On Fri, May 7, 2010 at 9:19 AM, Xavier Ho <contact@xavierho.com> wrote:
2010/5/7 spir ☣ <denis.spir@gmail.com>
The following discussion in the article does not tell whether one solution is the _official_ one. But: that -4/3 != -(4/3) looks simply wrong for me.
Denis
I believe the official decision relates to PEP 238:
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)... [...] 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. -- Mark