The google.appengine.api.users package provides the following exception classes:

exception Error()

This is the base class for all exceptions in this package.

exception UserNotFoundError()

Raised by the User constructor if no email_address is provided and the current user is not logged in.

exception RedirectTooLongError()

The redirect URL given to create_login_url() or create_logout_url() exceeds the maximum allowed length for a redirect URL.

exception NotAllowedError()

The federated_identity parameter was given to create_login_url(), but Federeated Login is not set. If you are getting this error you may need to change the Authentication Options to Federated Login in the Application Settings.