Dijkstra algorithm

from collections import defaultdict, deque

"""

~/v/H/p/s/py ❯❯❯ python3 dijkstra.py
{'G', 'B', 'E', 'A', 'D', 'F', 'C'}
{'A': 0}
nodes={'G', 'B', 'E', 'D', 'F', 'C'} visited={'B': 10, 'C': 20, 'A': 0} min_node=A
nodes={'G', 'E', 'D', 'F', 'C'} visited={'D': 25, 'E': 60, 'B': 10, 'C': 20, 'A': 0} min_node=B
nodes={'G', 'E', 'D', 'F'} visited={'D': 25, 'E': 60, 'B': 10, 'C': 20, 'A': 0} min_node=C
nodes={'G', 'E', 'F'} visited={'D': 25, 'E': 55, 'B': 10, 'C': 20, 'A': 0} min_node=D
nodes={'G', 'F'} visited={'B': 10, 'E': 55, 'A': 0, 'D': 25, 'F': 60, 'C': 20} min_node=E
nodes={'G'} visited={'B': 10, 'E': 55, 'A': 0, 'D': 25, 'G': 62, 'F': 60, 'C': 20} min_node=F
nodes=set() visited={'B': 10, 'E': 55, 'A': 0, 'D': 25, 'G': 62, 'F': 60, 'C': 20} min_node=G
(25, ['A', 'B', 'D'])

"""



class Graph(object):
    def __init__(self):
        self.nodes = set()
        self.edges = defaultdict(list)
        self.distances = {}

    def add_node(self, value):
        self.nodes.add(value)

    def add_edge(self, from_node, to_node, distance):
        self.edges[from_node].append(to_node)
        self.edges[to_node].append(from_node)
        self.distances[(from_node, to_node)] = distance


def dijkstra(graph, initial):
    visited = {initial: 0}
    path = {}

    nodes = set(graph.nodes)
    print(nodes)
    print(visited)

    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]
        # enumerate all adjacent nodes of min_node
        for node in graph.edges[min_node]:
            try:
                weight = current_weight + graph.distances[(min_node, node)]
            except:
                continue
            if node not in visited or weight < visited[node]:
                visited[node] = weight
                path[node] = min_node
        print("nodes=%s visited=%s min_node=%s" % (nodes, visited, min_node))

    return visited, path


def shortest_path(graph, origin, destination):
    visited, paths = dijkstra(graph, origin)
    full_path = deque()
    _destination = paths[destination]

    while _destination != origin:
        full_path.appendleft(_destination)
        _destination = paths[_destination]

    full_path.appendleft(origin)
    full_path.append(destination)

    return visited[destination], list(full_path)

if __name__ == '__main__':
    graph = Graph()

    for node in ['A', 'B', 'C', 'D', 'E', 'F', 'G']:
        graph.add_node(node)

    graph.add_edge('A', 'B', 10)
    graph.add_edge('A', 'C', 20)
    graph.add_edge('B', 'D', 15)
    graph.add_edge('C', 'D', 30)
    graph.add_edge('B', 'E', 50)
    graph.add_edge('D', 'E', 30)
    graph.add_edge('E', 'F', 5)
    graph.add_edge('F', 'G', 2)

print(shortest_path(graph, 'A', 'D')) # output: (25, ['A', 'B', 'D'])