import pygame, sys
from pygame.locals import *

BLACK = (0, 0, 0)
WHITE = (255, 255, 255)
RED = (255, 0, 0)
GREEN = (0, 255, 0)
BLUE = (0, 0, 255)

x = 200
y = 200
sx = 1
sy = 1

pygame.init()
windowSurface = pygame.display.set_mode((600, 400), 0, 32)
pygame.display.set_caption("Pallopeli")

while True:
    pygame.draw.circle(windowSurface, BLACK, (x-sx, y-sy), 10)
    if y >= 400 or y <= 0:
        sy *= -1

    if x >= 600 or x <= 0:
        sx *= -1

    x += sx
    y += sy

    pygame.draw.circle(windowSurface, WHITE, (x, y), 10)
    pygame.display.update()

while True:
    for event in pygame.event.get():
        if event.type == QUIT:
            pygame.quit()
            sys.exit()