Python: floodfill algorithm for minesweeper

Question

I'm writing a minesweeper game in python, and am currently trying to implement a floodfill algorithm. This is what I've written:

def floodfill(CURRENT_BOARD, row, col):
count = count_mines(row, col)
if count in POSSIBLE_MINE_NUMBERS:
    CURRENT_BOARD[row][col] = str(count) + ' '
else:
    if CURRENT_BOARD[row][col] == 'P  ':
        CURRENT_BOARD[row][col] = 'P  '
        if row > 0:
            floodfill(CURRENT_BOARD, row - 1, col)
        if row < len(BOARD[row]) - 1:
            floodfill(CURRENT_BOARD, row + 1, col)
        if col > 0:
            floodfill(CURRENT_BOARD, row, col - 1)
        if col < len(BOARD) - 1:
            floodfill(CURRENT_BOARD, row, col + 1)
    else:
        CURRENT_BOARD[row][col] = '  '
        if row > 0:
            floodfill(CURRENT_BOARD, row - 1, col)
        if row < len(BOARD[row]) - 1:
            floodfill(CURRENT_BOARD, row + 1, col)
        if col > 0:
            floodfill(CURRENT_BOARD, row, col - 1)
        if col < len(BOARD) - 1:
            floodfill(CURRENT_BOARD, row, col + 1)

things to note:

POSSIBLE_MINE_NUMBERS = [1,2,3,4,5,6,7,8]

count_mines is a function that counts the number of mines in the surrounding 8 squares of row, col.

the board (CURRENT_BOARD) is a list of lists.

'P ' represents a flag, the algorithm is supposed to skip over flags.

' ' represents an empty space in the board.

The problem is when it is called, I get heaps of errors before it overflows the call stack, and I'm wondering what I've done wrong.

Answer 1

The following jumps out at me:

if CURRENT_BOARD[row][col] == 'P  ':
    CURRENT_BOARD[row][col] = 'P  '
    ...

Here, you are recursing without modifying the board. This could well be the cause of the infinite recursion you're seeing.