Flask SqlAlchemy : Records not displayed

Here is my code :

from flask import Flask
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
from database_setup import Base, Restaurant, MenuItem

app = Flask(__name__)

engine = create_engine('sqlite:///restaurantmenu.db')
Base.metadata.bind = engine

DBSession = sessionmaker(bind=engine)
session = DBSession()


@app.route('/')
@app.route('/restaurants/<int:restaurant_id>/')
def restaurantMenu(restaurant_id):
    restaurant = session.query(Restaurant).filter_by(id=restaurant_id).one()
    items = session.query(MenuItem).filter_by(restaurant_id=restaurant.id)
    output = ''
    for i in items:
        output += i.name
        output += '</br>'
        output += i.price
        output += '</br>'
        output += i.description
        output += '</br>'
        output += '</br>'
    return output

if __name__ == '__main__':
    app.debug = True
    app.run(host='0.0.0.0', port=5000)

I run the file by entering the following URL :

localhost:5000/restaurants/2

And all I get is a blank page. I don't get any kind of error in my GitBash or browser or anywhere else.

I ran this simple code :

from flask import Flask
app = Flask(__name__)


@app.route('/')
@app.route('/hello')
def HelloWorld():
    return "Hello World"

if __name__ == '__main__':
    app.debug = True
    app.run(host='0.0.0.0', port=5000)

And this runs perfectly. What wrong am I doing ? TIA