import pygame

# --- constanst --- (UPPER_CASE_NAMES)

RED = (255, 0, 0)
BLACK = (0, 0, 0)

WIDHT = 500
HEIGHT = 500

# --- main ---

speed = 10

pygame.init()

window = pygame.display.set_mode((WIDHT, HEIGHT))

item = pygame.Rect(0, 0, 50, 50)
item.centery = HEIGHT//2

clock = pygame.time.Clock()
running = True
while running:

    # - events -

    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    # - updates - (without draws)

    item.x += speed

    if item.right >= WIDHT:
        speed = -speed
    if item.left <= 0:
        speed = -speed

    # - draws - (without updates)

    window.fill(BLACK)
    pygame.draw.rect(window, RED, item, 2)
    pygame.display.update()

    clock.tick(60)

# - end -
pygame.quit()