"TypeError: Object of type bytes is not JSON serializable"

Question

Trying to dump a dictionary in a JSON file gives me the error "TypeError: a bytes-like object is required, not 'str'"

I already tried to remove the bytes conversion part of the "encrypt_string" function but it gives me the error "TypeError: a bytes-like object is required, not 'str'"

#!/usr/bin/python3

# Imports
import json
import base64
from cryptography.fernet import Fernet

# Save
def encrypt_string(string, f):
    return str(f.encrypt(base64.b64encode(bytes(string,'utf-8'))).decode('utf-8'))

def encrypt_dict(dict):
    fk = Fernet.generate_key().decode('utf-8')
    f = Fernet(fk)
    ed = {}
    ed['fk'] = base64.b64encode(bytes(fk, 'utf-8'))
    for key, value in dict.items():
        ekey = encrypt_string(key, f)
        evalue = encrypt_string(value, f)
        ed[ekey[::-1]] = evalue[::-1]
    return ed

def save_game(slot, savename):
    print("Saving file...")
    path = 'saves/savegame{0}.json'.format(slot)
    data = {
        'game': 'Game name here',
        'version': 'Version here',
        'author': 'Author here',
        'savename': str(savename),
    }
    data = encrypt_dict(data)
    with open(path, 'w') as f:
        json.dump(data, f)
        f.close()
    print('Data saved in', path)

# Main
import gamemodule as gm

def main():
    print("Running...")
    gm.save_game(1, 'test')
    input("Press any button to continue...")

I expected the file the program to save the game data but it just returns the "TypeError: a bytes-like object is required, not 'str'" error

I think that it's related to me encoding the variables in the encrypt_dict function but I'm not sure, I've browsed other problems similar to this one but I didn't find anything that fixed my error

Solution

The problem is that base64.b64encode(bytes(fk, 'utf-8')) in encrypt_dict returns a byte-string (b'NGtUbnNEc2hXZTlsOE1tcWVoVkNOUjMtWVIxcVZrWGV1WlBVcjJ2WkhHST0=') while encrypt_string returns a normal string (no leading b). The JSON format only supports unicode strings.

This can be fixed by replacing line 16 in encrypt_dict with

ed['fk'] = base64.b64encode(bytes(fk, 'utf-8')).decode("ascii")