Encrypting data into Postgres and decrypting from Postgres using sqlalchemy and ORM

I want to encrypt data into Postgres and then decrypt and read from it. I prefer using sqlalchemy and ORM but if it is difficult to do using sqlalchemy and ORM then I am curious to know the other ways also

I tried using the below code, It is encrypting into the database but it is not asking me for any key or anything for the decryption. May I know why?

import sqlalchemy as sa
from sqlalchemy import create_engine
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import sessionmaker

from sqlalchemy_utils import EncryptedType
from sqlalchemy_utils.types.encrypted.encrypted_type import AesEngine

secret_key = 'secretkey1234'
connection_string = '***********'
engine = create_engine(connection_string)
connection = engine.connect()
sa.orm.configure_mappers()
Session = sessionmaker(bind=connection)
session = Session()
Base = declarative_base()
class User(Base):
    __tablename__ = "user"
    id = sa.Column(sa.Integer, primary_key=True)
    username = sa.Column(EncryptedType(sa.Unicode,secret_key,AesEngine,'pkcs5'))
    number_of_accounts = sa.Column(EncryptedType(sa.Integer,secret_key,AesEngine,'oneandzeroes'))
Base.metadata.create_all(connection)

I run the below code for the decryption:

user_id = user.id
session.expunge_all()
user_instance = session.query(User).get(user_id)
print('username: {}'.format(user_instance.username))