Dijkstra in Python

Here is a complete version of Python2.7 code regarding the problematic original version. Just paste in in any .py file and run.
Output: The storage objects are pretty clear; dijkstra algorithm returns with first dict of shortest distance from source_node to {target_node: distance length} and second dict of the predecessor of each node, i.e. {2:1} means the predecessor for node 2 is 1 --> we then are able to reverse the process and obtain the path from source node to every other node.

For example, we have {5:2} and {2:1}, which renders that the path from source node 1 to 5 is 1-->2-->5.

And the return output should be :
nodes: set([1, 2, 3, 4, 5, 6, 7, 8])
edges: defaultdict(<type 'list'>, {1: [2, 3], 2: [1, 4, 5], 3: [1, 6, 7], 4: [2, 8], 5: [2, 8], 6: [3, 7], 7: [3, 6], 8: [4, 5]})
distances: {(1, 2): 4, (7, 3): 2, (1, 3): 1, (6, 7): 1, (4, 8): 3, (8, 5): 4, (7, 6): 1, (3, 1): 1, (2, 1): 4, (6, 3): 3, (3, 6): 3, (3, 7): 2, (4, 2): 3, (2, 5): 7, (5, 2): 7, (2, 4): 3, (5, 8): 4, (8, 4): 3}

Debugged and modified from original source: https://gist.github.com/econchick/4666413

For more projects and code scripts, please visit my Github: https://github.com/MaximusWudy

#!/usr/bin/python
from collections import defaultdict
class Graph:
    def __init__(self):
        self.nodes = set() # set object
        self.edges = defaultdict(list)
        self.distances = {}
 
    def add_nodes(self, value):
        for i in value:
            self.nodes.add(i) # add element into set
 
    def add_edge(self, from_node, to_node, distance):
        self.edges[from_node].append(to_node)
        self.edges[to_node].append(from_node) # dict to neighbour nodes
        self.distances[(from_node, to_node)] = distance # dict for distance
        self.distances[(to_node, from_node)] = distance
 
 
# -------------------------------------
def dijkstra(graph, initial):
    visited = {initial: 0}
    path = {}
 
    nodes = set(graph.nodes)
 
    while nodes: 
        min_node = None
        for node in nodes:
            if node in visited:
                if min_node is None:
                    min_node = node
                elif visited[node] < visited[min_node]:
                    min_node = node
 
        if min_node is None:
              break
 
        nodes.remove(min_node)
        current_weight = visited[min_node]
 
        for edge in graph.edges[min_node]:
            weight = current_weight + graph.distances[(min_node, edge)]
            if edge not in visited or weight < visited[edge]:
                visited[edge] = weight
                path[edge] = min_node
 
    return visited, path
 
if __name__ == "__main__":
    g = Graph()
    g.add_nodes([i+1 for i in range(8)])
    g.add_edge(1, 2, 4)
    g.add_edge(1, 3, 1)
    g.add_edge(2, 4, 3)
    g.add_edge(2, 5, 7)
    g.add_edge(4, 8, 3)
    g.add_edge(5, 8, 4)
    g.add_edge(3, 6, 3)
    g.add_edge(3, 7, 2)
    g.add_edge(6, 7, 1)
    print "nodes:", g.nodes
    print "edges:", g.edges
    print "distances: ", g.distances
    # ----------
    print "-" * 25
    source_node = 1
    print "Source node:", source_node
    print dijkstra(g, 1) # return with visited and path

Dijkstra in Python