import pygame

pygame.init()

screen = pygame.display.set_mode((640, 480))
pygame.display.set_caption("Arrow Keys")
clock = pygame.time.Clock()

BG   = (20, 20, 20)
RED  = (220, 60, 60)

RADIUS = 25
x = 320.0
y = 240.0
speed = 5

running = True
while running:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT]:
        x -= speed
    if keys[pygame.K_RIGHT]:
        x += speed
    if keys[pygame.K_UP]:
        y -= speed
    if keys[pygame.K_DOWN]:
        y += speed

    if x < -RADIUS:
        x = 640 + RADIUS
    elif x > 640 + RADIUS:
        x = -RADIUS

    if y < -RADIUS:
        y = 480 + RADIUS
    elif y > 480 + RADIUS:
        y = -RADIUS

    screen.fill(BG)
    pygame.draw.circle(screen, RED, (int(x), int(y)), RADIUS)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()