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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def post_login(self, came_from=lurl('/')):
 """ Redirect the user to the initially requested page on successful authentication or redirect her back to the login page if login failed. """

        if not request.identity:
            login_counter = request.environ.get('repoze.who.logins', 0) + 1
            redirect('/login',
                params=dict(came_from=came_from, __logins=login_counter))
        userid = request.identity['repoze.who.userid']
        flash(_('Welcome back, %s!') % userid)
        redirect(came_from)