This if check is not necessary. If they pass in an empty iterable, e.g. empty list, it will iterate over nothing and do nothing with it. If it's not an iterable, you'll get the expected TypeError.
You currently have kind of a weird situation where this would work:
DblLinkedList(True)
This if check is not necessary. If they pass in an empty iterable, e.g. empty list, it will iterate over nothing and do nothing with it. If it's not an iterable, you'll get the expected TypeError.
You currently have kind of a weird situation where this would work: DblLinkedList(True)
but this would not work: DblLinkedList(False)