Example of Floyd algorithm for loop detection

loop_detection.py

'''
Example of Floyd algorithm for loop detection
'''

class Node :
	def __init__(self, data) :
		self.next = None
		self.data = data

	def __str__(self) :
		return str(self.data)

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

	def add_node(self, data):
		if self.head == None :
			self.head = Node(data)
		else :
			tmp = Node(data)
			tmp.next = self.head
			self.head = tmp

	def add_loop(self, f, t) :
		node = self.head
		i = 0
		node_f = None
		node_t = None
		while node != None :
			i += 1
			if i == f :
				node_f = node
			if i == t :
				node_t = node 
			node = node.next
		node_f.next = node_t

	def print_list(self):
		node = self.head
		while node != None :
			print node.data
			node = node.next

def toirtoise_and_hare(l) :
	tortoise = l.head
	hare = l.head
	steps = 0
	while True:
		if hare == None :
			return (steps, 'No loop found')				
		hare = hare.next
		if hare == None :
			return (steps, 'No loop found')
		hare = hare.next
		tortoise = tortoise.next
		if hare == tortoise:
			#print hare, tortoise
			return (steps, 'Loop found')
		steps += 1
		
l = LinkedList()
for i in xrange(1000) :
	l.add_node(i)

l.add_loop(800, 200)

print toirtoise_and_hare(l)
#l.print_list()

I don't understand how this is working, because the list type has no method "head", and no method "next".