在python的链表中实现附加功能

Question

I am trying to write the list.append() operation in python. I implemented a linked list and it work fine. But I am not getting the last data item to be printed. When I try to print all the items in the list I get all the data value inside the node printed except the last one. I get 'None' printed instead of the value. I'm making some mistake in assigning the next pointer to 'None' in the newly added node. Need help in fixing.

Implementation of Node class and List class.

class Node:
   def __init__(self,item):
      self.data = item
      self.next = None
   def getData(self):
      return self.data
   def getNext(self):
      return self.next
   def setData(self,newItem):
      self.data = newItem
   def setNext(self, newNext):
      self.next = newNext
class UnorderedList:
   def __init__(self):
       self.head = None
   def isEmpty(self):
       return self.head == None
   def add(self,item):
       temp = Node(item)
       temp.setNext(self.head)
       self.head = temp
   def size(self):
       count = 0
       current = self.head
       while current != None:
          count = count + 1
          current = current.getNext()
    def append(self, item):
       current = self.head
       isEnd = False
       newItem = Node(item)
       while not isEnd:
          if current.getNext() == None:
              isEnd = True
          else:
              current = current.getNext()
      current = current.setNext(newItem)
      newItem = current.getNext()
  def printList(self):
      current = self.head
      isEnd = False
      while not isEnd:
          if current.getNext() == None:
              isEnd = True
          else:
              print current.getData()
              current = current.getNext()

I create an object and pass values.

mylist = UnorderedList()
mylist.add(31)
mylist.add(77)
mylist.add(17)
mylist.add(93)
mylist.add(26)
mylist.add(54)
print(mylist.size())
mylist.append(12)
print(mylist.size())
mylist.append(15)
print(mylist.size())
print('\n')
print mylist.printList()

Output is:

6
7
8

54
26
93
17
77
31
12
None

Answer 1

The problem is you are doing

print(mylist.printList())

while printList() doesn't actually return anything. That's the last None printed there.

Hope this helps:

current = self.head
while(current!=None):
      print(current.getData())
      current=current.getNext()

This should be placed inside printlist.

And called this way :

mylist.printlist()
54
26
93
17
77
31
12
15

Edit : I had also modified your append function to :

def append(self, item):
    print("append",item)
    current = self.head
    isEnd = False
    newItem = Node(item)
    while not isEnd:
        if current.getNext() == None:
            isEnd = True
        else:
            current = current.getNext()
    print("\Appending to",current.getData())
    current.setNext(newItem)
    current=current.getNext()
    print("\tAppended",current.getData())