something with numpy not very interesting

from collections import namedtuple


import numpy as np
# read more about numpy


# sentinel
# read more about the use of it
# https://python-patterns.guide/python/sentinel-object/
EXIT = object()
TERM = object()


def main():
    # main loop
    while True:
        result = menu()
        if result is EXIT:
            # here he exits
            print('Exit!')
            break
        elif result is TERM:
            # same here
            # just to show that you can handle different
            # sentinel objects
            print('TERM!')
            break
        # no exit
        print_result(result)
        # still in loop


def print_result(result):
    print()
    print('=======')
    print('Result:')
    print(result)
    print()


def get_option(last_index):
    while True:
        try:
            option = int(input("Please choose and option: "))
        except ValueError:
            print('Invalid value.')
            continue
        if not (1 <= option <= last_index):
            print('Value is not in menu')
            continue
        return option


def menu():
    """
    This is not the best implementation.
    """
    for index, entry in enumerate(option_mapping, start=1):
        print(f'{index:<2d}. {entry.text}')
    # using index, which is the last value
    # yes, for-loops leaks
    last_index = index
    # hint, Python indicies starts with 0
    option = get_option(last_index) - 1
    # print('Option:', option)
    entry = option_mapping[option]
    if entry.function is EXIT:
        return EXIT
    elif entry.function is TERM:
        return TERM
    return entry.function()


def array_2by2():
    """
    I was too lazy to find a better function
    to create a 2by2 matrix.

    2x2 matricies are used for 2d graphics
    3x3 for 3d
    4x4 for translation matrix in 3d space

    https://en.wikipedia.org/wiki/Rotation_matrix
    """
    # to create an array with zeros with a 2 by 2 shape
    # np.zeros((2, 2))
    # np.ones((2,2))
    return np.arange(1, 5).reshape((2,2))


def square_value():
    # numpy arrays support broadcast multiplication
    # you can do also matrix multiplacation
    # dot product, cross product, etc.
    return array_2by2() ** 2


def add_3():
    """
    Functions should have alsways a doctstring

    Here array_2by2 is called and 3 is added to the result.
    The result returns
    """
    return array_2by2() + 3


def multiply_by5():
    return array_2by2() * 5


# mapping must be defined after the functions has been created
# if you change the order, you get a NameError


menu_entry = namedtuple("Entry", "function text")
option_mapping = (
    menu_entry(array_2by2, "Create a 2-by-2 Array"),
    menu_entry(square_value, "Square Value"),
    menu_entry(add_3, "Add 3 to Elements"),
    menu_entry(multiply_by5, "Multiply Elements"),
    menu_entry(EXIT, "Exit"),
    menu_entry(TERM, "Terminate"),
)


if __name__ == '__main__':
    main()