This is my code and it works, but I don't know why my previous code didn't work. there was no error showed when I tried my previously written code. if I simply changed 'SysFont' into 'Font', an error would show, saying no such file, so I copied the ttf file into the application folder and it worked just fine.
fontObj4 =pygame.font.Font("seguisym.ttf",30)
textSurfaceObj4 = fontObj4.render('Press arrow '+ u'\u2191'+' '+u'\u2193'+ ' level now: %d' % diff2, True,BLACK)
My previous code:
fontObj4 =pygame.font.SysFont("seguisym.ttf",30)
textSurfaceObj4 = fontObj4.render('Press arrow '+ u'\u2191'+' '+u'\u2193'+ ' level now: %d' % diff2, True,BLACK)