[Tutor] Help writing a function

[Grace Sanford]

I need suggestions/help for writing the following 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.
    """