为什么会出现“此代码无法访问”，求解

def print_text(font,x,y,text,color=(255,255,255)):
    imgText=font.render(text,True,color)
    screen.blit(imgText,(x,y))

pygame.init()
screen=pygame.display.set_mode((600,500))
pygame.display.set_caption("Mouse Demo")
font1=pygame.font.Font(None,24)
white=255,255,255
mouse_x=mouse_y=0
move_x=move_y=0
mouse_down=mouse_up=0
mouse_down_x=mouse_down_y=0
mouse_up_x=mouse_up_y=0

while True:
    for event in pygame.event.get():
        if event.type==QUIT:
            sys.exit()
        if event.type==MOUSEMOTION:
            mouse_x,mouse_y=event.pos
            move_x,move_y=event.rel
        elif event.type==MOUSEBUTTONDOWN:
            mouse_down=event.button
            mouse_down_x,mouse_down_y=event.pos
        elif event.type==MOUSEBUTTONUP:
            mouse_up=event.button
            mouse_up_x,mouse_up_y=event.pos

keys=pygame.mouse.get_pressed()
if keys[K_ESCAPE]:
    sys.exit()
    screen.fill((0,100,0))
    print_text(font,0,0,"Mouse Events")
    print_text(font1,0,20,"Mouse position:"+str(mouse_x)+","+str(mouse_y))
    print_text(font,0,40,"Mouse relative:"+str(move_x)+","+str(move_y))
    print_text(font1,0,60,"Mouse button down:"+","+str(mouse_down)+"at"+str(mouse_down_x)+","+str(mouse_down_y))
    print_text(font1,0,80,"Mouse button up:"+","+str(mouse_up)+"at"+str(mouse_up_x)+","+str(mouse_up_y))
    print_text(font1,0,160,"Mouse Polling")
    x,y=pygame.mouse.get_pos()
    print_text(fon1,0,180,"Mouse position:"+str(x)+","+str(y))
    b1,b2,b3=pygame.mouse.get_pressed()
    print_text(font1,0,200,"Mouse buttons:"+str(b1)+","+str(b2)+","+str(b3))
pygame.display.update()

是按照原代码输的吗？如果是，那keys=...那里开始缩进错了，screen.fill也是，接在exit后面