Python 3.7.5 : Testing cryptography python package - part 001.

There are many python packets that present themselves as useful encryption and decryption solutions. I recommend before you test them, use them and spend time with them to focus on the correct study of cryptology because many disadvantages and problems can arise in the correct and safe writing of the source code.
Today I will show you a simple example with cryptography python package.
Let's install this with pip3 tool:

[mythcat@desk projects]$ pip3 install cryptography --user

You can read more about this python package on the documentation website.
Let's try a simple method of encryption and decryption.
I will show you how to solve this issue with the class cryptography.hazmat.primitives.ciphers.aead.AESGCM:
The AES-GCM construction is composed of the AES block cipher utilizing Galois Counter Mode (GCM).
The GCM (Galois Counter Mode) is a mode of operation for block ciphers.
An AEAD (authenticated encryption with additional data) mode is a type
of block cipher mode that simultaneously encrypts the message as well as authenticating it.
The Value of AESGCM key must be 128, 192, or 256 bits, see the size of the key:

[mythcat@desk projects]$ python3
Python 3.7.5 (default, Dec 15 2019, 17:54:26) 
[GCC 9.2.1 20190827 (Red Hat 9.2.1-1)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import os
>>> from cryptography.hazmat.primitives.ciphers.aead import AESGCM
>>> aad = None
>>> key = 'catafestcatafestcatafestcatafest'
>>> aesgcm = AESGCM(key.encode('utf-8'))
>>> nonce = '12345678'
>>> data_binary = b'Hello world!'
>>> 
>>> cipher_text = aesgcm.encrypt(nonce.encode('utf-8'), data_binary, aad)
>>> print(cipher_text)
b'0\xab\xd2!mXe\xc3/\xdb\x15\xcaoT\x0f\x1d\xbb&\xc4\x92\xdf\\ZTMD\xa2\x9f'
>>> data_text = aesgcm.decrypt(nonce.encode('utf-8'), cipher_text, aad)
>>> print(data_text)
b'Hello world!'