board = [[] for i in range(3)]
for i in board:
for j in range(3):
i.append(' ')
for i in board:print(i)
'''
['', '', '']
['', '', '']
['', '', '']'''
print(i for i in board) #<generator object <genexpr> at 0x0000026E45CB69E8>
为什么最后两行打印两种不同的东西？