code: def angle2d(self):
          
          if self.x==0:
              if   self.y<0:  return       math.pi/2.0*3
              elif self.y>0:  return       math.pi/2.0
              else:           return 0
          elif self.y==0:
              if   self.x<0:  return       math.pi
             #elif self.x>0:  return 0
              else:           return 0
          ans = math.atan( self.y / self.x )
          if self.x > 0:
              if self.y>0:    return ans
              else:           return ans + math.pi*2.0
          else:               return ans + math.pi
docs: determine the angle of this point on a circle, measured in radians (presume values represent a Vector)