array = [["A",1],
         ["B",2],
         ["C", None],
         [None,None],
         [None,None],
         [None,None],
         [None,None]]

header = 0
free = 3

def traverse(array):
    pointer = 1
    while pointer != None:
        node = array[pointer]
        data = node[0]
        print(data)
        pointer = node[1]

def append(newdata):
    global free
    newnode = array[free]
    newnode[0] = newdata

    pointer = header
    while pointer != None:
        node = array[pointer]
        pointer = node[1]

    node[1] = free
    free = free + 1
    
choice = ''
while choice != 'X':

    print(' A | Traverse')
    print(' B | Append')
    choice = input('enter')

    if choice == 'A':
        traverse(array)
    if choice == 'B':
        data = input('enter a data value')
        append(data)