python如何方向键控制上下左右

bif="1.jpg" 
mif="2.jpg" 
import pygame,sys 
from pygame.locals import * 
 
pygame.init() 
 
screen=pygame.display.set_mode((640,360),0,32) 
background=pygame.image.load(bif).convert() 
mouse_c=pygame.image.load(mif).convert_alpha() 
 
x,y=0,0 
movex,movey=0,0 
 
while True: 
  for event in pygame.event.get(): 
    if event.type ==QUIT: 
      pygame.quit() 
      sys.exit() 
    if event.type==KEYDOWN: 
      if event.key==K_LEFT: 
        movex=-1 
      if event.key==K_RIGHT: 
        movex=+1 
      elif event.key==K_UP: 
        movey=-1 
      elif event.key==K_DOWN: 
        movey=+1 
    if event.type==KEYUP: 
      if event.key==K_LEFT: 
        movex=0 
      if event.key==K_RIGHT: 
        movex=0 
      elif event.key==K_UP: 
        movey=0 
      elif event.key==K_DOWN: 
        movey=0 
 
  x+=movex 
  y+=movey 
   
  screen.blit(background,(0,0)) 
  screen.blit(mouse_c,(x,y)) 
   
  pygame.display.update()