import graphics as gr
SIZE_X = 400
SIZE_Y = 400
window = gr.GraphWin("Model", SIZE_X, SIZE_Y)
#  Начальное положение шарика
coords = gr.Point(200, 200)
#  Скорость
velocity = gr.Point(1, -1)
def add(point_1, point_2):
    new_point = gr.Point(point_1.x + point_2.x,
                      point_1.y + point_2.y)
    return new_point
def draw_circle(coords):
    circle = gr.Circle(coords, 10)
    circle.setFill('red')
    circle.draw(window)
while True:
    draw_circle(coords)
    coords = add(coords, velocity)

 def add(point_1, point_2):
    new_point = gr.Point(point_1.x + point_2.x,
                      point_1.y + point_2.y)

     new_point = gr.Point(point_1.x + point_2.x,
                      point_1.y + point_2.y)