18/19 error while not entering a number


#1



https://www.codecademy.com/en/courses/python-beginner-en-4XuFm/2/4?curriculum_id=4f89dab3d788890003000096


How can I make my code not returning an error while i enter anything other than a number when requested?

For now I'm getting this error message when I do it:

Traceback (most recent call last):
File "python", line 28, in
ValueError: invalid literal for int() with base 10: ''


I'd really like to fix this problem so my code doesn't return errors even when I intentionally put letters or other signs.


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)
print ship_row
print ship_col

for turn in range(4):
    guess_row = int(raw_input("Guess Row:"))
    guess_col = int(raw_input("Guess Col:"))
    
    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

you could do the following:

while True:
    try:
         guess_row = int(raw_input("Guess Row:"))
         guess_col = int(raw_input("Guess Col:"))
    except ValueError:
         print "not valid, try again"
    else:
         break

i normally don't give away code like this, but this involved code which is not yet taught. Try except allows us to catch errors and handle them in a custom way


#3

Thank you! Now it works like a charm :slight_smile: Here's my improved code:

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)
print ship_row
print ship_col

for turn in range(4):
    while True:
        try:
             guess_row = int(raw_input("Guess Row:"))
             guess_col = int(raw_input("Guess Col:"))
        except ValueError:
             print "You must enter a number between 0 and 4, try again!"
        else:
             break
    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"

#4

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