login sqlachemy

from flask import Flask, request,render_template,url_for
from flask_sqlalchemy import SQLAlchemy
from flask_login import UserMixin
from sqlalchemy import create_engine



import psycopg2
try:
   conn = psycopg2.connect(host="localhost",
                            user="postgres",
                            password="haslo",
                            database="Wypozyczalnia samochodow")
except:
    print("Show error")
mycursor =conn.cursor()

engine = create_engine('postgresql+psycopg2://postgres:haslo@localhost/Wypozyczalnia samochodow')

app = Flask(__name__)
db = SQLAlchemy(app)
app.config['SQLALCHEMY_DATABASE_URI'] = 'postgresql://postgres:haslo@localhost/Wypozyczalnia samochodow'
app.config['SECRET_KEY'] ='sekretnyklucz'

class User(db.Model,UserMixin):
    _tablename_ = 'uzytkownicy'
    id = db.Column(db.Integer,primary_key=True)
    username = db.Column(db.String(20),unique=True,nullable=False)
    password = db.Column(db.String(80),nullable=False)