Flask current_user function to load the user only when needed

gistfile1.py

def current_user():
    try:
        return g.current_user
    except RuntimeError:
        return None
    except AttributeError:
        try:
            g.current_user = db.query(User).get(session['user_id'])
        except KeyError:
            g.current_user = None
        return g.current_user