import tkinter

canvas = tkinter.Canvas(width="640", height="480")
canvas.pack()
square = canvas.create_rectangle(250, 250, 300, 300, fill="green")
direction = 1
def movement():
    global direction
    x1, y1, x2, y2 = canvas.coords(square)
    print(x1, y1, x2, y2)
    if y1 < 0:
        direction = 1
    if y2 > 480:
        direction = -1
    canvas.move(square, 0, (direction * 3))
    canvas.after(50, movement)


canvas.bind("<Button-1>", movement)
canvas.mainloop()