Adaptation of the single-square Battleship game from the Codecademy Python course to use the setup/game loop pattern favoured by Al Sweigart in his Python games book. Variable board size introduced too.

Python Simple Battleship

from random import randint

board = []

print ''' 
Welcome to Battleship! First, let's set up the board...
'''
board_size = raw_input("What board size do you want to play?")

board_size = int(board_size)

for x in range(0, board_size):
    board.append(["O"] * board_size)

def random_row(board):
    return randint(0, len(board) - 1)

def random_col(board):
    return randint(0, len(board[0]) - 1)

ship_row = random_row(board)
ship_col = random_col(board)

print '''
Please note: column 1 and row one are represented by 0. 
Good luck, commander!
'''
game_over = False
while game_over == False:    
    def print_board(board):
        for row in board:
            print " ".join(row)
    
    print_board(board)
    
    guess_row = raw_input("Guess Row:")
    guess_col = raw_input("Guess Col:")
    
    if guess_row == '':
        print "Invalid Row."
        guess_row = raw_input("Guess Row:")
    elif guess_col == '':
        print "Invalid Col."
        guess_col = raw_input("Guess Col:")
    
    guess_row = int(guess_row)
    guess_col = int(guess_col)
    
    if guess_row == ship_row and guess_col == ship_col:
        print "Congratulations! You sank my battleship!"
        game_over = True
    else:
        if guess_row > len(board)-1 or guess_col > len(board)-1:
            print "Oops, that's not even in the ocean."
        elif board[guess_row][guess_col] == "X":
            print "You guessed that one already."
        else:
            board[guess_row][guess_col] = "X"
            print "You missed my battleship!"