pagerank.py

'''
Author: https://github.com/bhushan-borole
'''
'''
The input graph for the algorithm is:

  A B C
A 0 1 1
B 0 0 1
C 1 0 0

'''

graph = [[0, 1, 1],
    	[0, 0, 1],
    	[1, 0, 0]]


class Node:
    def __init__(self, name):
        self.name = name
        self.inbound = []
        self.outbound = []
    
    def add_inbound(self, node):
        self.inbound.append(node)
    
    def add_outbound(self, node):
        self.outbound.append(node)
    
    def __repr__(self):
        return 'Node {}: Inbound: {} ; Outbound: {}'.format(self.name,
                                                      	self.inbound,
                                                      	self.outbound)


def page_rank(nodes, limit=3, d=0.85):
    ranks = {}
    for node in nodes:
        ranks[node.name] = 1

    outbounds = {}
    for node in nodes:
        outbounds[node.name] = len(node.outbound)

    for i in range(limit):
        print("======= Iteration {} =======".format(i+1))
        for j, node in enumerate(nodes):
            ranks[node.name] = (1 - d) + d * sum([ ranks[ib]/outbounds[ib] for ib in node.inbound ])
        print(ranks)


def main():
    names = list(input('Enter Names of the Nodes: ').split())

    nodes = [Node(name) for name in names]
    
    for ri, row in enumerate(graph):
        for ci, col in enumerate(row):
            if col == 1:
                nodes[ci].add_inbound(names[ri])
                nodes[ri].add_outbound(names[ci])

    print("======= Nodes =======")
    for node in nodes:
        print(node)

    page_rank(nodes)


if __name__ == '__main__':
    main()