This is the best example of Fernet encryption that I have found.

crypto03.py

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
# crypto03.py - Monday, December 16, 2019
# Ref: https://www.thepythoncode.com/article/encrypt-decrypt-files-symmetric-python
""" This is the best example of Fernet encryption that I have found """
__version__ = '1.0.0'

from datetime import datetime
from shutil import copy2

from cryptography.fernet import Fernet
from tzlocal import get_localzone


def main():
	# generate and write a new key
	# write_key()

	# load the previously generated key
	key = load_key()

	message = "some secret message".encode()
	print("Message to be encrypted: %s" % message)

	# initialize the Fernet class
	f = Fernet(key)

	# encrypt the message
	encrypted = f.encrypt(message)

	# print how it looks
	print(encrypted)

	decrypted_encrypted = f.decrypt(encrypted)
	print(decrypted_encrypted)

	# uncomment this if it's the first time you run the code, to generate the key
	# write_key()

	# load the key
	key = load_key()

	# file name
	file = "data.csv"

	# encrypt it
	encrypt(file, key)

	# copy it
	copy2(file, file + '.encrypted')

	# decrypt the file
	decrypt(file, key)
	return


def write_key():
	"""
	Generates a key and save it into a file
	"""
	key = Fernet.generate_key()
	with open("key.key", "wb") as key_file:
		key_file.write(key)


def load_key():
	"""
	Loads the key from the current directory named `key.key`
	"""
	return open("key.key", "rb").read()


def encrypt(filename, key):
	"""
	Given a filename (str) and key (bytes), it encrypts the file and write it
	"""
	f = Fernet(key)
	with open(filename, "rb") as file:
		# read all file data
		file_data = file.read()

	# encrypt data
	encrypted_data = f.encrypt(file_data)

	# write the encrypted file
	with open(filename, "wb") as file:
		file.write(encrypted_data)
	return


def decrypt(filename, key):
	"""
	Given a filename (str) and key (bytes), it decrypts the file and write it
	"""
	f = Fernet(key)
	with open(filename, "rb") as file:
		# read the encrypted data
		encrypted_data = file.read()
	# decrypt data
	decrypted_data = f.decrypt(encrypted_data)
	# write the original file
	with open(filename, "wb") as file:
		file.write(decrypted_data)
	return

def init():
	print("Run Start: %s" % _run_dt)
	return


def eoj():
	print("Run Stop : %s" % datetime.now(tz).replace(microsecond=0))
	return


def debug_breakpoint():
	pass
	return


if __name__ == '__main__':
	_run_utc = datetime.now()
	tz = get_localzone()
	_run_dt  = _run_utc.astimezone(tz).replace(microsecond=0)
	_fdate = _run_dt.strftime("%Y-%m-%d")

	init()
	main()
	eoj()