class List_Node:
    # self.data
    # self.next

    # constructor
    def __init__(self, data):
        self.data = data
        self.next = None

    # Called when printing the object
    def __str__(self):
        return str(self.data)

    def go_wave(self):
        self.data = self.data + " -- go wave!"


    def print_linked_list_pretty(self):
        # self is front node of list

        current=self
        while(current!=None):
            print current, "->",
            current = current.next
        print "None"    

def print_linked_list(L):
    # L is front node of list

    current=L
    while(current!=None):
        print current # prints current.__str__()
        current = current.next

    
x = List_Node('a')
print x.data
print x   # calls __str__() method

x.go_wave()
print x

print

# Create L: 'a'->'b'->'c'->'d'->None
L=List_Node('a') # L: 'a' -> None
L.next=List_Node('b')
L.next.next=List_Node('c')
L.next.next.next=List_Node('d')

print_linked_list(L)
L.print_linked_list_pretty()