grid.py

import pygame

WIDTH = 800
WIN = pygame.display.set_mode((WIDTH, WIDTH))
GREY = (128, 128, 128)

def draw_grid(win, width):
    square_count = 50
    square_size = width // square_count
    for i in range(square_count):
        pygame.draw.line(win, GREY, (0, i*square_size), (width, i*square_size))
        pygame.draw.line(win, GREY, (i*square_size, 0), (i*square_size, width))
    pygame.display.update()

run = True
square_count = 50

draw_grid(WIN, WIDTH)
while run:
    for event in pygame.event.get():
            if event.type == pygame.QUIT:
                run = False