my_list = [[21, 52, 4, 74], [], [7, 8, 4, 1], [], []]

print("列表是：")
print(my_list)

my_result = [row for row in my_list if len(row) > 0]

print("筛选结果为：")
print(my_result)

列表是：
[[21, 52, 4, 74], [], [7, 8, 4, 1], [], []]
筛选结果为：
[[21, 52, 4, 74], [7, 8, 4, 1]]