After defining print_board(board), isn't board converted into a list? Because when we print board we see no square brackets. Tested the type on an external IDE and it gives me a string.
Which brings me to:
board[int(guess_row)][int(guess_col)] = "X"
How can you subset board with rows and columns if board is a string.
from random import randint board =  for x in range(0, 5): board.append(["O"] * 5) def print_board(board): for row in board: print " ".join(row) print_board(board) def random_row(board): return randint(0, len(board) - 1) def random_col(board): return randint(0, len(board) - 1) ship_row = random_row(board) ship_col = random_col(board) guess_row = int(raw_input("Guess Row:")) guess_col = int(raw_input("Guess Col:")) print ship_row print ship_col # Write your code below! if guess_row == ship_row and guess_col == ship_col: print "Congratulations! You sank my battleship!" else: print "You missed my battleship!" board[int(guess_row)][int(guess_col)] = "X" print print_board(board)