Why is my Pygame game loop inefficient and causing incorrect blitting?

Why is my Pygame application loop not working properly?

Your main game loop is incorrect, which is causing your Pygame application to malfunction. Here's a breakdown of the issues:

Issues in the Main Application Loop

Incorrect Blitting Order:

In your code, you attempt to blit the background at the position of an object and then move the object before blitting it at its new position. This is unnecessary. The background should be drawn once at the beginning of each frame, and objects should be blitted on top of it without erasing the previous position.

Modified Main Application Loop

Here's a corrected version of your main application loop:

while True:

    # Handle events
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit()

    # Update objects (based on input and frames)
    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT]:
        screen.blit(background, objects[0].pos, objects[0].pos)
        objects[0].move_left()
        screen.blit(objects[0].image, objects[0].pos)  # Blit object at new position
    if keys[pygame.K_RIGHT]:
        screen.blit(background, objects[0].pos, objects[0].pos)
        objects[0].move_right()
        screen.blit(objects[0].image, objects[0].pos)  # Blit object at new position
    if keys[pygame.K_UP]:
        screen.blit(background, objects[0].pos, objects[0].pos)
        objects[0].move_up()
        screen.blit(objects[0].image, objects[0].pos)  # Blit object at new position
    if keys[pygame.K_DOWN]:
        screen.blit(background, objects[0].pos, objects[0].pos)
        objects[0].move_down()
        screen.blit(objects[0].image, objects[0].pos)  # Blit object at new position

    for num in range(num_objects - 1):
        objects[num + 1].rand_move()

    # Draw background
    screen.blit(background, (0, 0))

    # Draw scene
    for o in objects:
        screen.blit(o.image, o.pos)

    # Update display
    pygame.display.update()
    pygame.time.delay(100)

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