Double linking array in Python

Question

Since I'm pretty new this question'll certainly sound stupid but I have no idea about how to approach this.

I'm trying take a list of nodes and for each of the nodes I want to create an array of predecessors and successors in the ordered array of all nodes.

Currently my code looks like this:

    nodes = self.peers.keys()
    nodes.sort()

    peers = {}
    numPeers = len(nodes)
    for i in nodes:
        peers[i] = [self.coordinator]
    for i in range(0,len(nodes)):
        peers[nodes[i%numPeers]].append(nodes[(i+1)%numPeers])
        peers[nodes[(i+1)%numPeers]].append(nodes[i%numPeers])
#        peers[nodes[i%numPeers]].append(nodes[(i+4)%numPeers])
#        peers[nodes[(i+4)%numPeers]].append(nodes[i%numPeers])

The last two lines should later be used to create a skip graph, but that's not really important. The problem is that it doesn't really work reliably, sometimes a predecessor or a successor is skipped, and instead the next one is used, and so forth. Is this correct at all or is there a better way to do this? Basically I need to get the array indices with certain offsets from each other.

Any ideas?

Answer 1

I would almost bet that when the error occurs, the values in nodes have duplicates, which would cause your dictionary in peers to get mixed up. Your code assumes the values in nodes are unique.