W5Q2.py

class Node(object):
    def __init__(self, value):
        self.value=value
        self.next=None
        self.prev=None

class List(object):
    def __init__(self):
        self.head=None
        self.tail=None
    def insert(self,n,x):
        #Not actually perfect: how do we prepend to an existing list?
        if n!=None:
            x.next=n.next
            n.next=x
            x.prev=n
            if x.next!=None:
                x.next.prev=x              
        if self.head==None:
            self.head=self.tail=x
            x.prev=x.next=None
        elif self.tail==n:
            self.tail=x
    def delete(self,nvalue):
        node = self.head
        prevNode = None
        while node != None:
            if node.value == nvalue:    #if node is one to delete
                if prevNode != None:    #to avoid error in removing first node do check
                    prevNode.next = node.next   
                else:
                    self.head = node.next
            prevNode = node             #changes value of prevNode each iteration
            node = node.next            #changes value of node each iteration
            
    def display(self):
        values=[]
        n=self.head
        while n!=None:
            values.append(str(n.value))
            n=n.next
        print ("List: ",",".join(values))
          
if __name__ == '__main__':
    l=List()
    l.insert(None, Node(4))
    l.insert(l.head,Node(6))
    l.insert(l.head,Node(8))
    l.display()