I am developing a Flask application. It is still relatively small. I had only one app.py file, but because I needed to do database migrations, I divided it into 3 using this guide:

https://realpython.com/blog/python/flask-by-example-part-2-postgres-sqlalchemy-and-alembic/

However, I now can't run my application as there is a circular dependency between app and models.

app.py:

from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from flask import render_template, request, redirect, url_for
import osapp = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = os.environ['DB_URL']
app.config['SQLALCHEMY_TRACK_MODIFICATIONS'] = Falseapp.debug = Truedb = SQLAlchemy(app)from models import User... routes ...    if __name__ == "__main__":app.run()

models.py:

from app import db
class User(db.Model):id = db.Column(db.Integer, primary_key=True)username = db.Column(db.String(80), unique=True)email = db.Column(db.String(120), unique=True)def __init__(self, username, email):self.username = usernameself.email = emaildef __repr__(self):return self.username

manage.py:

from flask_script import Manager
from flask_migrate import Migrate, MigrateCommand
from app import app, dbmigrate = Migrate(app, db)
manager = Manager(app)manager.add_command('db', MigrateCommand)if __name__ == "__main__":manager.run()

They are all in the same directory. When I try to run python app.py to start the server, I receive an error which definitely shows a circular dependency (which is pretty obvious). Did I make any mistakes when following the guide or is the guide wrong? How can I refactor this to be correct?

Thanks a lot.

EDIT: Traceback

Traceback (most recent call last):File "app.py", line 14, in <module>from models import UserFile "/../models.py", line 1, in <module>from app import dbFile "/../app.py", line 14, in <module>from models import User
ImportError: cannot import name User

I propose the following structure:

# app/extensions.py
from flask_sqlalchemy import SQLAlchemy
db = SQLAlchemy()
...# app/app.py
from app.extensions import dbdef create_app(config_object=ProdConfig):app = Flask(__name__.split('.')[0])app.config.from_object(config_object)register_extensions(app)...def register_extensions(app):db.init_app(app)...# manage.py
from yourapp.app import create_app
app = create_app()
app.debug = True
...

In this case, database, app, and your models are all in separate modules and there are no conflicting or circular imports.