'Set the Pie/Doughnut chart rotation: the angle of the first slice.
Args:
rotation: First segment angle: 0 <= rotation <= 360.
Returns:
Nothing.'

def set_rotation(self, rotation):

    if (rotation is None):
        return
    if ((rotation < 0) or (rotation > 360)):
        warn(('Chart    rotation    %d    outside    Excel    range:    0    <=    rotation    <=    360' % rotation))
        return
    self.rotation = int(rotation)
