def insert(self, item_new, pos):
"""given an item and a position, this method insert an item at the position required"""
actual_position = 0
previous_position = None
current = self.head
new_node = Node(None, item_new)
while actual_position != pos and current is not None:
previous_position = current
current = current.next
actual_position += 1
if actual_position != pos:
raise ValueError("Invalid Position %d" % pos)
previous_position.next = new_node
new_node.next = current
new_node.previous = previous_position
if current is None:
self.tail = new_node
else:
current.previous = new_node
return self
