pygame elipse has gone wrong : I am trying to make a simple pygame Tic Tac Toe game. the following code is not finished. all its supposed to do is to draw a 3*3 grid, where each rectangle is filled with a red X and a green ellipse.
    import pygame
import random
from pygame.locals import *


    table = [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
    
    # Define some colors
    BLACK = (0, 0, 0)
    WHITE = (255, 255, 255)
    GREEN = (0, 255, 0)
    RED = (255, 0, 0)
    BLUE = (0, 0, 255)

    pygame.init()

    # Set the width and height of the screen [width, height]
    window_size = [500, 500]
    screen = pygame.display.set_mode(window_size, HWSURFACE | DOUBLEBUF | 
    RESIZABLE)

    pygame.display.set_caption("My Game")

    # Loop until the user clicks the close button.
    done = False

    # Used to manage how fast the screen updates
    clock = pygame.time.Clock()

    # -------- Main Program Loop -----------
    while not done:
        # --- Main event loop
        mouse_pos = [0, 0]
        mouse_click = 0
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                done = True
            elif event.type == pygame.MOUSEBUTTONUP:
                mouse_pos = event.pos
                mouse_click = event.button
            elif event.type == VIDEORESIZE:
                window_size = event.dict['size']
                screen = pygame.display.set_mode(event.dict['size'], HWSURFACE | 
    DOUBLEBUF | RESIZABLE)

        # --- Game logic should go here
        if mouse_click == 1:
            for i in xrange(0, 2, 1):
                for a in xrange(0, 2, 1):
                    if a+window_size[0]/3 > mouse_pos[1] > a and 
    i+window_size[1]/3 > mouse_pos[0] > i:
                        table[i][a] = 1
        # --- Screen-clearing code goes here
    
        # Here, we clear the screen to white. Don't put other drawing commands
        # above this, or they will be erased with this command.

        # If you want a background image, replace this clear with blit'ing the
        # background image.
        screen.fill(WHITE)

        # --- Drawing code should go here
        for i in xrange(0, window_size[1], window_size[1]/3):
            for a in xrange(0, window_size[0], window_size[0]/3):
                pygame.draw.rect(screen, BLACK, [a, i, a+window_size[0]/3, 
    i+window_size[1]/3], 5)

                pygame.draw.line(screen, RED, [a, i], [a+window_size[0]/3, 
    i+window_size[1]/3], 5)
                pygame.draw.line(screen, RED, [a+window_size[0]/3, i], [a, 
    i+window_size[1]/3], 5)

                pygame.draw.ellipse(screen, GREEN, [a, i, a+window_size[0]/3, 
    i+window_size[1]/3], 5)
        # --- Go ahead and update the screen with what we've drawn.
            pygame.display.flip()

        # --- Limit to 60 frames per second
        clock.tick(60)

    # Close the window and quit.
    pygame.quit()

for some weird reason, i jast dont get the ellipse right and I dont know why.