一行循环内的错误“'int'对象不可迭代”

Question

为什么这一行会出现错误，当这些都没有返回数字时，“int”类与什么有关系？

choice([cell for cell in row for row in self.rows if not cell.is_num and not cell.is_bomb]).open_cell()

Traceback (most recent call last):
  File "E:\Programming\Python\QT\Mineswiper\minesweeper v2.py", line 148, in <module>
    window = MainWindow()
  File "E:\Programming\Python\QT\Mineswiper\minesweeper v2.py", line 144, in __init__
    choice([cell for cell in row for row in self.rows if not cell.is_num and not cell.is_bomb]).open_cell()
TypeError: 'int' object is not iterable