Write a program to find the count of numbered cells, given a valid initial board configuration. Below figure is the sample valid initial configuration. code example

Example: preventing players from changing existing entries in tic tac toe game

# Checking whether the position on the tic tac board is occupied or not.
def place_marker(board, marker, position):
    if board[position] == ' ':
        board[position] = marker
    else:
        print("That space is already occupied.")