link those lists

class Node:
	def __init__(self, value):
		self._value = value
		self._prev = None
		self._next = None

	def getValue(self):
		return self._value

class LinkedList:
	def __init__(self):
		self._header = Node(None)
		self._trailer = Node(None)

		self._header.next = self._trailer
		self._trailer.next = self._header

		self._size = 0

	def __str__(self):
		if self._size == 0:
			return "empty linkedlist"

		string = ""
		current = self._header._next
		while current is not self._trailer:
			string += str(current.getValue()) + " "
			current = current._next

		return string

	def add(self, value, index):
		# special case: outta bounds
		if index > self._size or index < 0:
			print("outta bounds :(")
			return

		newNode = Node(value)

		# special case: empty list
		if self._size == 0:
			self._insert(self._header, newNode, self._trailer)
			self._size += 1
			return

		# general case
		before = self._header
		for i in range(index):
			before = before._next
		after = before._next
		self._insert(before, newNode, after)
		self._size += 1
		return

	def _insert(self, before, thing, after):
		thing._prev = before
		thing._next = after
		before._next = thing
		after._prev = thing