this is DFS.py file where I am trying to track down the algorithm execution using bunch of print statements,

=================DFS.py=========================== from graphs import Graph, Vertex  class DFSGraph(Graph):     def __init__(self):         super().__init__()         self.time = 0      def dfs(self):         for aVertex in self:             aVertex.setColor('white')             aVertex.setPred(-1)             self.dfsvisit(aVertex)      def dfsvisit(self, startVertex):         print("vertex {}: color {}".format(startVertex, startVertex.getColor()))         print("setting color gray")         startVertex.setColor('gray')         print("vertex {}: color {}".format(startVertex, startVertex.getColor()))         self.time += 1         startVertex.setDiscovery(self.time)         print("setting discovery time {} for vertex, {}".format(startVertex.getDiscovery(),startVertex ))         for nextVertex in startVertex.getConnections():             print("connections for vertex {} are {}. ".format(startVertex, startVertex.getConnections()))             print("     LOOP: vertex {}: color {}".format(nextVertex, nextVertex.getColor()))             if nextVertex.getColor() == 'white':                 nextVertex.setPred(startVertex)                 print("RECURSION: making recursive call on vertex {}".format(nextVertex))                 self.dfsvisit(nextVertex)         print("setting color black")         startVertex.setColor('black')         print("vertex {}: color {}".format(startVertex, startVertex.getColor()))         self.time += 1         startVertex.setFinish(self.time)         print("setting finish time {} for vertex, {}".format(startVertex.getFinish(), startVertex ))  if __name__ == '__main__':      g = DFSGraph()     g.addVertex('a')     g.addVertex('b')     g.addVertex('c')     g.addVertex('d')     g.addVertex('e')     g.addVertex('f')      a = g.getVertex('a')     b = g.getVertex('b')     c = g.getVertex('c')     d = g.getVertex('d')     e = g.getVertex('e')     f = g.getVertex('f')      g.addEdge(a,b)     g.addEdge(a,d)     g.addEdge(b,c)     g.addEdge(b,d)     g.addEdge(d,e)     g.addEdge(e,b)     g.addEdge(e,f)     g.addEdge(f,c)     g.dfs() 

this is graphs.py file which is being used to create a Graph.

class Vertex:     def __init__(self, key):         self.id = key         self.connectedTo = {}         self.distance = 0         self.color = "white"         self.pred = None         self.disc = 0         self.fin = 0      def addNeighbor(self, nbr, weight=0):         self.connectedTo[nbr] = weight      def __str__(self):         return str(self.id)      def getConnections(self):         return self.connectedTo.keys()      def getId(self):         return self.id      def getWeight(self, nbr):         return self.connectedTo[nbr]      def setDistance(self, distance):         self.distance = distance      def setPred(self, pred):         self.pred = pred      def getDistance(self):         return self.distance      def setColor(self, color):         self.color = color      def getColor(self):         return self.color      def setDiscovery(self,dtime):         self.disc = dtime      def getDiscovery(self):         return self.disc      def setPred(self,p):         self.pred = p      def getPred(self):         return self.pred      def setFinish(self,ftime):         self.fin = ftime      def getFinish(self):         return self.fin  class Graph:     def __init__(self):         self.vertList = {}         self.numVertices = 0      def addVertex(self, key):         self.numVertices = self.numVertices + 1         self.vertList[key] = Vertex(key)         return Vertex(key)      def getVertex(self, key):         return self.vertList.get(key)      def __contains__(self, n):         return n in self.vertList      def addEdge(self, origin, destination, cost=0):         if origin not in self.vertList:             self.addVertex(origin)         if destination not in self.vertList:             self.addVertex(destination)         self.vertList.get(origin).addNeighbor(self.vertList.get(destination), cost)      def getVertices(self):         return self.vertList.keys()      def __iter__(self):         return iter(self.vertList.values()) 

============= Output is really wrong and I am not sure why all vertexes are marked gray and black in the beginning 🙁 =============

