import pygame, sys

pygame.init()
display = pygame.display.set_mode((400,300))
background = pygame.Surface((400,300))

surface = pygame.Surface((50,50))
surface.fill((0,255,0))

pos = [175,125]

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.quit()
            sys.exit()
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_RIGHT:
                pos[0] += 20
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                pos[0] += -20
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_UP:
                pos[1] += -20
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_DOWN:
                pos[1] += 20

    display.blit(background, (0,0))
    display.blit(surface, pos)
    pygame.display.update()