<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def add_user_grant(self, permission, user_id):
 """ Convenience method that provides a quick way to add a canonical user grant to a key. This method retrieves the current ACL, creates a new grant based on the parameters passed in, adds that grant to the ACL and then PUT's the new ACL back to GS. :type permission: string :param permission: The permission being granted. Should be one of: READ|FULL_CONTROL See http://code.google.com/apis/storage/docs/developer-guide.html#authorization for more details on permissions. :type user_id: string :param user_id: The canonical user id associated with the GS account to which you are granting the permission. """

        acl = self.get_acl()
        acl.add_user_grant(permission, user_id)
        self.set_acl(acl)