Previous screen is not clearing in pygame

Question

Here I'm trying move which is blotted on the screen but the image moving without clearing the previous one

balloon=pygame.image.load("BALLON 1".png)
Bal_x=0
       
while true:
    for event in pygame.event.get():
        if event.type==pygame.QUIT:
            pygame.quit()
            sys.exit()
    Bal_x+=1
    screen.blit(BALLON,(Bal_x.120))
    pygame.display.update()
    clock.tick(120)

It moves like in the image

Answer 1

You have to clear the display with pygame.Surface.fill in every frame:

balloon=pygame.image.load("BALLON 1".png)
Bal_x=0
       
while true:
    for event in pygame.event.get():
        if event.type==pygame.QUIT:
            pygame.quit()
            sys.exit()
    Bal_x+=1

    screen.fill((0, 0, 0)) # <--- this is missing

    screen.blit(BALLON,(Bal_x.120))
    pygame.display.update()
    clock.tick(120)

The typical PyGame application loop has to:

• handle the events by calling either pygame.event.pump() or pygame.event.get().
• update the game states and positions of objects dependent on the input events and time (respectively frames)
• clear the entire display or draw the background
• draw the entire scene (blit all the objects)
• update the display by calling either pygame.display.update() or pygame.display.flip()
• limit the frames per second to limit CPU usage with pygame.time.Clock.tick