TypeError: a bytes-like object is required, not 'Key_Private' как решить ошибкy?

#!/usr/bin/env python
# -*- coding: utf-8 -*-
import random
import binascii
import rsa.randnum
import cryptography
from Crypto.Cipher import Salsa20
from cryptography.fernet import Fernet, MultiFernet
import base64
import qrcode
import image
from cryptography.hazmat.backends import default_backend
from cryptography.hazmat.primitives import serialization
from cryptography.hazmat.primitives.asymmetric import rsa, padding
from cryptography.hazmat.backends import default_backend
from authlib.specs.rfc7519 import jwt
from cryptography.hazmat.primitives.serialization import load_pem_public_key
from cryptography import x509
from cryptography.hazmat.primitives.hashes import HashContext

private_key = rsa.generate_private_key(
    public_exponent=65537,
    key_size=2048,
    backend=default_backend()
    )

pem = private_key.private_bytes(
    encoding=serialization.Encoding.PEM,
    format=serialization.PrivateFormat.PKCS8,
    encryption_algorithm=serialization.BestAvailableEncryption(b'mypassword')
    )
pem.splitlines()[0]

class Key_Private():

    def __init__(self, private_key):
        self.__private_key = private_key

    def private_key_funct(self):
        return self.__private_key

    def __str__(self):
        return 'Your private key: {0}'.format(self.__private_key)

new_private_key = Key_Private(private_key)

file_1 = open("PrivateKey.pem", "wb")
file_1.write(new_private_key)
file_1.close()

Ошибка TypeError: a bytes-like object is required, not 'Key_Private'