Decryption of a file using fernet module in python

Question

 def encrypt(self):
        if not os.path.exists(self.filename):
            raise Exception('File does not exist!')

        # Generate a random salt
        salt = Fernet.generate_key()

        # Calculate the HMAC of the salt using the key
        hmac_digest = hmac.new(self.key, salt, hashlib.sha256).digest()

        # Encrypt the data with the salt and key
        fernet = Fernet(salt + self.key)
        with open(self.filename, 'rb') as file:
            file_data = file.read()
        encrypted_data = fernet.encrypt(file_data)

        # Write the encrypted data to the file
        with open(self.filename, 'wb') as file:
            file.write(encrypted_data)

     

 def decrypt(self):
        if not os.path.exists(self.filename):
            raise Exception('File does not exist!')

        # Read the salt and HMAC digest from the separate file
        with open(self.filename + '.salt', 'rb') as file:
                k_sz = Fernet.key_size
                salt = file.read(k_sz)
                hmac_digest = file.read(hashlib.sha256().digest_size)

here in the decrypt function i am trying to get the salt and hmac value stored in the encrypted file. But receiving the error

 File "C:\python programs\test2.py", line 61, in decrypt
    k_sz = Fernet.key_size
           ^^^^^^^^^^^^^^^
AttributeError: type object 'Fernet' has no attribute 'key_size'

i have tried .KEY_SIZE and Fernet(key=None).key_size then it says key value as none not expected