheritance relationship
> >          between Int and Bool?
> >
> > I hope so. Bool is-a Int doesn't seem like the right relationship to
> > me, unless perhaps we make Int is-a Long... naah, not even then.
>
> Hm.  In your favorite language bool is one of the integral types.
> Doesn't that imply pretty much the same thing?

Well, I try not to play favorites <0.002 wink>, but the implicit
conversion rules in C++ are admittedly and unfortunately liberal.
However, bool is detectably NOT derived from int in C++:

    void f(int const&);
    f(false); // error!
    assert(boost::is_base_and_derived<int,bool>::value); // fails!

> Anyway, do you have a use case where it matters?

Given that Bool is immutable, I have no cases other than examples of
type introspection which can be written to account for the fact that
Bool is-a Int. However, it does make certain things trickier to get
right:

numeric_types = [ Int, Long, Bool, Float, Complex ]
for t in numeric_types:
    if isinstance(x, t):
        # Do something...

This sort of thing could depend on getting the order of the list right
(I didn't).

-Dave