Question

I need to implement Dijkstra’s Algorithm in Python. However, I have to use a 2D array to hold three pieces of information – predecessor, length and unvisited/visited.
I know in C a Struct can be used, though I am stuck on how I can do a similar thing in Python, I am told it’s possible but I have no idea to be honest

Answer 1

As mentioned above, you can use an instance of an object.

This author has a pretty convincing python implementation of Dijkstras in python.

#
# This file contains the Python code from Program 16.16 of
# "Data Structures and Algorithms
# with Object-Oriented Design Patterns in Python"
# by Bruno R. Preiss.
#
# Copyright (c) 2003 by Bruno R. Preiss, P.Eng.  All rights reserved.
#
# http://www.brpreiss.com/books/opus7/programs/pgm16_16.txt
#
class Algorithms(object):

    def DijkstrasAlgorithm(g, s):
        n = g.numberOfVertices
        table = Array(n)
        for v in xrange(n):
            table[v] = Algorithms.Entry()
        table[s].distance = 0
        queue = BinaryHeap(g.numberOfEdges)
        queue.enqueue(Association(0, g[s]))
        while not queue.isEmpty:
            assoc = queue.dequeueMin()
            v0 = assoc.value
            if not table[v0.number].known:
                table[v0.number].known = True
                for e in v0.emanatingEdges:
                    v1 = e.mateOf(v0)
                    d = table[v0.number].distance + e.weight
                    if table[v1.number].distance > d:

                        table[v1.number].distance = d
                        table[v1.number].predecessor = v0.number
                        queue.enqueue(Association(d, v1))
        result = DigraphAsLists(n)
        for v in xrange(n):
            result.addVertex(v, table[v].distance)
        for v in xrange(n):
            if v != s:
                result.addEdge(v, table[v].predecessor)
        return result
    DijkstrasAlgorithm = staticmethod(DijkstrasAlgorithm)

Notice those pieces of information are ‘held’ in the object he is constructing by calling Algorithms.Entry(). Entry is a class and is defined like this:

class Entry(object):
    """
    Data structure used in Dijkstra's and Prim's algorithms.
    """

    def __init__(self):
        """
        (Algorithms.Entry) -> None
        Constructor.
        """
        self.known = False
        self.distance = sys.maxint
        self.predecessor = sys.maxint

The self.known, self.distance… are those pieces of information. He does not set these explicit in the constructor (init) but sets them later. In Python you can access attributes with dot notation. for examle: myObject= Entry(). the myObject.known, myObject.distance… they are all public.