Python decorator function to require login.

login_required.py

def login_required(f):
    """
    Decorate routes to require login.
    http://flask.pocoo.org/docs/1.0/patterns/viewdecorators/
    """
    @wraps(f)
    def decorated_function(*args, **kwargs):
        if session.get("user_id") is None:
            return redirect("/")
        return f(*args, **kwargs)
    return decorated_function