NumPy

pip install numpy 

Once installed, import the library with the alias np

import numpy as np 

Converting list into numpy array

a = [2,4,6,8] 
print(np.array(a)) 

One dimensional array

a1 = np.array([1, 2, 3]) 
print(a1) 

# output 
[1 2 3] 

Two dimensional array

a2 = np.array([[1, 2], [3, 4]]) 
print(a2) 

# output 
[[1 2] 
 [3 4]] 

Three dimensional array

a3 = np.array([[[1, 2], [3, 4]],    # 3D array 
               [[5, 6], [7, 8]]]) 
print(a3) 

# output 
[[[1 2] 
  [3 4]] 

 [[5 6] 
  [7 8]]] 

Create an array filled with zeros

a0 = np.zeros((3, 3)) 
print(a0) 

# output 
[[0. 0. 0.] 
 [0. 0. 0.] 
 [0. 0. 0.]] 

Create an array filled with ones

a1  = np.ones((2, 2)) 
print(a1) 

# output 
[[1. 1.] 
 [1. 1.]] 

Create an array filled with a range

ar  = np.arange(0, 10, 2) 
print(ar) 

# output 
[0 2 4 6 8] 

single element

a1 = np.array([10, 20, 30, 40, 50]) 
print(a1[2])             #= 30 

last element

a2 = np.array([10, 20, 30, 40, 50]) 
print(a2[-1])            #= 50 

row 1, column 0

a2 = np.array([[1, 2, 3], 
               [4, 5, 6], 
               [7, 8, 9]]) 
print(a2[1, 0])          #= 4 

Array Slicing
row slice

a = np.array([[1, 2, 3], 
              [4, 5, 6]]) 
print(a[1:4])            #= [[4 5 6]] 

all rows, column 1

a = np.array([[1, 2, 3], 
              [4, 5, 6]]) 
print(a[:, 1])           #= [2 5] 

Basic Arithmetic Operations

x = np.array([1, 2, 3]) 
y = np.array([4, 5, 6]) 

print(x + y)             #= [5 7 9] 
print(x - y)             #= [-3 -3 -3] 
print(x * y)             #= [ 4 10 18] 
print(x / y)             #= [0.25 0.4  0.5 ] 

Resizing arrays - numpy.resize

import numpy as np 
arr = np.array([1, 2, 3, 4, 5, 6]) 
arr.resize((2, 3)) 
print(arr) 

# output 
[[1 2 3] 
 [4 5 6]] 

arr = np.array([1, 2, 3, 4, 5, 6]) 
arr.resize((3, 4)) 
print(arr) 

# output 
[[1 2 3 4] 
 [5 6 0 0] 
 [0 0 0 0]] 

arr = np.array([10, 20, 30, 40, 50]) 
arr.resize((2, 2)) 
print(arr) 

# output 
[[10 20] 
 [30 40]]