Python NumPy Module Cheatsheet

Import NumPy Module

import numpy as np

NumPy Arrays

Array Definition

my_list = [92, 94, 88, 91, 87] 
numpy_array_from_list = np.array(my_list)

Array from CSV File

csv_file_name = 'test_2.csv'

numpy_array_from_csv_file = np.genfromtxt(csv_file_name, delimiter=',')

Two-Dimensional Array

two_dim_array = np.array([[1, 2, 3, 4, 5],
                          [6, 7, 8, 9, 10],
                          [11, 12, 13, 14, 15]])

The two-dimensional array itself must have outer brackets. Each array must have the same number of elements.

Operations on NumPy Arrays

Adding or Multiplying

numpy_array = np.array([1, 2, 3, 4, 5])
print(numpy_array + 1)
# returns [2, 3, 4, 5, 6]

print(numpy_array ** 2)
# returns [1, 2, 9, 16, 25]

Adding Values from Two Arrays

numpy_array1 = np.array([1, 2, 3, 4, 5])
numpy_array2 = np.array([6, 7, 8, 9, 10])
print(numpy_array1 + numpy_array2)
# returns [7, 9, 11, 13, 15]

Math Functions

Variance

import numpy as np

dividends_microsoft_eur = [0.6358, 0.6308, 0.6364, 0.6854, 0.6876, 0.7016, 0.7016, 0.7906]
variance_dividends_microsoft = np.var(dividends_microsoft_eur)

print('The variance of Microsoft stock dividends in 2023 and 2024 is', variance_dividends_microsoft)