import pygame

pygame.init()
screen = pygame.display.set_mode((400, 300))
done = False
clock = pygame.time.Clock()

x = 30
y = 30

def time_slice(time_since, interval):
        "return current time slice"
        return int(time_since / interval)

interval = 10 # second
time_since = 0 # second
last_slice = 0
time_passed = 1

def image(path):
        return pygame.image.load(path).convert_alpha()

while not done:
        for event in pygame.event.get():
                if event.type == pygame.QUIT:
                        done = True

        pressed = pygame.key.get_pressed()
        if time_slice(time_since, interval) != last_slice:
                if pressed[pygame.K_w]:
                        y -= 20
                elif pressed[pygame.K_s]:
                         y += 20
                elif pressed[pygame.K_a]:
                        x -= 20
                elif pressed[pygame.K_d]:
                        x += 20

                last_slice = time_slice(time_since, interval)
        time_since += time_passed

        screen.fill((255, 255, 255))


        screen.blit(image('man.png'), (x, y))

        pygame.display.flip()
        clock.tick(60)