from tkinter import *

def make_grid(canv, w, h, cell_size):
    for x in range(cell_size, w, cell_size):
        canv.create_line(x, 0, x, h, fill="#FFFF00")


def L_pressed(event):
    print(event.x, event.y)

master = Tk()
WIDTH = 800
HEIGHT = 700
CELL_SIZE = 50
C = Canvas(master, width=WIDTH, height=HEIGHT, bg='#000000')

C.bind('<Button-1>', L_pressed)

make_grid(C, WIDTH, HEIGHT, CELL_SIZE)
C.pack()

mainloop()