grid in pygame

1BLACK = (0, 0, 0)
2WHITE = (200, 200, 200)
3WINDOW_HEIGHT = 400
4WINDOW_WIDTH = 400
5
6
7def main():
8    global SCREEN, CLOCK
9    pygame.init()
10    SCREEN = pygame.display.set_mode((WINDOW_HEIGHT, WINDOW_WIDTH))
11    CLOCK = pygame.time.Clock()
12    SCREEN.fill(BLACK)
13
14    while True:
15        drawGrid()
16        for event in pygame.event.get():
17            if event.type == pygame.QUIT:
18                pygame.quit()
19                sys.exit()
20
21        pygame.display.update()
22
23
24def drawGrid():
25    blockSize = 20 #Set the size of the grid block
26    for x in range(WINDOW_WIDTH):
27        for y in range(WINDOW_HEIGHT):
28            rect = pygame.Rect(x*blockSize, y*blockSize,
29                               blockSize, blockSize)
30            pygame.draw.rect(SCREEN, WHITE, rect, 1)