code: def add_coord(self, x, y):
          
          x = x*self.x_factor
          y = y*self.y_factor
          self.plotData.add_coord(x, y)
          self.circles_list.append(gui.SvgCircle(x, y, self.circle_radius))
          self.append(self.circles_list[-1])
          if len(self.circles_list) > self.maxlen:
              self.remove_child(self.circles_list[0])
              del self.circles_list[0]
docs: Adds a coord to the polyline and creates another circle