class List():
    def __init__(self):
        self.head = None

    def last(self):
        if self.head == None:
            return None
        else:
            last = self.head
            while True:
                if last.next() == None:
                    return last
                else:
                    last = last.next()

    def len(self):
        len = 1
        if self.head == None:
            return 0
        else:
            last = self.head
            while True:
                if last.next() == None:
                    return len
                else:
                    last = last.next()
                    len += 1

    def add(self, data):             #=append()
        if self.head == None:
            self.head = Knot(data)
        else:
            last = self.last()
            last.add(Knot(data))

    def remove(self, index):
        knotDel = self.findIndex(index)
        knotChange = self.findIndex(index - 1)

        knotChange.pointer = knotDel.pointer
        knotDel = None

    def change(self, index, data):
        knot = self.findIndex(index)
        knot.data = data

    def findIndex(self, nr):
        try:
            index = self.head
            for i in range(nr):
                index = index.next()
            return index
        except:
            print("Index nicht in Liste")

    def printWhole(self):
        if self.head == None:
            print(None)
            return
        
        knot = self.head

        while True:
            if knot.next() == None:
                print(knot.data)
                return
            else:
                print(knot.data)
                knot = knot.next()

    def print(self, index):
        knot = self.findIndex(index)
        print(knot.data)


class Knot():
    def __init__(self, data):
        self.data = data
        self.pointer = None

    def add(self, obj):
        if self.pointer == None:
            self.pointer = obj

    def next(self):
        return self.pointer