[Edu-sig] Strange results
Hello! My friend noticed strange results from Python 2.5.2: >>> b=47 >>> 0-b/2 -23 >>> -b/2+0 -24 Anybody can explain that? Regards, Andrzej Kapanowski ___ Edu-sig mailing list Edu-sig@python.org http://mail.python.org/mailman/listinfo/edu-sig
Re: [Edu-sig] Strange results
On Tue, Jan 3, 2012 at 2:23 AM, Andrzej Kapanowski wrote: > Hello! > > My friend noticed strange results from Python 2.5.2: > b=47 0-b/2 > -23 -b/2+0 > -24 > > Anybody can explain that? > It's integer division: >>> -1/2 -1 >>> 1/2 0 Not symmetrical. Why? http://www.peterbe.com/Integer-division-in-programming-languages Helps some maybe. Kirby > Regards, > Andrzej Kapanowski > > > ___ > Edu-sig mailing list > Edu-sig@python.org > http://mail.python.org/mailman/listinfo/edu-sig > ___ Edu-sig mailing list Edu-sig@python.org http://mail.python.org/mailman/listinfo/edu-sig
Re: [Edu-sig] Strange results
Hi, apart from integer-division (see Kirby's post) the result also depends on different interpretations of the operator "-": My friend noticed strange results from Python 2.5.2: >>> b=47 >>> 0-b/2 -23 is interpreted as 0 - ( b/2) so integer division comes first before subtraction (- as subtraction operator). >>> -b/2+0 -24 is interpreted like ( (-1) * b ) / 2 + 0 so a leading - is applied like a _multiplication_ and because * and / are on equal levels of execution, the left-most is evaluated first. Always interesting how seemingly simple and "straightforward" rules can trip you in special circumstances. Parentheses are recommended if you want to be sure. Happy new year Christian Anybody can explain that? Regards, Andrzej Kapanowski ___ Edu-sig mailing list Edu-sig@python.org http://mail.python.org/mailman/listinfo/edu-sig ___ Edu-sig mailing list Edu-sig@python.org http://mail.python.org/mailman/listinfo/edu-sig
