.join() function not working in Python

Question

I was wondering if someone could help me figure out why my few lines of code isn't working in Python. I am trying to create my own version of the Battleship game, but I can't seem to get the .join() function to work.

Here is my code:

board = []

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

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

print_board(board)

However, my output ends up being:

OOOOO
OOOOO
OOOOO
OOOOO
OOOOO

when I feel like it should be:

O O O O O
O O O O O
O O O O O
O O O O O
O O O O O

Any help is appreciated! Thank you!

Answer 1

Your problem is here:

board.append(["O" *5 ])

Doing "O" * 5 doesn't create a list of strings. It simply creates a single string:

>>> "O"*5
'OOOOO'
>>> 

Thus, what you basically doing when using str.join is:

>>> ' '.join(['OOOOO'])
'OOOOO'
>>> 

This of course, fails, since the list passed into str.join has a single element, and str.join works by concatenating a list with multiple elements. From the documentation for str.join:

str.join(iterable)

Return a string which is the concatenation of the strings in iterable. A TypeError will be raised if there are any non-string values in iterable, including bytes objects. The separator between elements is the string providing this method.

What you need to do instead is create each row in your board with five 'O's:

board = [["O"] * 5 for _ in range(5)]