bfs.py

import collections

class graph:
    def __init__(self,gdict=None):
        if gdict is None:
            gdict = {}
        self.gdict = gdict

def bfs(graph, startnode):
# Track the visited and unvisited nodes using queue
        seen, queue = set([startnode]), collections.deque([startnode])
        while queue:
            vertex = queue.popleft()
            marked(vertex)
            for node in graph[vertex]:
                if node not in seen:
                    seen.add(node)
                    queue.append(node)

def marked(n):
    print(n)

if __name__=="__main__": 

    gdict = { "a" : set(["b","c"]),
                    "b" : set(["a", "d"]),
                    "c" : set(["a", "d"]),
                    "d" : set(["e"]),
                    "e" : set(["a"])
                    }

    bfs(gdict, "a")