Are you talking about the fact that the player isn't buffered correctly. I used a pink square as my "you sprite". This line you are talking about is probably what Eck has mentioned.
Now I am not familiar with python/pygame (remember I downloaded it last time to help you ) but..
I'd say you call this after updating display: pygame.display.flip()
Also, put your code in code blocks next time to it's easier for other people to help you. Just click on the < > button that appears in the editor menu and paste your code in there, selecting the generic code option.
EDIT: That didn't work, i'll check what other functions are available ^^
Found the problem : You need to fill the screen with a color after you draw to it to "reset" it basically. So right after you do your display.update, add this:
screen.fill(pygame.Color(0, 0, 0, 255))
This just fills the room with black.