On Tue, Feb 15, 2011 at 3:49 PM, Hans-Peter Jansen <h...@urpla.net> wrote: > Hi, > > while I usually cope with the woes of floating point issues, this is > one, that I didn't expect: > >>>> round(2.385, 2) > 2.3799999999999999 > > Doesn't the docs say, it's rounded up for this case? > > <quote> > Values are rounded to the closest multiple of 10 to the power minus n; > if two multiples are equally close, rounding is done away from 0 > </quote> > > Well, that one is clearly rounding down. > > What's up, eh, down here?
http://docs.python.org/library/functions.html#round : """ Note: The behavior of round() for floats can be surprising: for example, round(2.675, 2) gives 2.67 instead of the expected 2.68. This is not a bug: it’s a result of the fact that most decimal fractions can’t be represented exactly as a float. See "Floating Point Arithmetic: Issues and Limitations"[1] for more information. """ [1]: http://docs.python.org/tutorial/floatingpoint.html And indeed: >>> from decimal import Decimal >>> Decimal(2.385) Decimal('2.3849999999999997868371792719699442386627197265625') Which, rounded to 2 decimal places, gives us 2.38, which is in turn approximated as: 2.37999999999999989341858963598497211933135986328125 I encourage reading [1]. Cheers, Chris -- http://blog.rebertia.com -- http://mail.python.org/mailman/listinfo/python-list
