STD_5.py

class Node:
    def __init__(self, dataval = None):
        self.dataval = dataval
        self.nextval = None

class SLinkedList:
    '''
    CLass for Linked List, made of Nodes which have Values and reference to the next Node, 
    Class attributes: allValues - a list of all the possible values inside a linked list 
    '''
    def __init__(self):
        self.headval = None
      
    def listprint(self):
        printval = self.headval
        while printval is not None:
            print (printval.dataval)
            printval = printval.nextval
            
    def AtBeginning(self,newdata):
        NewNode = Node(newdata)

    def AtEnd(self, newdata):
        NewNode = Node(newdata)
        if self.headval is None:
            self.headval = NewNode
            return
        last = self.headval
        while(last.nextval):
            last = last.nextval
        last.nextval = NewNode
      

    def Insert(self,val_before,newdata):
      '''
      Class method for inserting values inside the linked list
      Input: any type. Two values- a value of a node after which new value will be inserted, and value of the new node to be inserted into the linked list
      Output: boolean. True if val_before argument had been found in a linked list, False if it had not or value of val_before is None
      '''
      if val_before is None:                    #if value of val_before variable is None
        print("No node to insert after")
        return False
      else:                                     #if value of val_before variable is not None
        curVal = self.headval                   #create curVal variable and set it to the firs value of the linked list
        while curVal != None:                   #repeat until value of curVal is None
          if curVal.dataval == val_before:      #if data attribute of curVal Node is equal to the value of val_before parameter
            oldNextVal = curVal.nextval         #create old next value variable and set it to a reference to the Node referenced in curVal Node nextval attribute
            curVal.nextval = Node(newdata)      #set curVal Node nextval attribute to an instance of Node class with newdata parameter passed as argument
            curVal.nextval.nextval = oldNextVal #set value of nextval attibute of the Node referenced in curVal Node nextval attribute to Node reference stored in oldNextVal variable
            return True
          curVal = curVal.nextval               #set curVal variable to the value of curVal nextval attribute
        return False
        
list = SLinkedList()


list.headval = Node("Mon")

e2 = Node("Tue")
e3 = Node("Thur")
e4 = Node("Fri")
e5 = Node("Sat")
list.headval.nextval = e2
e2.nextval = e3
e3.nextval = e4
e4.nextval = e5



list.AtEnd("Sun")

list.listprint()
list.Insert("Tue","Weds")
print("\n\nInserted List:")
list.listprint()

#In insert I had deleted two arguments out of three because there is no reason for them to be there, these arguments have to be calculated, which means that we would need an extra method that only provides these values
#The method had been generalized, as it still solves the task given, but does additional work by adding all of the days instead of only one. Just in case I have added additional commented code, which when uncommented, will solve the task as specified
#In Insert function I avoid hard coding values like weekdays inside the Class in order to make it reusable