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.)