At 08:31 AM 3/20/2007, you wrote: >On Tue, Mar 20, 2007 at 04:09:49AM -0700, Dick Moores wrote: > > At 11:00 AM 3/19/2007, Michael Hannon wrote: > > >On Mon, Mar 19, 2007 at 03:04:03AM -0700, Dick Moores wrote: > > >> Yesterday I was shocked, SHOCKED, to discover that round() is > > >> occasionally rounding incorrectly. For example, > > >> > > >> >>> print round(0.19945,4) > > >> 0.1994 > > >. > > >. > > >. > > >> Comments, Tutors? Am I way out in left field with this? > > > > > > > > >I suggest you might want to look at the discussion of unbiased > rounding at: > > > > > > http://en.wikipedia.org/wiki/Rounding > > > > Thanks. I'm familiar with "unbiased rounding". I'm glad to know about > > that Wikipedia article. Could you tell me what, in particular, you > > wanted me to think about? > >Well, perhaps this is something for me to think about, but if you had asked >me to round 0.19945 to four decimal places, I would have told you the answer >is 0.1994, i.e., the same answer that Python gives.
Is this because that rounding conforms to "unbiased rounding"? If so, then you won't like >>> print round(0.19965, 4) 0.1997 (which rounds up to an odd number, 7) But after thinking about it, I may revise my round2() function to do "unbiased rounding". It appeals to me, even though most of my life I've used what the Wikipedia article terms "the common method": ===================================================== This method is commonly used, for example in accounting. It is the one generally taught in basic mathematics classes. This method is also known as Symmetric Arithmetic Rounding or Round-Half-Up (Symmetric Implementation): Decide which is the last digit to keep. Increase it by 1 if the next digit is 5 or more (this is called rounding up) Leave it the same if the next digit is 4 or less (this is called rounding down) ======================================================= Dick Moores _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
