class graph (object) :
    def __init__(self, n) :
        """constructor for the graph class.
        takes a single parameter which is the number of nodes
        in the graph
        """
        # set the number of nodes
        self.n = n
        # the number of edges
        self.m = 0
        # the adjacency matrix
        self.matrix = [ [0 for i in range(n)] for i in range(n) ]
        # a dictionary that maps node ids to their indices
        self.node_id_map = {}

    def __len__(self) :
        return self.n

    def num_paths(self, node1, node2, k) :
        """
        returns the number of paths of length AT MOST k 
        between node1 and node2
        node1 and node2 are the names of the two nodes as they
        appear in the input file that contains the graph
        """
        pass


def load_dot(file_name) :

    file_handle = open(file_name, 'U')
    file_handle.readline()
    n = 0 # the number of nodes
    # first you need to process the dot file to determine
    # the number of nodes in the graph
    g = graph(n)
    file_handle.seek(0)
    # go back to the beginning of the file
    file_handle.readline()
    for line in file_handle :
        pass
        # process each edge
    return g

if __name__ == '__main__' :
    g = load_dot('test.dot')
    print g.num_paths('a', 'b', 2)