pagerank, the simple case

pagerank.py

def computePR(graph, oldPR):
    newPR = {}
    N = len(graph)
    for node in graph:
        pr = 0
        for pred in graph[node][0]:
            if len(graph[pred][1]) != 0:
                pr += (oldPR[pred]+0.0)/len(graph[pred][1])
        pr = 0.15 / N + 0.85 * pr
        newPR[node] = pr
    return newPR

#each node in graph is with two lists, 
#node[0] is the list of incoming nodes, 
#node[1] is the list of outgoing nodes.
graph = {1:[[2,3],[2,3]],2:[[1],[1]],3:[[1],[1]]}
oldPR = {}
for node in graph:
    oldPR[node] = 1.0/len(graph)

for i in range(50):
    newPR = computePR(graph, oldPR)
    print newPR
    oldPR,newPR = newPR, oldPR