Print Level of each vertex from source

Breadth_First_Search.py

#Breadth-First-Search
#Unweighted Directed/Undirected graphs
class Node:
	def __init__(self , val):
		self.val = val
		self.next = None

class LinkedList:
	def __init__(self , head = None):
		self.head = head
	def insert(self , data):
		new_node = Node(data)
		new_node.next = self.head
		self.head = new_node
	def display(self):
		p = self.head
		while p != None:
			print ("{0} ".format(p.val))
			p = p.next

def bfs(adj , s):
	level = { s : 0}
	parent = {s : None}				#Recursively traversing parent of any node gives the shortest to that node from source
	frontier = [s]					
	i = 1
	while frontier:
		next = []
		for u in frontier:
			l = adj[u].head
			while l != None:
				if l.val not in level:
					level[l.val] = i
					parent[l.val] = u
					next.append(l.val)
				l = l.next
		i+=1
		frontier = next
	for i in level:
		print (str(i) , str(level[i]))			#Level of each node from source

if __name__ == '__main__':
		
	adj = []			
	mod_v = int(input("Number of Vertices"))
	for i in range(mod_v):
		finish = "n"
		list = LinkedList()
		print ("All adjacent vertices of vertex {0}".format(i))
		try:
			while True:
				vertex_data = int(input())
				list.insert(vertex_data)            #Press Ctrl-C to loop to next vertex
		except KeyboardInterrupt:
			pass
		adj.append(list)
	bfs(adj , 0)