lapp/update_db.py

from lapp import create_app
import sqlalchemy as sa
from models import db, Item

app = create_app()
app.app_context().push()
query = sa.select(Item).where(Item.quantity == 0)
items = db.session.scalars(query).all()

# items=Item.query.filter_by(quantity='').all()
for i in items:
    print(f"{i.label} {i.quantity} {i.unit}")