def append(self, new_data):
new_node = Node(data = new_data)
new_node.next = None # at the last
last = self.tail
# if list is empty then this is the first node
if last is None:
new_node.prev = None
self.head = new_node
return
last.next = new_node
new_node.prev = last
def push(self, new_data):
new_node = Node(data = new_data)
new_node.prev = None # at the beginning
new_node.next = self.head
if self.head is not None:
self.head.prev = new_node
self.head = new_node
def insert_before(self, next_node, new_data):
if next_node is None:
print("Error: given next_node is None")
return
new_node = Node(data = new_data)
new_node.next = next_node
new_node.prev = next_node.prev
if new_node.prev is not None: # if new_node.prev (next_node.prev) is None it means we are at the beginning of the list
new_node.prev.next = new_node
next_node.prev = new_node
def insert_after(self, prev_node, new_data):
if prev_node is None:
print("Error: given prev_node is None")
return
new_node = Node(data = new_data)
new_node.prev = prev_node
new_node.next = prev_node.next
if new_node.next is not None: # if new_node.next (prev_node.next) is None it means we are at the end of the list
new_node.next.prev = new_node
prev_node.next = new_node