[web2py] too many redirect during checking condition

[黄祥]

hi,

i want to use condition that if user not log in will redirect to login
page, and if logged in will redirect to index page, heres my
controller :

if not session.authorized:
        redirect(URL('user'))
else:
        redirect(URL('index'))

def index():
    return dict(message=T('Hello World'))

def user():
    return dict(form = auth())

i know there is a mistook code on my own, could there anybody show me
where is the wrong part?
i've tried the other code too, but got the same result :

if not auth.is_logged_in():
        redirect(URL('user'))
else:
        redirect(URL('index'))

def index():
    return dict(message=T('Hello World'))

def user():
    return dict(form = auth())

thank you so much before