This is a small python script which can be used to encrypt/decrypt files
pip install pyencrypt
pyencrypt -e random_file.txt
The encryption mode encrypts the file using the given key and creates an encrypted file using the same filename with .pec added to the end. In the above example the filename would be therefore random_file.txt.pec.
pyencrypt -d random_file.txt.pec
The decryption mode decrypts the file and writes creates a decrypted file using the original filename
Pyencrypt uses the AES 256 bit algorithm which is regarded as safe today. Note that pyencrypt does not use any authentication method so it is not safe against modifications.
If the key was forgotten there is no possible way to reconstruct the key either than breaking the AES encryption using brute force mechanisms or other possible ways to break encryptions.