Mark Dickinson added the comment: Terry: can you clarify which part you think is potentially confusing? I'm having a hard time seeing the text as confusing, but I suspect I'm too close to the subject matter to be able to tell.
Charles: I think you're missing the point (which does rather reinforce Terry's suggestion that this FAQ could be improved). You say: > "-190 % 12 == -10 is wrong according to the C definition for computer modulo > arithmetic." But that's the point: for C (specifically C99[*]), -10 is the *correct* result from the operation -190 % 12. And that's exactly why this is a FAQ: Python is behaving differently from many other mainstream languages (C, Java, C++, C#, ...) here, so it's useful to understand the justification for this design decision. For C in particular, this behaviour is mandated by section 6.5.5p6 of C99, which reads: > When integers are divided, the result of the / operator is the algebraic > quotient with any fractional part discarded. If the quotient a/b is > representable, the expression (a/b)*b + a%b shall equal a. The first part of this forces -190 / 12 to be -15 (the result of discarding the fractional part of the true quotient -15.833....); the second then forces -190 % 12 to be (-190) - (-15)*12, which is -10. ([*] In C89, the rounding direction of a/b for negative a, and hence the behaviour of a%b, was left implementation defined, but same-sign-as-a appears to have been the dominant behaviour.) ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue31021> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
