In article <mailman.96.1430761253.12865.python-l...@python.org>, Chris Angelico <ros...@gmail.com> wrote: >On Tue, May 5, 2015 at 3:32 AM, Irmen de Jong <irmen.nos...@xs4all.nl> wrote: >> That is a broad question, but one thing that comes to mind is the >current (python 3) >> behavior of integer division. It gives the exact result and doesn't >truncate to integers: >> >> >>>>> 5/4 >> 1.25 > >Using the word "exact" around non-integer values can be a little >ambiguous, since floats are often inexact. But yes, int/int -> float, >and yes, it WILL bite C programmers.
This should not be presented as a somewhat arbitrary decision. Formerly we had 3e0/4e0 0.75 and 3/4 0 So the / operator worked on reals giving reals and integers giving integers. Great if you're used to it, but sometimes a pitfall. Also in practice it sometimes leads to rounding in unexpected places. The greatest disadvantage is when you have i and j and want their ratio. You have to do something like (real)i/j which feels unnatural. So we need two different division operators on the integers. Solution: introduce // for integer by integer given integer, giving the quotient (with a possible remainder). Now / is free to be used for the more rational "i/j gives a ratio", i.e. a real number. Bottom line 3e0/4e0 and 3/4 gives the same result. It is nice to no longer have to be very careful in floating point calculation to avoid integer constants. On the other hand integer division is still available to solve the familiar egg-farm problems: I have 103 eggs. 12 eggs go in a box. How many boxes can I fill? (Similar problems crop up in graphics all the time.) > >ChrisA Groetjes Albert -- Albert van der Horst, UTRECHT,THE NETHERLANDS Economic growth -- being exponential -- ultimately falters. albert@spe&ar&c.xs4all.nl &=n http://home.hccnet.nl/a.w.m.van.der.horst -- https://mail.python.org/mailman/listinfo/python-list
