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Flask. Could not build url for endpoint 'index'

Please help in solving this problem.
I have a project in Flask with a structure:
project
- main.py
- app
-- __init__.py
-- main
--- __init__.py
--- routes.py
-- auth
--- __init__.py
--- routes.py
--- forms.py
-- templates
--- index.html
app/main/routes.py
from flask import render_template
from app.main import bp
#bp.route('/')
def index():
return render_template('index.html')
app/main/init.py
from flask import Blueprint
bp = Blueprint('main', __name__)
from app.main import routes
app/init.py
from flask import Flask
from config import Config
def create_app(config_class=Config):
app = Flask(__name__)
app.config.from_object(Config)
from app.auth import bp as auth_bp
app.register_blueprint(auth_bp, url_prefix='/auth')
from app.main import bp as main_bp
app.register_blueprint(main_bp)
return app
main.py
from app import create_app
app = create_app()
if __name__ == '__main__':
app.run()
I get an error when I start the application:
Could not build url for endpoint 'index'. Did you mean 'main.index' instead?
Tried to insert main.index. instead of index.html in combination with template_folder='../templates'. But then it doesn't find the template.

Flask - Can't import app inside test file

I'm trying to write some unit tests for a flask application I made. The project is setup like this:
apiproject (parent folder containing everything)
/venv
run.py
requirements.txt
/project
__init__.py
/departments
__init__.py
routes.py
models.py
/users
__init__.py
routes.py
models.py
/tests
TestUsers.py
run.py:
from project import app
if __name__ == '__main__':
app.run(debug=True)
my actual app is created under project/init.py
from flask import Flask, jsonify, Response
from flask_sqlalchemy import SQLAlchemy
from flask_marshmallow import Marshmallow
import os
from dotenv import load_dotenv
from flask_cors import CORS
load_dotenv(verbose=False)
DB_URL = os.getenv("DATABASE_URL")
# initialize the application
app = Flask(__name__)
and in my TestUsers.py I have this:
import json
from project import app
import unittest
from dotenv import load_dotenv
load_env(verbose=False)
class TestUsers(unittest.TestCase):
def setUp(self):
self.app = app
self.url_prefix = prefix = os.getenv("URL_PREFIX")
self.client = self.app.test_client()
def test_index(self):
response = self.client.get(self.url_prefix + '/')
self.assertEqual(response.status_code, 200)
if __name__ == '__main__':
unittest.main()
When I run TestUsers.py, I get ModuleNotFoundError: No module named 'project'. I tried doing sys.path.append('../') and ../../ inside of TestUsers.py, but that didn't help.

inside TestUsers.py, before importing app:
https://stackoverflow.com/a/22737042/7858114

I think you need an init.py in your apiproject folder too.

Python: unable to import classes from higher directory

I am learning flask. I have a directory structure that looks something like this.
project
- controllers
-- auth.py
-- main.py
- db
-- setup.py
- models
-- models.py
- templates
-- base.html
-- index.html
-- login.html
-- signup.html
-- 404.html
-__init__.py
The file init.py looks like this
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
# init SQLAlchemy so we can use it later in our models
db = SQLAlchemy()
def create_app():
app = Flask(__name__)
app.config['SECRET_KEY'] = '9OLWxND4o83j4K4iuopO'
app.config['SQLALCHEMY_DATABASE_URI'] = 'mysql://root:#localhost/mission_to_mars'
db.init_app(app)
# blueprint for auth routes in our app
from .controllers.auth import auth as auth_blueprint
app.register_blueprint(auth_blueprint)
# blueprint for non-auth parts of app
from .controllers.main import main as main_blueprint
app.register_blueprint(main_blueprint)
return app
I'm trying to import the db variable and create_app() function in controllers/auth.py, controllers/main.py, models/models.py, db/setup.py
I have tried the below syntaxes
from .. import db, create_app
which gives the error:
ImportError: attempted relative import with no known parent package
I have also tried
from project import db, create_app
which gives the error
ModuleNotFoundError: No module named 'project'
I want to know how I can import classes from different directories so that I can use them further in the project.
Thanks in advance

Why I can't import class declared in __init__.py?

I'm trying to clean up my flask app and I decided to use a boilerplate structure. I have the auth_bp blueprint, it's defined in auth.py , I have the following folder structure;
-app_root
-application
-__init__.py
- auth.py
- other files like template and static
- config.py (for configuration)
- server.py (to run the app through flask_script )
In __init__.py I have two classes: app and mail and I need to use them in my auth.py file.
But when I write :
from application import app, mail
I get an ImportError: cannot import name app
Here's the code in __init__.py:
from flask import Flask
from flask_mail import Mail
import config
from auth import auth_bp
app = Flask(__name__)
app.config.from_object("config.Config")
mail = Mail(app)
app.register_blueprint(auth_bp)
#app.route("/")
def home():
return "homepage"
Edit : Solved: I had to import auth after creating the app and mail object.

Import statement flow

My app layout
my_app
__init__.py
my_app
__init__.py
startup
__init__.py
create_app.py
create_users.py
common_settings.py
core
__init__.py
models.py
views.py
errors
__init__.py
errors.py
Inner __init__.py
from flask import Flask
from flask_script import Manager
from flask_sqlalchemy import SQLAlchemy
app = Flask(__name__) # The WSGI compliant web application object
db = SQLAlchemy(app) # Setup Flask-SQLAlchemy
manager = Manager(app) # Setup Flask-Script
from my_app.startup.create_app import create_app
create_app()
create_app.py
def create_app(extra_config_settings={}):
# Load all blueprints with their manager commands, models and views
from my_app import core
return app
core/__init__.py
# from . import views
views.py
from my_app import app, db
from flask import Flask, request
#app.errorhandler(Error)
def handle_invalid_usage(error):
response = jsonify(data=error.to_dict())
response.status_code = error.status_code
return response
I based this code on a tutorial I found. Everything works fine as long as I leave the __init__.py in the core folder empty.
When I don't, I get a NameError: name Error is not defined in my views.py. Error comes from errors.py.
I have three questions:
1) Why does this happen only when I leave the import statement in core/__init__.py.
2)
create_app.py
app.config.from_envvar('ENV_SETTINGS_FILE')
# Other app.config commands here
from my_app import core
return app
What happens when from my_app import core runs?
3) Finally when I return app, is this to ensure that Inner __init__.py file contains the updated app object?
Any explanations would be greatly appreciated!

Trying to build and configure an app with dynamic imports is really bad news and confusing for the reasons you are discovering. A much better and understandable pattern would be a more typical factory:
def create_app():
app = Flask(__name__)
configure_app(app, config)
register_db(app)
add_views(app)
add_manager(app)
return app
if __name__ == '__main__':
app = create_app()
app.run()
But since you're asking, your problem is here:
from my_app import app, db
from flask import Flask, request
#app.errorhandler(Error) # Error is not imported
def handle_invalid_usage(error):
response = jsonify(data=error.to_dict())
response.status_code = error.status_code
return response
The error occurs because views.py is imported, the code compiler comes across Error and cannot find a reference to it.
For your second question: from my_app import core causes core.__init.__ to run, which (presumably) adds the views onto the app object.