Set angle to self.Angle - 10*dt???
Why not just self.Angle - 10 ?
dt is the time that passed between the current tick and the former tick, by setting every tick the angle to self.angle - 10* dt, you make it change every tick with a speed of 10*dt degrees per frame, which translates to an average speed of 10 degrees per seconds regardless of the framerate.
if it was just self.angle-10 then it would change not only faster, but alsodepending on the framerate (twice as fast on a screen with a 120Hz refresh rate compared to a 60 Hz one, also would be slower if the game was having a hard time rendering every frame on a regular basis)
hope that helps