$   ipython DFS.py vertex a: color white setting color gray vertex a: color gray setting discovery time 1 for vertex, a setting color black vertex a: color black setting finish time 2 for vertex, a vertex b: color white setting color gray vertex b: color gray setting discovery time 3 for vertex, b setting color black vertex b: color black setting finish time 4 for vertex, b vertex c: color white setting color gray vertex c: color gray setting discovery time 5 for vertex, c setting color black vertex c: color black setting finish time 6 for vertex, c vertex d: color white setting color gray vertex d: color gray setting discovery time 7 for vertex, d setting color black vertex d: color black setting finish time 8 for vertex, d vertex e: color white setting color gray vertex e: color gray setting discovery time 9 for vertex, e setting color black vertex e: color black setting finish time 10 for vertex, e vertex f: color white setting color gray vertex f: color gray setting discovery time 11 for vertex, f setting color black vertex f: color black setting finish time 12 for vertex, f vertex a: color white setting color gray vertex a: color gray setting discovery time 13 for vertex, a connections for vertex a are dict_keys([<graphs.Vertex object at 0x10f116e10>, <graphs.Vertex object at 0x10f1164e0>]).      LOOP: vertex b: color white RECURSION: making recursive call on vertex b vertex b: color white setting color gray vertex b: color gray setting discovery time 14 for vertex, b connections for vertex b are dict_keys([<graphs.Vertex object at 0x10f116ef0>, <graphs.Vertex object at 0x10f1164e0>]).      LOOP: vertex c: color white RECURSION: making recursive call on vertex c vertex c: color white setting color gray vertex c: color gray setting discovery time 15 for vertex, c setting color black vertex c: color black setting finish time 16 for vertex, c connections for vertex b are dict_keys([<graphs.Vertex object at 0x10f116ef0>, <graphs.Vertex object at 0x10f1164e0>]).      LOOP: vertex d: color white RECURSION: making recursive call on vertex d vertex d: color white setting color gray vertex d: color gray setting discovery time 17 for vertex, d connections for vertex d are dict_keys([<graphs.Vertex object at 0x10f116f28>]).      LOOP: vertex e: color white RECURSION: making recursive call on vertex e vertex e: color white setting color gray vertex e: color gray setting discovery time 18 for vertex, e connections for vertex e are dict_keys([<graphs.Vertex object at 0x10f116e10>, <graphs.Vertex object at 0x10f116eb8>]).      LOOP: vertex b: color gray connections for vertex e are dict_keys([<graphs.Vertex object at 0x10f116e10>, <graphs.Vertex object at 0x10f116eb8>]).      LOOP: vertex f: color white RECURSION: making recursive call on vertex f vertex f: color white setting color gray vertex f: color gray setting discovery time 19 for vertex, f connections for vertex f are dict_keys([<graphs.Vertex object at 0x10f116ef0>]).      LOOP: vertex c: color black setting color black vertex f: color black setting finish time 20 for vertex, f setting color black vertex e: color black setting finish time 21 for vertex, e setting color black vertex d: color black setting finish time 22 for vertex, d setting color black vertex b: color black setting finish time 23 for vertex, b connections for vertex a are dict_keys([<graphs.Vertex object at 0x10f116e10>, <graphs.Vertex object at 0x10f1164e0>]).      LOOP: vertex d: color black setting color black vertex a: color black setting finish time 24 for vertex, a vertex b: color white setting color gray vertex b: color gray setting discovery time 25 for vertex, b connections for vertex b are dict_keys([<graphs.Vertex object at 0x10f116ef0>, <graphs.Vertex object at 0x10f1164e0>]).      LOOP: vertex c: color black connections for vertex b are dict_keys([<graphs.Vertex object at 0x10f116ef0>, <graphs.Vertex object at 0x10f1164e0>]).      LOOP: vertex d: color black setting color black vertex b: color black setting finish time 26 for vertex, b vertex d: color white setting color gray vertex d: color gray setting discovery time 27 for vertex, d connections for vertex d are dict_keys([<graphs.Vertex object at 0x10f116f28>]).      LOOP: vertex e: color black setting color black vertex d: color black setting finish time 28 for vertex, d vertex c: color white setting color gray vertex c: color gray setting discovery time 29 for vertex, c setting color black vertex c: color black setting finish time 30 for vertex, c vertex e: color white setting color gray vertex e: color gray setting discovery time 31 for vertex, e connections for vertex e are dict_keys([<graphs.Vertex object at 0x10f116e10>, <graphs.Vertex object at 0x10f116eb8>]).      LOOP: vertex b: color black connections for vertex e are dict_keys([<graphs.Vertex object at 0x10f116e10>, <graphs.Vertex object at 0x10f116eb8>]).      LOOP: vertex f: color black setting color black vertex e: color black setting finish time 32 for vertex, e vertex f: color white setting color gray vertex f: color gray setting discovery time 33 for vertex, f connections for vertex f are dict_keys([<graphs.Vertex object at 0x10f116ef0>]).      LOOP: vertex c: color black setting color black vertex f: color black setting finish time 34 for vertex, f