AttributeError: 'NoneType' object has no attribute 'route' (app not created)

7 Dec 2025

1 min read

AttributeError: None route

$ flask run
Traceback (most recent call last):
  ...
AttributeError: 'NoneType' object has no attribute 'route'

Why this happens

If app is None due to failed initialization or incorrect ordering (using @app.route before assigning app), decorators will attempt to call route on None.

Fix

Create the app first, then declare routes.
For factories, don’t decorate at import time; register routes inside create_app().

Wrong code

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

from flask import Flask
app = Flask(__name__)

Fixed code

from flask import Flask
app = Flask(__name__)

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