[Tutor] Help finishing a function

[Grace Sanford]

I am wondering if someone can help/advise me on finishing the code for this
function:

import turtle
import time
import random

# This list represents the board. It's a list
# of nine strings, each of which is either
# "X", "O", "_", representing, respectively,
# a position occupied by an X, by an O, and
# an unoccupied position. The first three
# elements in the list represent the first row,
# and so on. Initially, all positions are
# unoccupied.
the_board = [ "_", "_", "_",
              "_", "_", "_",
              "_", "_", "_"]

def do_user_move(board, x, y):
    """
    signature: list(str), int, int -> bool
    Given a list representing the state of the board
    and an x,y screen coordinate pair indicating where
    the user clicked, update the board
    with an O in the corresponding position.
    The function returns a bool indicated if
    the operation was successful: if the user
    clicks on a position that is already occupied
    or outside of the board area, the move is
    invalid, and the function should return False,
    otherise True.
    """
    print("user clicked at "+str(x)+","+str(y))
    width = turtle.window_width ()
    height = turtle.window_height ()
    #Given coordinates of user click, update board with "O" in
corresponding position
    if x<(-width/2)+(width/3):
        column = 0
    elif x>(-width/2)+(width/3) and x<(width/2)-(width/3):
        column = 1
    elif x>(width/2)-(width/3):
        column = 2
    if y>(height/2)-(height/3):
        row = 0
    elif y<(height/2)-(height/3) and y>(-height/2)+(height/3):
        row = 1
    elif y<(-height/2)+(height/3):
        row = 2
    p = row * 3 + column
    for board[p]=="_":
    pass #code here
    #Check if user clicks on a position that is already occupied
    pass #code here
    #Check if user clicks outside the board area
    if x<(-width/2) or x>(width/2) or y<(-height/2) or y>(height/2):
        return False