Place n queens on a nxn chess board, where no queen can attack another

queens.py

# Place n queens on a nxn chess board, where no queen can attack another

def make_board(n):
    return [[0 for i in range(n)] for i in range(n)]


def print_board(board):
    for row in board:
        for col in row:
            print(str(col) + " ", end="")
        print()


def place_queens(board):
    n = len(board)
    cols = [i for i in range(n)]

    def placeable(row, col):
        # check row
        for r in board[row]:
            if r == 1:
                return False
        # check col
        for c in board:
            if c[col] == 1:
                return False
        # check diags
        ## up left
        r, c = row - 1, col - 1
        while r > -1 and c > -1:
            if board[r][c] == 1:
                return False
            else:
                r -= 1
                c -= 1
        ## up right
        r, c = row - 1, col + 1
        while r > -1 and c < n:
            if board[r][c] == 1:
                return False
            else:
                r -= 1
                c += 1
        # valid
        return True

    def drop(l, item):
        new = l.copy()
        new.remove(item)
        return new

    def _place_queens(row, cols):
        if len(cols) == 0:
            print("SOLUTION:")
            print_board(board)
            exit(0)  # remove to find ALL solutions
        else:
            for col in cols:
                if placeable(row, col):
                    # choose
                    board[row][col] = 1
                    # explore
                    _place_queens(row + 1, drop(cols, col))
                    # unchoose
                    board[row][col] = 0

    _place_queens(0, cols)


if __name__ == '__main__':
    board = make_board(8)
    place_queens(board)

SOLUTION:
1 0 0 0 0 0 0 0
0 0 0 0 1 0 0 0
0 0 0 0 0 0 0 1
0 0 0 0 0 1 0 0
0 0 1 0 0 0 0 0
0 0 0 0 0 0 1 0
0 1 0 0 0 0 0 0
0 0 0 1 0 0 0 0