求大神帮忙看看为什么没有出现字

1. import sys, random, time, pygame
   
2. from pygame.locals import *
   
3. 
   
4. def print_text(font, x, y, text, color=(255,255,255)):
   
5.     imgText = fon.render(text, True, color)
   
6.     screen.blit(imgText, (x,y))
   
7. 
   
8. pygame.init()
   
9. screen = pygame.display.set_mode((600,500))
   
10. pygame.display.set_caption("测试你的打字速度")
    
11. font1 = pygame.font.Font(None, 24)
    
12. font2 = pygame.font.Font(None, 200)
    
13. white = 255,255,255
    
14. yellow = 255,255,0
    
15. 
    
16. key_flag = False
    
17. correct_answer = 97
    
18. seconds = 11
    
19. score = 0
    
20. clock_start = 0
    
21. game_over = True
    
22. 
    
23. while True:
    
24.     for event in pygame.event.get():
    
25.         if event.type == QUIT:
    
26.             sys.exit()
    
27.         elif event.type == KEYDOWN:
    
28.             key_flag = True
    
29.         elif event.type == KEYUP:
    
30.             key_flag = False
    
31. 
    
32.         keys = pygame.key.get_pressed()
    
33.         if keys[K_ESCAPE]:
    
34.             sys.exit()
    
35.             
    
36.         if keys[K_RETURN]:
    
37.             if game_over:
    
38.                 game_over = False
    
39.                 score = 0
    
40.                 seconds = 11
    
41. clock_start = time.clock()
    
42. current = time.clock() - clock_start
    
43. speed = score * 6
    
44. if seconds-current < 0:
    
45.     game_over = True
    
46. elif current <= 10:
    
47.     if keys[correct_answer]:
    
48.         correct_answer = random.randint(97,122)
    
49.         score += 1
    
50. 
    
51. screen.fill((0,100,0))
    
52. 
    
53. print_text(font1, 0, 0, "让我们看看你打字有多快！")
    
54. print_text(font1, 0, 20, "尽量保持10秒钟……")
    
55. 
    
56. if key_flag:
    
57.     print_text(font1, 500, 0, "<用计算机键盘输入>")
    
58. 
    
59. if not game_over:
    
60.     print_text(font1, 0, 80, "时间: " + str(int(seconds-current)))
    
61. 
    
62. print_text(font1, 0, 100, "速度: " + str(speed) + "字母/分钟")
    
63. 
    
64. if game_over:
    
65.     print_text(font1, 0, 160, "按回车键开始……")
    
66. 
    
67. print_text(font2, 0, 240, chr(correct_answer-32), yellow)
    
68. 
    
69. pygame.display.update()
    
70. 
    

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没有人吗