Python-zip 函数

矩阵运算里面用到的比较多
用法:

zip([iterable, ...])

将可迭代对象中的元素依次打包,组成一个个的元组,然后返回这些元组组成的可迭代对象.若有长度不等的几个参数,按元素最少的为准

list1 = [1, 2, 3]
list2 = [4, 5, 6]
list3 = [7, 8, 9]
x = zip(list1, list2, list3)
print(x)
print(list(x))

#输出
<zip object at 0x10f35d808>
[(1, 4, 7), (2, 5, 8), (3, 6, 9)]

注意返回的是一个zip迭代器.

a = [[1,2,3],[4,5,6],[7,8,9]]
for i in a:
    print(i)

b = zip(*a)
print(b)
for i in b:
    print(list(i))

c = [[j[i] for j in a] for i in range(len(a[0]))]
for i in c:
    print(i)

#输出
[1, 2, 3]
[4, 5, 6]
[7, 8, 9]
<zip object at 0x10dd26988>
[1, 4, 7]
[2, 5, 8]
[3, 6, 9]
[1, 4, 7]
[2, 5, 8]
[3, 6, 9]

这里zip(*a)相当于解压.
如果将二维列表a看作一个3*3的矩阵,则这里实现了矩阵的转置.

另外如果zip函数里面的参数指向同一个iterable:

a = [1, 2, 3, 4, 5, 6]
b = zip(*([iter(a)]*3))
for i in b:
    print(i)
#输出
(1, 2, 3)
(4, 5, 6)

a = [1, 2, 3, 4, 5, 6]
for j in ([iter(a)]*2):
    for k in j:
        print(k)
#输出
1
2
3
4
5
6