How to use append in python

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append() function

Description: Add an element object at the end (end) of the list ls

Syntax: ls.append(object) -> None No return value

Example:

a=[1,2,3]
a.append(5)

At this time, the running result is [1, 2, 3, 5]

a=[1,2,3]
a.append([5])

At this time, running The result is [1, 2, 3, [5]]

The result is no longer an array, but a list

Use append to generate a multi-dimensional array:

import numpy as np
a=[] 
for i in range(5): 
    a.append([])
    for j in range(5): 
        a[i].append(i)

The results are as follows:

[[0, 0, 0, 0, 0],
 [1, 1, 1, 1, 1],
 [2, 2, 2, 2, 2],
 [3, 3, 3, 3, 3],
 [4, 4, 4, 4, 4]]

Matrix transpose function transpose method:

a=np.transpose(a)

The results are as follows:

  ([[0, 1, 2, 3, 4],
       [0, 1, 2, 3, 4],
       [0, 1, 2, 3, 4],
       [0, 1, 2, 3, 4],
       [0, 1, 2, 3, 4]])

Array merge operation :

h=np.arange(-2,2,1)
h.shape
k1=np.c_[h,h] #横向合并函数1 np.c_，将数组转化为列向量
k2=np.hstack((h,h)) #横向合并函数2 np.hstack，将数组作为横向量
print("k1="+str(k1))
print("k2="+str(k2))
l1=np.r_[[h],[h]] #纵向合并函数np.r_
l2=np.vstack((h,h)) #纵向合并函数np.vstack
print("l1="+str(l1))
print("l2="+str(l2))

The results are as follows:

k1=[[-2 -2]
 [-1 -1]
 [ 0  0]
 [ 1  1]]
k2=[-2 -1  0  1 -2 -1  0  1]
l1=[[-2 -1  0  1]
 [-2 -1  0  1]]
l2=[[-2 -1  0  1]
 [-2 -1  0  1]]

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