# Strange results

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## Strange results

 Hello!My friend noticed strange results from Python 2.5.2:>>> b=47>>> 0-b/2-23>>> -b/2+0-24Anybody can explain that?Regards,Andrzej Kapanowski _______________________________________________ Edu-sig mailing list [hidden email] http://mail.python.org/mailman/listinfo/edu-sig
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## Re: Strange results

 On Tue, Jan 3, 2012 at 2:23 AM, Andrzej Kapanowski <[hidden email]> 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-languagesHelps some maybe. Kirby > Regards, > Andrzej Kapanowski > > > _______________________________________________ > Edu-sig mailing list > [hidden email] > http://mail.python.org/mailman/listinfo/edu-sig> _______________________________________________ Edu-sig mailing list [hidden email] http://mail.python.org/mailman/listinfo/edu-sig
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## Re: Strange results

 In reply to this post by Andrzej Kapanowski 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 > [hidden email] > http://mail.python.org/mailman/listinfo/edu-sig_______________________________________________ Edu-sig mailing list [hidden email] http://mail.python.org/mailman/listinfo/edu-sig
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