On Fri, May 7, 2010 at 7:43 PM, Mark Dickinson <dickinsm@gmail.com> wrote:
No: PEP 238 is (partly) about how integer division is expressed in Python; not about its semantics. Python's choice for integer division with negative arguments goes back much further. From Misc/HISTORY:
================================== ==> RELEASE 0.9.6 (6 Apr 1992) <== ==================================
[...]
New features in 0.9.6:
[...]
- Division and modulo for long and plain integers with negative operands have changed; a/b is now floor(float(a)/float(b)) and a%b is defined as a-(a/b)*b. So now the outcome of divmod(a,b) is the same as (a/b, a%b) for integers. For floats, % is also changed, but of course / is unchanged, and divmod(x,y) does not yield (x/y, x%y)... [...]
Nice! Thanks for sharing.
Personally, I've always liked Python's behaviour in this regard: for the few times that I've needed an 'x % y' operation that works with both positive and negative x, more often than not x-y*floor(x/y) turns out to be what I need. I've lost count of the number times I've had to write something awkward like:
/* adjust for the exponent; first reduce it modulo _PyHASH_BITS */ e = e >= 0 ? e % _PyHASH_BITS : _PyHASH_BITS-1-((-1-e) % _PyHASH_BITS);
in C.
Wow. I would never write code like that, but you got a fair point. Cheers, Xav (Mark: Sorry, I forgot to reply to the correct list.)