def append(self, x):
"""Add an item to the end of the list."""
_node = Node(x, None, None)
if self._head is not None: # if the head is not None the previously of new node become the tail and the
# next one None
_node._prev = self._tail # previously of new node linked to tail
_node._next = None # the next of new new node linked to None
self._tail._next = _node # the tail's next linked to new node
self._tail = _node # new node become the tail
else: # if the head is None there aren't node, so the new node is tail and the head
self._head = self._tail = _node
def insertbeforenode(self, data, value_search):
new_node = Node(data, None, None)
curr_node = self._head
while curr_node:
if curr_node._value == value_search._value:
new_node._prev = curr_node._prev
new_node._next = curr_node
curr_node._prev = new_node
new_node._prev._next = new_node # <--
break # find node and quit loop
else:
curr_node = curr_node._next