def label(model_class, sep='.'):
    """
    Returns a string label for the model class. eg auth.User
    """
    if hasattr(model_class._meta, 'model_name'):
        model_name = model_class._meta.model_name
    else:
        model_name = model_class._meta.module_name
    return '{}{}{}'.format(model_class._meta.app_label, sep, model_name)

    Returns a string label for the model class. eg auth.User
    
actstream/registry.py