why is the output the same in both elements when i initialize path=“” and does not initialize path with any value

Question

row = [ -1, 0, 1,  0]
col = [  0, 1, 0, -1]

def isSafe(x, y, processed):
    return (0 <= x < M) and (0 <= y < N) and not processed[x][y]

def dfs(board, wo