cannot unpack non-iterable int object в коде, как решить?

Программирую одну игру, но почему-то в коде возникает ошибка:

line 173, in draw_drag
    color, type = selected_piece[0]
    ^^^^^^^^^^^
TypeError: cannot unpack non-iterable int object

Подскажите, как это можно исправить? Вот кусок кода, который может помочь.

 class Sprite(pygame.sprite.Sprite):
    def __init__(self, x, y, filename):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.image.load(filename).convert_alpha()
        self.size = self.image.get_size()
        self.image = pygame.transform.scale(self.image, (int(self.size[0] // 10), int(self.size[1] // 10)))
        self.x = x
        self.y = y
        self.rect = self.image.get_rect(center=(x, y))
        self.image.set_colorkey((255, 255, 255))

    balls = pygame.sprite.Group()
balls.add((Sprite(55, 55, 'c.jpg')), (Sprite(145, 55, 'c3.jpg')), (Sprite(235, 55, 'c.jpg')))


def create_board():
    board = []
    for y in range(8):
        board.append([])
        for x in range(8):
            board[y].append(None)
    for x in range(0, 8):
        board[0][x] = ('black', 'circle')
    for x in range(0, 8):
        board[7][x] = ('white', 'circle')

    return board


def draw_pieces(screen, board, selected_piece):
    sx, sy = None, None
    if selected_piece:
        piece, sx, sy = selected_piece
    for y in range(8):
        for x in range(8):
            piece = board[y][x]
            if piece:
                selected = x == sx and y == sy
                color, type = piece
                for ball in balls:
                    screen.blit(ball.image, ball.rect)
                    balls.update()
            
                pos = pygame.Rect(BOARD_POS[0] + x * TILESIZE + 1, BOARD_POS[1] + y * TILESIZE + 1, TILESIZE, TILESIZE)
               

def draw_selector(screen, piece, x, y):
    if piece != None:
        rect = (BOARD_POS[0] + x * TILESIZE, BOARD_POS[1] + y * TILESIZE, TILESIZE, TILESIZE)
        pygame.draw.rect(screen, (255, 0, 0, 50), rect, 2)


def get_square_under_mouse(board):
    mouse_pos = pygame.Vector2(pygame.mouse.get_pos()) - BOARD_POS
    x, y = [int(v // TILESIZE) for v in mouse_pos]
    try:
        if x >= 0 and y >= 0: return board[y][x], x, y
    except IndexError:
        pass
    return None, None, None


def draw_drag(screen, board, selected_piece):
    if selected_piece:
        piece, x, y = get_square_under_mouse(board)
        if x != None:
            rect = (BOARD_POS[0] + x * TILESIZE, BOARD_POS[1] + y * TILESIZE, TILESIZE, TILESIZE)
            pygame.draw.rect(screen, (0, 255, 0, 50), rect, 2)

        color, type = selected_piece[0]
        for ball in balls:
            screen.blit(ball.image, ball.rect)
            balls.update()
       
        pos = pygame.Vector2(pygame.mouse.get_pos())
        
        balls.update()
        selected_rect = pygame.Rect(BOARD_POS[0] + selected_piece[1] * TILESIZE,
                                    BOARD_POS[1] + selected_piece[2] * TILESIZE, TILESIZE, TILESIZE)
        pygame.draw.line(screen, pygame.Color('red'), selected_rect.center, pos)
        return x, y


def main():
    pygame.init()
    screen = pygame.display.set_mode((800, 800))
    board = create_board()
    board_surf = create_board_surf()
    clock = pygame.time.Clock()
    selected_piece = None
    drop_pos = None
    while True:
        piece, x, y = get_square_under_mouse(board)
        events = pygame.event.get()
        for e in events:
            if e.type == pygame.QUIT:
                return
            if e.type == pygame.MOUSEBUTTONDOWN:
                if piece != None:
                    selected_piece = piece, x, y
            if e.type == pygame.MOUSEBUTTONUP:
                if drop_pos:
                    piece, old_x, old_y = selected_piece
                    board[old_y][old_x] = 0
                    new_x, new_y = drop_pos
                    board[new_y][new_x] = piece
                selected_piece = None
                drop_pos = None

        screen.fill(pygame.Color('black'))
        screen.blit(board_surf, BOARD_POS)
        draw_pieces(screen, board, selected_piece)
        draw_selector(screen, piece, x, y)
        drop_pos = draw_drag(screen, board, selected_piece)

        pygame.display.flip()
        clock.tick(60)


if __name__ == '__main__':
    main()