It's true that a*(b/c) yields fractions which would probably accrue accuracy errors depending on how those values are implemented. For example, it is possible to represent 1/3 internally as two numbers, numerator and denominator, thus avoiding the repeating decimal (or binimal, or whatever it's called). I believe there are languages that preserve exact accuracy in this way for rational fractions. I don't know if Python is one of them.
On the other hand, (a*b)/c is safer since in this case (for the binomial coefficient) it always yields an integer. -= m =- On Friday, August 26, 2016 at 1:42:31 AM UTC-7, Christian Gollwitzer wrote: > Am 26.08.16 um 09:53 schrieb Erik: > > On 26/08/16 08:44, mlz wrote: > >> Here's the key: > >> > >> $ python2 > >> Python 2.7.10 ... > >>>>> 1/2 > >> 0 > >>>>> > >> > >> $ python > >> Python 3.5.1 ... > >>>>> 1/2 > >> 0.5 > >>>>> 1//2 > >> 0 > >>>>> > >> > >> I read about this awhile ago, but it's not until it bites you that you > >> remember fully. > > > > How is this related to your question? The example explicitly says Python > > 2 and doesn't use the '//' operator. > > > > It's related by the fact that a*b/c performs integer division (intended > by the OP) which gives a different result than a*(b/c) (unintended by > the OP). Floating point (as in Python 3) *also* may give a different > result, but the deviation from the "true", i.e. mathematical value, is > far less than with integer arithmetics. > > Christian -- https://mail.python.org/mailman/listinfo/python-list
