There is an announcement button but it shows undefined

I created a page for playing videos, there is a button to play videos, and there is a button to switch the screen， There is also a video playback button on the second page， But the problem is if the play key of the second page is empty (I will trigger the event annotation)， The program can be executed and the screen switches smoothly But once there's something in there he will show undefined

import sys,random,math,pygame
import time
from pygame.locals import *
from moviepy.editor import *

def button(screen, position, text, size, colors="white on blue"):
    fg, bg = colors.split(" on ")
    font = pygame.font.SysFont("Arial", size)
    text_render = font.render(text, 1, fg)
    x, y, w , h = text_render.get_rect()
    x, y = position
    pygame.draw.line(screen, (150, 150, 150), (x, y), (x + w , y), 5)
    pygame.draw.line(screen, (150, 150, 150), (x, y - 2), (x, y + h), 5)
    pygame.draw.line(screen, (50, 50, 50), (x, y + h), (x + w , y + h), 5)
    pygame.draw.line(screen, (50, 50, 50), (x + w , y+h), [x + w , y], 5)
    pygame.draw.rect(screen, bg, (x, y, w , h))
#     print(screen.blit(text_render, (x, y)))
    return screen.blit(text_render, (x, y))

pygame.init()
window = pygame.display.set_mode((1400,700))
pygame.display.set_caption('影片播放測試')
font = pygame.font.Font('aa.ttf',50)
window.fill((120,120,120))
pygame.display.flip()

sys_start = False
sys2 =False

b1 = button(window, (650, 400), "game start", 50, "white on green")
b2 = button(window, (650, 500), "game off", 50, "red on yellow")

while True:
    
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            pygame.QUIT  
         
        pygame.display.update() 
        
        if event.type == pygame.MOUSEBUTTONDOWN:
            
            if b2.collidepoint(pygame.mouse.get_pos()):
                pygame.quit()
#            開始     
            elif b1.collidepoint(pygame.mouse.get_pos()):
                sys_start = True
            
            elif b3.collidepoint(pygame.mouse.get_pos()):
#                 videomode = pygame.display.set_mode((1400,700))
                pygame.display.set_caption('Hello World!')
                print("即將撥放影片")
                clip = VideoFileClip('1-1test.mp4')
                clip.preview()

            #the problem is here    
            elif b5.collidepoint(pygame.mouse.get_pos()):
                pygame.display.set_caption('Hello World!')
                print("即將撥放影片")
                clip = VideoFileClip('1-1test.mp4')
                clip.preview()
                
            elif b22.collidepoint(pygame.mouse.get_pos()):
                sys_start = False
                sys2 = True
            
            elif b27.collidepoint(pygame.mouse.get_pos()):
                sys2 = False
                sys_start = True
               
        
            
        if sys_start == True:
#             print('影片播放')
            window.fill((120,120,120))
            b3 = button(window, (390, 400), "playvideo", 50, "white on green")
            b22 = button(window, (1350, 350), ">", 50, "white on red")
            pygame.display.update()
        
        if sys2 == True:
#             print('影片播放')
            window.fill((120,120,120))
            b5 = button(window, (390, 400), "playvideo2", 50, "white on green")
            b27 = button(window, (0, 350), "<", 50, "white on red")
            pygame.display.update()
        

I marked the problematic part, Hope you guys can help me