Simple Tic-Tac-Toe using tkinter

I've been learning programming using a book about Python for a few months. To explore object-oriented programming, I built a few things in tkinter.

When I started this code, I wanted to be able to play on rectangular boards of any sizes, but it made checking for a winner more difficult, so it's just the regular 3x3 game at the moment.

How can I improve it?

```
from tkinter import *

# PARAMETERS
# graphics
WINDOW_SIZE = 600 # pixels
GRID_LINE_WIDTH = 2 # pixels
SYMBOL_WIDTH = WINDOW_SIZE/12 # pixels - adjust ratio

# 0-1 : size of a symbol relative to it's cell
# bigger than 1 is too much
SYMBOL_SIZE = 0.5

X_COLOR = 'dodger blue'
O_COLOR = 'tomato'
# background color of the 'draw' gameover screen
DRAW_SCREEN_COLOR = 'light sea green'
GRID_COLOR = 'light grey'
BG_COLOR = 'white'

# gameplay
FIRST_PLAYER = 2 # 1 - X, 2 = O

# OTHER
CELL_SIZE = WINDOW_SIZE / 3

# game states
STATE_TITLE_SCREEN = 0
STATE_X_TURN = 1
STATE_O_TURN = 2
STATE_GAME_OVER = 3

# symbol notation in the board memory
EMPTY = 0
X = 1
O = 2

class Game(Tk):
"""
Main class
"""
def __init__(self):
Tk.__init__(self)
self.canvas = Canvas(
height=WINDOW_SIZE, width=WINDOW_SIZE,
bg=BG_COLOR)

self.canvas.pack()

self.bind('', self.exit)
self.canvas.bind('', self.click)

self.gamestate = STATE_TITLE_SCREEN
self.title_screen()

self.board = [
[EMPTY, EMPTY, EMPTY],
[EMPTY, EMPTY, EMPTY],
[EMPTY, EMPTY, EMPTY]]

def title_screen(self):
# placeholder title screen
self.canvas.delete('all') #just in case

self.canvas.create_rectangle(
0, 0,
WINDOW_SIZE, WINDOW_SIZE,
fill=O_COLOR,
outline='')

self.canvas.create_rectangle(
int(WINDOW_SIZE/15), int(WINDOW_SIZE/15),
int(WINDOW_SIZE14/15), int(WINDOW_SIZE14/15),
width=int(WINDOW_SIZE/20),
outlin

As a small suggestion, I noticed that your Os have an odd line at the right hand side due to drawing them with the outline of an oval (as you noticed and commented in the draw_O function). You can fix that by instead using two filled ovals, a big one which is filled using O_COLOR and a smaller one filled using BG_COLOR (Although this does require adjusting the delta to compensate for the missing width):

def draw_O(self, grid_x, grid_y):
    """
    draw an O symbol at x, y in the grid
    note : a big outline value appears to cause a visual glitch in tkinter
    """
    x = self.gtpix(grid_x)
    y = self.gtpix(grid_y)
    delta = 1.5*CELL_SIZE/2*SYMBOL_SIZE
    self.canvas.create_oval(
        x-delta, y-delta,
        x+delta, y+delta,
        fill = O_COLOR, outline="")
    self.canvas.create_oval(
        x-delta/3, y-delta/3,
        x+delta/3, y+delta/3,
        fill = BG_COLOR, outline="")

Note the now missing artifact:

StackExchange Code Review Q#155692, answer score: 4