[Python-Dev] Floor division

[Gareth McCaughan]

On Wednesday 24 January 2007 10:20, Alexey Borzenkov wrote:

> > > I think that's the right thing to do, because that is mathematically
> > > correct. j is just an imaginary number with a property that j*j = -1.
> > > So
> > >
> > > (a+bj) + (c+dj)j = (a-d) + (b+c)j.
> >
> > Yes, thanks, I know what j is, and I know how to multiply
> > complex numbers. (All of which you could have deduced from
> > reading what I wrote, as it happens.) The question is whether
> > it makes sense to define complex(a,b) = a+ib for all a,b
> > or whether the two-argument form is always in practice going
> > to be used with real numbers[1]. If it is, which seems pretty
> > plausible to me, then changing complex() to complain when
> > passed two complex numbers would (1) notify users sooner
> > when they have errors in their programs, (2) simplify the
> > code, and (3) avoid the arguably broken behaviour Tim was
> > remarking on, where complex(-0.0).real is +0 instead of -0.
>
> Haven't looked in source code for complex constructor yet, but I think that
> if it changes sign of -0.0 then it just does something wrong and needs
> fixing without change in behaviour. Maybe it could check if numbers it got
> on input are real or complex and proceed accordingly so that it never gets
> to computing -0.0-(+0.0), i.e. when second argument is not a complex number
> it could just add it to imaginary part of first argument, but skip
> substracting inexistant 0.0 from first argument's real part. Change of
> behaviour like ignoring imaginary part of second argument seems bad to me,
> and that's my only point. Besides, documentation (at least for Python 2.4)
> clearly states that second argument can be a complex number:

I'm not suggesting that it should ignore the imaginary part of
the second argument, and I don't think anyone else is either.
What might make sense is for passing a complex second argument
to raise an exception.

(I don't particularly object to the present behaviour either.)

The fact that the documentation states explicitly that the
second argument can be a complex number is probably sufficient
reason for not changing the behaviour, at least before 3.0.

-- 
g