python: how to replace strings in a nested list of strings

Question

I'm trying to replace strings in a nested list.

board = [
['O', 'X', '.'],
['.', 'O', 'X'],
['.', 'O', 'X']
]

this should end up like

board = [
['O', '*', '.'],
['.', 'O', '*'],
['.', 'O', '*']
]

this is what ive tried:

    new_board = [[x.replace('X', '*') for x in l] for l in board]

it works like this as a single assingment like this but when i try do it in a function it doesnt work. The function must modify the given board in place; it returns None.

def change_player_char(board, player, new_char):

    board = [[new_char if j == player else j for j in i] for i in board]

I call it like:

board = [
['O', 'X', '.'],
['.', 'O', 'X'],
['.', 'O', 'X']
]

change_player_char(board, 'X', '*')
for row in board:
    print(row)

Not sure what doesn't work, but running your code gives [['O', '*', '.'], ['.', 'O', '*'], ['.', 'O', '*']] which appears to be what you want? — bgse
– bgse, Commented Nov 12, 2017 at 3:59
So it turns out it works if I have it out of a function but when i try use it in a function it doesn't work, Updated OP. — Jay Dilla
– Jay Dilla, Commented Nov 12, 2017 at 4:06
You need to call it like this: board = change_player_char(board, 'X', '*') — bgse
– bgse, Commented Nov 12, 2017 at 4:07
The function must modify the given board in place; it returns None. — Jay Dilla
– Jay Dilla, Commented Nov 12, 2017 at 4:11

Transhuman · Accepted Answer · 2017-11-12 03:58:14Z

2

[['*' if j=='X' else j for j in i] for i in board]
#[['O', '*', '.'], ['.', 'O', '*'], ['.', 'O', '*']]

answered Nov 12, 2017 at 3:58

Transhuman

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Ajax1234 · Accepted Answer · 2017-11-12 04:00:05Z

1

You can use map:

board = [
 ['O', 'X', '.'],
 ['.', 'O', 'X'],
 ['.', 'O', 'X']
]
new_board = [list(map(lambda x:"*" if x == "X" else x, i)) for i in board]

Output:

[['O', '*', '.'], 
 ['.', 'O', '*'], 
 ['.', 'O', '*']]

answered Nov 12, 2017 at 4:00

Ajax1234

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