Cleaned up the code and added comments to help understand the code. Fixed the return value to to be a list of tuples.

degrees.py

@@ -93,41 +93,45 @@ def shortest_path(source, target):
 	"""
 	frontier = QueueFrontier()
 	explored = StackFrontier()
+	# Create our initial node, since this is the starting node there will be no parent node.
+	# No need to worry about populating a movie_id.
 	frontier.add(Node(source, None, None))
-	results = [[]]
+	results = []
 	
-	while frontier:
+	while not frontier.empty():
 		currentNode = frontier.remove()
-		
+		# Is the currentNode's state (person_id) equal to the target (also a person_id)?
 		if currentNode.state == target:
 			tmp = currentNode
-			print("Found %s" %(people[tmp.state]))
+			# If so, loop over the currentNode's parents, grandparents and so forth until we hit a node
-			print("Found!")
+			# that has no parent node.
-			cost = 0
-			r = []
-			r.append(tmp)
-			index = len(results)
-			
 			while tmp:
-				if not tmp.parent:
+				# If the parent node is None, then that means we've hit the last node in the list.
-					r.append(tmp.parent)
+				# So, we won't be adding this tmp node to the result listing as it is the source.
-					print("Parent found! %s" %(people[tmp.state]))
+				if not tmp.parent == None:
+					results.append((tmp.action, tmp.state))
 					
 				tmp = tmp.parent
-				cost+=1
+			# Since we traversed the target node's parents from bottom up, so reverse the list to present the order of the connections
-			results.append(r)
+			# in the order the caller code is expecting.
-			print("Estimated Cost %d" %(cost))
+			results.reverse()
-			#break
+			print(results)
+			break
 		
-		if not explored.contains_state(currentNode.state):
+		# currentNode.state has person ID.
-			# currentNode.state has person ID.
+		neighbors = neighbors_for_person(currentNode.state)
-			neighbors = neighbors_for_person(currentNode.state)
+		# currentNode has been explored, so add it it the explored stack.
-			explored.add(currentNode)
+		explored.add(currentNode)
+		
+		for i in neighbors:
+			# i is a pair (movie_id, person_id), so i[i] contains the person_id.
+			if not explored.contains_state(i[1]):
+				# i[0] contains movie_id (this seemed like the best thing to use for the "action" parameter of the Node object for)
+				# currentNode is being set as the parent node of the new node being added to the frontier
+				# i[1] contains person_id 
+				frontier.add(Node(i[1], currentNode, i[0]))
 			
-			for i in neighbors:
+	return None
-				frontier.add(Node(i[1], currentNode, None))
-			
-	return results
 
 def person_id_for_name(name):
 	"""