class Empty(Exception):
pass
class Linklist:
class _Node:
# Nonpublic class for storing a linked node
__slots__='_element','_next'
def __init__(self,ele,ne):
self._element=ele
self._next=ne
def __init__(self):
self._head=None
self._size=0
self._tail=None
def __len__(self):
return self._size
def is_empty(self):
return self._size==0
def add_first(self,e):
self._head=self._Node(e,self._head)
if self._size==0:
self._tail=self._head
self._size+=1
def add_last(self,e):
newlastnode=self._Node(e,None)
if ~self.is_empty():
self._tail._next=newlastnode
self._tail=newlastnode
else:
self._tail=newlastnode
self._size+=1
def remove_first(self):
if self.is_empty():
raise Empty("The linked is empty")
self._head=self._head._next
self._size-=1
