当我运行我的程序时，为什么没有发生任何事情

Question

I tried to run the Dijkstra algorithm in Python. however, when I execute this code under Eclipse, there is nothing shown. I see that pydev understood all my imports and there is no error message.Can anyone point me in the right direction?

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

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

    def add_edge(self, from_node, to_node, distance):
        self._add_edge(from_node, to_node, distance)
        self._add_edge(to_node, from_node, distance) 

    def _add_edge(self, from_node, to_node, distance):
        self.edges.setdefault(from_node, [])
        self.edges[from_node].append(to_node)
        self.distances[(from_node, to_node)] = distance 
def dijkstra(graph, initial_node):
    visited = {initial_node: 0}
    current_node = initial_node
    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)
        cur_wt = visited[min_node]

        for edge in graph.edges[min_node]:
            wt = cur_wt + graph.distances[(min_node, edge)]
            if edge not in visited or wt < visited[edge]:
                visited[edge] = wt
                path[edge] = min_node 

    return visited, path

def shortest_path(graph, initial_node, goal_node):
    distances, paths = dijkstra(graph, initial_node)
    route = [goal_node]

    while goal_node != initial_node:
        route.append(paths[goal_node])
        goal_node = paths[goal_node]

    route.reverse()
    return route

if __name__ == '__main__':
    g = Graph()
    g.nodes = set(range(1, 7))
    g.add_edge(1, 2, 7)
    g.add_edge(1, 3, 9)
    g.add_edge(1, 6, 14)
    g.add_edge(2, 3, 10)
    g.add_edge(2, 4, 15)
    g.add_edge(3, 4, 11)
    g.add_edge(3, 6, 2)
    g.add_edge(4, 5, 6)
    g.add_edge(5, 6, 9)
    assert shortest_path(g, 1, 5) == [1, 3, 6, 5]
    assert shortest_path(g, 5, 1) == [5, 6, 3, 1]
    assert shortest_path(g, 2, 5) == [2, 3, 6, 5]
    assert shortest_path(g, 1, 4) == [1, 3, 4]

Answer 1

You are not printing anything. If assert doesn't fail, it won't show anything.

Instead of assert use print to know if shortest_path returns those arrays. (You can actually know it does because assert doesn't raise any errors).

Answer 2

Assuming that g is a graph object, you may try printing Nodes, edges and distances by following:

print g.nodes
print g.edges
print g.distances

It will help you to understand the graph structure and try using print instead of assert. In your case, these three lines will print the following:

set([1, 2, 3, 4, 5, 6])
{1: [2, 3, 6], 2: [1, 3, 4], 3: [1, 2, 4, 6], 4: [2, 3, 5], 5: [4, 6], 6:[1, 3, 5]}
{(1, 2): 7, (3, 2): 10, (1, 3): 9, (3, 6): 2, (4, 5): 6, (6, 1): 14, (3, 1): 9, (5, 4): 6, (2, 1): 7, (6, 3): 2, (5, 6): 9, (1, 6): 14, (4, 3): 11, (4, 2): 15, (2, 3): 10, (3, 4): 11, (2, 4): 15, (6, 5): 9}

Hope it helps!