Meaning of this error?


#1

Traceback (most recent call last):
File "python", line 30, in
ValueError: invalid literal for int() with base 10: ''


from random import randint

board = []

for x in range(5):
    board.append(["O"] * 5)

def print_board(board):
    for row in board:
        print " ".join(row)

print "Let's play Battleship!"
print_board(board)

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)


# Everything from here on should go in your for loop!
# Be sure to indent four spaces!
for turn in range(4):

    guess_row = int(raw_input("Guess Row:"))
    guess_col = int(raw_input("Guess Col:")) # <- Here is the line 30
    
    if guess_row == ship_row and guess_col == ship_col:
        print "Congratulations! You sunk my battleship!"
        break 
    else:
        if (guess_row < 0 or guess_row > 4) or (guess_col < 0 or guess_col > 4):
            print "Oops, that's not even in the ocean."
        elif (board[guess_row][guess_col] == "X"):
            print "You guessed that one already."
        else:
            print "You missed my battleship!"
            board[guess_row][guess_col] = "X"
        print "Turn", turn + 1
        print_board(board)
    if turn == 3:
                print "Game Over"

#2

Really late reply, I was just scrolling way down..

Anyway - the string '' is not a valid integer, as you can see when you look at it, it's not a number. So when you try to convert it to int, int(''), what is Python supposed to do? Probably not a good idea to return some arbitrary integer, that would be misleading, instead it tells you that you passed an argument that isn't a valid integer literal. So that you can either handle the error after it occurred, or change the code so that you aren't asking Python to convert something that is not a number, into a number.