Why is my Pygame application loop not updating correctly?

Why is my pygame application loop not working properly?

Upon examining your provided code, it appears that the loop arrangement is the primary issue. In your main application, you are attempting to erase portions of the screen and redraw them for each entity, while only redrawing the specific entity in its updated position. This approach is not necessary and can lead to visual inconsistencies.

In general, the best practice is to:

1. Clear the entire display or draw the background.
2. Redraw all entities on top of it.
3. Update the display.

In this revised code snippet, we have rearranged the loop as mentioned above:

while 1:

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

    # update objects (depends on input events and frames)
    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT]:
        objects[0].move_left()    
    if keys[pygame.K_RIGHT]:
        objects[0].move_right()
    if keys[pygame.K_UP]:
        objects[0].move_up()
    if keys[pygame.K_DOWN]:
        objects[0].move_down()

    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 dispaly
    pygame.display.update()
    pygame.time.delay(100)

This loop now effectively clears the screen, draws all entities, and then updates the display each frame.

Refer to this minimal example for further clarification:

[Example Link]

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