import pygame
import sys

pygame.init ()
screen = pygame.display.set_mode((400, 300  ))

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

while True:
    events = pygame.event.get ()
    for event in events:
        if event.type == pygame.QUIT:
            pygame.quit ()
            sys.quit ()
    screen.blit (surface, (175, 125))
    pygame.display.update ()