Just a small exercise I wrote for myself a while ago. Plenty of room for improvement!

node_reader

simple = [['a','b','once'], ['b','c','upon'], ['c','d','a time']]
double = [['a','0','b','once again'], ['b','a','c','upon'], ['c','b','0','a time']]
simpled = {'a':['0','once'], 'b':['a', 'upon'], 'c':['b', 'a dictionary']}

def readsimple(start, nodes):
    for item in nodes:
        x = item[1]
        if item[0] == start:
            print item[0], item[-1]
            readsimple(x, nodes)
        else:
            pass

def readsimpled(simpled):
    nodenames = simpled.keys()
    traceback = []
    progression = []
    print "Node names:", nodenames
    for x in nodenames:
        y = simpled[x]
        z = [x, y[0]]
        traceback.append(z)
    print "Trace back:", traceback
    for item in traceback:
        if item[1] == '0':
            startNode = item[0]
            progression.insert(0, startNode)
        else:
            pass
    print "Start node:", startNode
    while len(nodenames) > len(progression):
        x = traceback.pop()
        if x[1] == progression[-1]:
            progression.append(x[0])
            print "found progression:", x[1], "-->", x[0]
        else:
            traceback.insert(0,x)
    print "Progression:", progression
    readout = []
    for elem in progression:
        temp = simpled[elem]
        readout.append(temp[1])
    print "Readout:"
    for i in readout:
        print i
    

def readdouble(nodes):
    predecessor = '0'
    successor = 'whatever'
    while successor != '0':
        for item in nodes:
            if item[1] == predecessor:
                print item[0], item[-1]
                predecessor = item[0]
                successor = item[2]
            else:
                pass
            


if __name__ == "__main__":
    readsimpled(simpled)