Pygame Issue with importing a rectangle for a game

Question

I have a small question about placing a rectangle in pygame. When I run the code i dont see a rectangle. Does anyone knows how to fix this?

import pygame as pg
from pygame.locals import *

pg.init()

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


size = width, height = (800, 800)
screen = pg.display.set_mode(size)
pg.display.set_caption("Ball Game")
screen.fill((10, 255, 255))
pg.display.update()
running = True
clock = pg.time.Clock()

#board = pg.draw.rect(screen, BLACK, pg.Rect(30, 30, 60, 60))
#board_loc = pg.
#board_loc.center = width/2, height*0.8

background_image = pg.image.load("pngtree-blue-cartoon-minimalist-planet-surface-starry-sky-main-map-background-image_186868.jpg").convert()

while running:
    for event in pg.event.get():
        if event.type == QUIT:
            running = False
    screen.blit(background_image, [0, 0])
    pg.display.flip()
    #screen.blit(board, board_loc)
    rect = pg.Rect(0, 0, 200, 100)
    rect.center = (300, 300)
    pg.draw.rect(screen, BLACK, rect)


clock.tick(30)
pg.quit()

enter image description here

Answer 1

You have to update the display after drawing the rectangle:

rect = pg.Rect(0, 0, 200, 100)
rect.center = (300, 300)

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

    # draw background
    screen.blit(background_image, [0, 0])
   
    # draw rectangle on top of the background 
    pg.draw.rect(screen, BLACK, rect)

    # update display
    pg.display.flip()

You are actually drawing on a Surface object. If you draw on the Surface associated to the PyGame display, this is not immediately visible in the display. The changes become visible, when the display is updated with either pygame.display.update() or pygame.display.flip().