N-Queens: backtrack to print all solutions

nqueens.py

def isSafe(board, row, col):

    for i in range(col):
        if board[row][i] == 'Q':
            return False

    i = row
    j = col
    while i >= 0 and j >= 0:
        if board[i][j] == 'Q':
            return False
        i -= 1
        j -= 1

    i = row
    j = col
    while j >= 0 and i < len(board):
        if board[i][j] == 'Q':
            return False
        i = i + 1
        j = j - 1

    return True


def solveNQUtil(board, col):

    if col == len(board):
        solution = [''.join(row) for row in board]
        yield solution

    for i in range(len(board)):
        if (isSafe(board, i, col)):
            board[i][col] = 'Q'
            yield from solveNQUtil(board, col + 1)
            board[i][col] = '.'


def solveNQ():

    board = [['.' for j in range(8)]
             for i in range(8)]

    return solveNQUtil(board, 0)


for solution in solveNQ():
    print(solution)