Breadth-First-Search

[MontyPython]

Hello Python-Forum,

I'm new to this Forum and very new to Python and programming itself.
We got a homework in our course where we have to implement the breadth-first-search in Python. We also got a script which we have to fill. We have to use classes.
My fellow students and my have got some really big problems with this homework :(
I hope you can help us to solve this task.


Here is the code we got to fill:

import math, queue

class Graph:
    ''' Class Graph.
    Implements an undirected graph, in the form {v: [w1,w2]} for
    edges (v,w1), (v,w2), i.e., adjacency lists.
    Provides a dict "node", with the nodes as keys, to save additional attributes.'''
    def __init__(self):
        self.graph = {}
        self.node = {}
        
    def __iter__(self):
        '''allows to iterate over nodes by "for v in class instances".'''
        return iter(self.graph)
    
    def __len__(self):
        '''returns the number of nodes as len(class instance)'''
        return(len(self.graph))
        
    def add_nodes(self, L):
        '''adds all nodes in list L to graph and intializes their node dict'''
        #TODO
        pass
    
    def has_edge(self, e):
        '''returns True if the tuple e is an edge, False otherwise'''
        #TODO
        pass
    
    def add_edges(self, L):
        '''adds all edge-tuples in the list L to the graph'''
        #TODO
        pass
    
    def number_of_edges(self):
        '''returns the number of edges in the graph'''
        #TODO
        pass
    
    def neighbours(self,v):
        '''returns a list of all neighbours of v'''
        #TODO
        pass


def BFS_init(G, s):
    '''Initializes node dicts in graph class G for color, distance, and predecessor.'''
    for v in G:
        G.node[v]['color'] = 'white'
        G.node[v]['dist'] = float('inf')
        G.node[v]['pi'] = None
    G.node[s]['color'] = 'gray'
    G.node[s]['dist'] = 0
    
        
def BFS(G, s):
    '''Function BFS. Expects a graph class with node attributes and starting node s.
    Implements BFS and saves distances in corresponding node dicts.'''

    BFS_init(G, s)
    
    #TODO

Best regards