How do I correct a circular import with Flask and SQLAlchemy?

I'm working on a flask application that uses SQLAlchemy, and I have the models for the database declared in a different file 'db_schema.py' from the main application file 'app.py'. I am getting a circular import error when trying to import the models from db_schema.py back in to app.py.

Error:

ImportError: cannot import name 'User' from partially initialized module 'db_schema' (most likely due to a circular import) (/home/deric/projects/python/flask/chatroom/chatroom/project/db_schema.py)

db_schema.py

from app import db
from flask_login import UserMixin
from datetime import datetime

class User(db.Model, UserMixin):
    id = db.Column(db.Integer, primary_key = True)
    username = db.Column(db.String(25), unique = True, index = True, nullable = False)
    password = db.Column(db.String(125), unique = False, index = False, nullable = False)
    email = db.Column(db.String(30), unique = True, index = True, nullable = False)
    chatroom_id = db.Column(db.Integer, db.ForeignKey('chatroom.id'))
    messages_sent = db.relationship('Message', backref='sender', lazy='dynamic', cascade='all, delete')


class Chatroom(db.Model):
    id = db.Column(db.Integer, primary_key = True)
    

class Message(db.Model):
    id = db.Column(db.Integer, primary_key = True)
    chatroom_id = db.Column(db.Integer, db.ForeignKey('chatroom.id'))
    sender_id = db.Column(db.Integer, db.ForeignKey('user.id'))
    content = db.Column(db.String(150), unique = False, index = True)
    time_sent = db.Column(db.DateTime, unique = False, index = True, default=datetime.utcnow)

app.py

from flask import Flask, render_template, url_for, redirect, request
from flask_login import LoginManager
from flask_sqlalchemy import SQLAlchemy
from forms import Registration_Form


app = Flask(__name__)
app.config['SQLALCHEMY_DATABASE_URI'] = 'sqlite:///sqlite3.db'
login_manager = LoginManager()
db = SQLAlchemy(app)

from db_schema import User, Message, Chatroom

@login_manager.user_loader
def load_user(user_id):
    return User.query.filter(id=user_id).first()

@app.route('/')
def index():
    return render_template('index.html')

if __name__ == '__main__':
    app.run()

source https://stackoverflow.com/questions/73007688/how-do-i-correct-a-circular-import-with-flask-and-sqlalchemy