python 创建二维列表，将需要的参数写入 cols 和 rows 即可
list_2d =[[0for col in range(cols)]for row in range(rows)]
实例：
>>> list_2d =[[0for i in range(5)]for i in range(5)]
>>> list_2d[0].append(3)
>>> list_2d[0].append(5)
>>> list_2d[2].append(7)
>>> list_2d
[[0,0,0,0,0,3,5],[0,0,0,0,0],[0,0,0,0,0,7],[0,0,0,0,0],[0,0,0,0,0]]
