Code

    engine = create_engine('sqlite:///login.db', connect_args={'check_same_thread': False}, echo=True)
    app = Flask(__name__)
    app.secret_key = os.urandom(12)

    def do_login(self):

            POST_USERNAME = str(request.form['username'])
            POST_PASSWORD = str(request.form['password'])

            Session = sessionmaker(bind=engine)
            s = Session()
            query = s.query(User).filter(User.username.in_([POST_USERNAME]), User.password.in_([POST_PASSWORD]) )
            result = query.first()
            if result:
                session['logged_in'] = True
            else:
                flash('Password Errada!')
            return render_template('login.html')