title: why is nothing happening when i run my program
body: <p>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?</p>
  
  <pre><code>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] &lt; 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 &lt; 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]
  </code></pre>