[Numpy-discussion] ufunc oddities

[Robert Kern]

On Sat, May 24, 2008 at 9:45 PM, Charles R Harris
<charlesr.harris at gmail.com> wrote:
>> I'm not sure why you're showing me numpy C code. I am talking about
>> the Python bools True and False.
>
> Because I'm talking about ufuncs. The original question was about ufuncs
> and, since array booleans are not treated as numbers for ordinary
> arithmetic, the question was when *do* we treat them as numbers. I'm a
> bugger for consistency and booleans aren't consistent.

And I brought up the Python bools because there is a relationship that
numpy has with the rest of Python's types that we need to keep in
mind.

I think it boils down to this: when we have places where bools are
operated with bools and expect to output bools, we can decide what the
rules are. For the arithmetic operations +-*, there are reasonable
Boolean logic interpretations that we can apply.

When upcasting is requested, either implicitly or explicitly, they
turn into 1s and 0s. All of the behaviors you think are inconsistent
just arise from the consistent application of that simple rule. Since
it *is* sometimes useful to treat booleans as numerical 1s and 0s, I
think it would be a mistake to prevent it. Sure, it doesn't really
make sense to do sin(True), but if you want to preserve the useful
behaviors, you will just end up with a big list of special cases and
make behavior difficult to reason about.

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
 -- Umberto Eco