grid in pygame

BLACK = (0, 0, 0)
WHITE = (200, 200, 200)
WINDOW_HEIGHT = 400
WINDOW_WIDTH = 400


def main():
    global SCREEN, CLOCK
    pygame.init()
    SCREEN = pygame.display.set_mode((WINDOW_HEIGHT, WINDOW_WIDTH))
    CLOCK = pygame.time.Clock()
    SCREEN.fill(BLACK)

    while True:
        drawGrid()
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                pygame.quit()
                sys.exit()

        pygame.display.update()


def drawGrid():
    blockSize = 20 #Set the size of the grid block
    for x in range(WINDOW_WIDTH):
        for y in range(WINDOW_HEIGHT):
            rect = pygame.Rect(x*blockSize, y*blockSize,
                               blockSize, blockSize)
            pygame.draw.rect(SCREEN, WHITE, rect, 1)