二维矩阵转置

a=[
[1,2,3],
[4,5,6],
[7,8,9],
[10,11,12]
]
方式1：
result_list = []
for i in range(3):
list_inner = []
#定义一个list存放新二维数组的每行元素，存放原列表的每列元素
for l in a:
list_inner.append(l[i])
result_list.append(list_inner)
print result_list

方式2：一行
print [ [l[i] for l in a] or i in range(3)]

删除二维矩阵的某一列
只保存某些列
s
a=[
[1,2,3],
[4,5,6],
[7,8,9],
[10,11,12]
]

print [ [ l[i] for i in [1,2]] for l in a]