list的append与extend

1.针对一维

append: 列表添加一个元素（直接嵌套一个list）

l1 = [2, 3, 4]
l2 = [7, 8, 9]
l1.append(l2)
l1

[2, 3, 4, [7, 8, 9]]

extend：两个列表合并：

l1 = [2, 3, 4]
l2 = [7, 8, 9]
l1.extend(l2)
l1

[2, 3, 4, 7, 8, 9]

2.针对二维的情况

appen：

l1 = [[2, 3, 4],[2, 3, 4]]
l2 = [[7, 8, 9],[7, 8, 9]]
l1.append(l2)

>>> l1
[[2, 3, 4], [2, 3, 4], [[7, 8, 9], [7, 8, 9]]]

extend：

l1 = [[2, 3, 4],[2, 3, 4]]
l2 = [[7, 8, 9],[7, 8, 9]]
l1.extend(l2)

>>> l1
[[2, 3, 4], [2, 3, 4], [7, 8, 9], [7, 8, 9]]

3.二维形成一个新的list 

extend：

import numpy as np
l=[]
l1 = [[2, 3, 4],[2, 3, 4]]
l2 = [[7, 8, 9],[7, 8, 9]]
l.extend(l1)
l.extend(l2)

>>> l
[[2, 3, 4], [2, 3, 4], [7, 8, 9], [7, 8, 9]]
>>> np.concatenate(l,axis=0)
array([2, 3, 4, 2, 3, 4, 7, 8, 9, 7, 8, 9])

append：

import numpy as np
l=[]
l1 = [[2, 3, 4],[2, 3, 4]]
l2 = [[7, 8, 9],[7, 8, 9]]
l.append(l1)
l.append(l2)

>>> l
[[[2, 3, 4], [2, 3, 4]], [[7, 8, 9], [7, 8, 9]]]
>>> np.concatenate(l,axis=0)
array([[2, 3, 4],
       [2, 3, 4],
       [7, 8, 9],
       [7, 8, 9]])