Kristján V. Jónsson schrieb: > Hm, doesn´t seem to be so for my regular python. > > maybe it is 2.3.3, or maybe it is stackless from back then. It's because you are using Windows. The way -0.0 gets rendered depends on the platform. As Tim points out, try math.atan2(0.0, -0.0) vs math.atan2(0.0, 0.0). Regards, Martin