Question

class SLinkedList:
"""Singly linked list with access to front and end, and with stored size.
"""

#-------------------------- nested _Node class --------------------------
class _Node:
__slots__ = '_element', '_next' # streamline memory usage

def __init__(self, element, next):
self._element = element
self._next = next

#------------------------------- queue methods -------------------------------
def __init__(self):
"""Create an empty list."""
self._head = None
self._tail = None
self._size = 0

def __len__(self):
"""Return the number of elements in the list."""
return self._size

def isEmpty(self):
"""Return True if the list is empty."""
return self._size == 0
  
# READ THIS!
def __repr__(self):
plist = []
current = self._head
# This is how to traverse a list:
while current != None: # use a while-loop.
plist.append(current._element) # process the stored element.
current = current._next # jump to the next node.
return "SLinkedList(%s)" % repr(plist)

def first(self):
"""Return but do not remove the first element.
Raise EmptyError if the list is empty.
"""
if self.isEmpty():
raise EmptyError('The SLinkedList is empty')
return self._head._element
  
def deleteFirst(self):
"""Remove and return the first element.
Raise EmptyError if the list is empty.
"""
if self.isEmpty():
raise EmptyError('The SLinkedList is empty')
answer = self._head._element
self._head = self._head._next
self._size -= 1
if self.isEmpty(): # special case when list is empty
self._tail = None # removed head had been the tail
return answer
  
def addFirst(self, e):
"""Add element e to the front of the list."""
self._head = self._Node(e, self._head) # create and link a new node
if self._tail == None: # special case when list was empty
self._tail = self._head # added head is the tail
self._size += 1
  
def addLast(self, e):
"""Add e to the end of the list."""
newest = self._Node(e, None) # node will be new tail node
if self.isEmpty():
self._head = newest # special case: previously empty
else:
self._tail._next = newest
self._tail = newest # update reference to tail node
self._size += 1
  
def last(self):
"""Return but do not remove the last element.
Raise EmptyError if the list is empty.
"""
if self.isEmpty():
raise EmptyError('The SLinkedList is empty')
return self._tail._element
  
def _nodeAtIndex(self, index):
"""Returns the reference to the node at the given index;
If index is out of range, raise IndexError
"""
# PROBLEM 2
# You can assume that index is non-negative.
# You need to traverse the list and stop at the required index.
# YOUR CODE HERE
raise NotImplementedError()
  
def __getitem__(self, index):
aNode = self._nodeAtIndex(index)
return aNode._element
  
def __setitem__(self, index, value):
# PROBLEM 3
# YOUR CODE HERE
raise NotImplementedError()
  
def deleteLast(self):
"""Remove and return the last element. Runs in O(n) time.
Raise EmptyError if the list is empty.
"""
# PROBLEM 4
# Your code should handle three cases:
# a list of size 0, size 1 and size >=2.
# If the list is of size >= 2
# you need to traverse the list and stop at the second last node;
# that node contains a reference to the last node;
# this reference needs to be copied/assigned to self._tail
# YOUR CODE HERE
  

Answer 1

Complete code

# coding=utf-8
import pytest

class SLinkedList:
"""Singly linked list with access to front and end, and with stored size."""

#-------------------------- nested _Node class --------------------------
class _Node:
__slots__ = '_element', '_next' # streamline memory usage

def __init__(self, element, next):
self._element = element
self._next = next

#------------------------------- queue methods -------------------------------
def __init__(self):
"""Create an empty list."""
self._head = None
self._tail = None
self._size = 0

def __len__(self):
"""Return the number of elements in the list."""
return self._size

def isEmpty(self):
"""Return True if the list is empty."""
return self._size == 0

# READ THIS!
def __repr__(self):
plist = []
current = self._head
# This is how to traverse a list:
while current != None: # use a while-loop.
plist.append(current._element) # process the stored element.
current = current._next # jump to the next node.
return "SLinkedList(%s)" % repr(plist)

def first(self):
"""Return but do not remove the first element.
Raise EmptyError if the list is empty.
"""
if self.isEmpty():
raise EmptyError('The SLinkedList is empty')
return self._head._element

def deleteFirst(self):
"""Remove and return the first element.
Raise EmptyError if the list is empty.
"""
if self.isEmpty():
raise EmptyError('The SLinkedList is empty')
answer = self._head._element
self._head = self._head._next
self._size -= 1
if self.isEmpty(): # special case when list is empty
self._tail = None # removed head had been the tail
return answer

def addFirst(self, e):
"""Add element e to the front of the list."""
self._head = self._Node(e, self._head) # create and link a new node
if self._tail == None: # special case when list was empty
self._tail = self._head # added head is the tail
self._size += 1

def addLast(self, e):
"""Add e to the end of the list."""
newest = self._Node(e, None) # node will be new tail node
if self.isEmpty():
self._head = newest # special case: previously empty
else:
self._tail._next = newest
self._tail = newest # update reference to tail node
self._size += 1

def last(self):
"""Return but do not remove the last element.
Raise EmptyError if the list is empty.
"""
if self.isEmpty():
raise EmptyError('The SLinkedList is empty')
return self._tail._element

def _nodeAtIndex(self, index):
"""Returns the reference to the node at the given index;
If index is out of range, raise IndexError
"""

if(self.isEmpty() or index>=self._size):
raise IndexError("Index out of range")
temp=self._head
i=0
while i!=index:
temp=temp._next
i+=1
return temp

def __getitem__(self, index):
aNode = self._nodeAtIndex(index)
return aNode._element

def __setitem__(self, index, value):
if(index>self._size):
raise IndexError("Index out of range")
if index==0:
self.addFirst(value)
return
temp=self._head._next
i=1
while i!=index:
temp=temp._next
i+=1
temp._element=value

def deleteLast(self):
"""Remove and return the last element. Runs in O(n) time.
Raise EmptyError if the list is empty.
"""
if self.isEmpty():
raise EmptyError('The SLinkedList is empty')
self._size -= 1
if self._head.next==None:
value=self._head._element
self._head=self._tail=None
return value
temp=self._head
while temp._next._next!=None:
temp=temp._next
value=temp._next._element
tail=temp
tail._next=None
return value

Code snaps for indent

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