'Raise an error if the item is NOT accessible to user, otherwise return the item.
:raises exceptions.ItemAccessibilityException:'

def error_unless_accessible(self, item, user, **kwargs):

    if self.is_accessible(item, user, **kwargs):
        return item
    raise exceptions.ItemAccessibilityException(('%s    is    not    accessible    by    user' % self.model_class.__name__))
