Look for the class in .extensions in case it has already been
    imported (perhaps as a builtin extensions hard compiled into unity_server).

def _create_class_instance(class_name, _proxy):
    """
    Look for the class in .extensions in case it has already been
    imported (perhaps as a builtin extensions hard compiled into unity_server).
    """
    try:
        return _class_instance_from_name('turicreate.extensions.' + class_name, _proxy=_proxy)
    except:
        pass
    return _class_instance_from_name(class_name, _proxy=_proxy)