On Thu, May 6, 2010 at 17:43, Mathias Panzenböck < grosser.meister.morti@gmx.net> wrote:
Shouldn't by by mathematical definition -x // y be the same as -(x // y)? But when assign x=2, y=3 you get:
-2 // 3 -1 -(2 // 3) 0
And also:
2 // -3 -1 -2 // -3 0
And even more:
int(-2 / 3) 0 int(2 / -3) 0
I think this rather odd. Is there any deeper reason to this behaviour? I guess changing this will break a lot of code, but why does it behave like this?
Operator precedence; unary negation (the 'factor' rule from Grammar/Grammar) binds more tightly than // (the 'term' rule), thus applying the negation to '2' before applying the '//'. Making it bind as `-(x // y)` would require introducing a special grammar rule just to make sure that unary negation on binary operators like this worked this way. And I am not even sure if that would be unambiguous in Python's LL(1) grammar. -Brett
-panzi
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