I am trying to complete the project on https://www.codecademy.com/paths/computer-science/tracks/complex-data-structures/modules/cspath-graphs/projects/maze-explorer

Here is my code for graph.py

```
from vertex import Vertex
class Graph:
def __init__(self):
self.graph_dict = {}
def add_vertex(self, node):
self.graph_dict[node.value] = node
def add_edge(self, from_node, to_node, weight = 0):
self.graph_dict[from_node.value].add_edge(to_node.value, weight)
self.graph_dict[to_node.value].add_edge(from_node.value, weight)
def explore(self):
print("Exploring the graph....\n")
#FILL IN EXPLORE METHOD BELOW
current_room = "entrance"
path_total = 0
print("\nStarting off at the {0}\n".format(current_room))
while current_room != "treasure room":
node = self.graph_dict[current_room]
for connected_room, weight in node.edges.items():
key = connected_room[0]
print("enter {0} for {1}: {2} cost".format(key, connected_room, weight))
valid_choices = [character[0] for character in node.edges.key()]
print("\nYou have accumulated: {0} cost".format(path_total))
choices = input("\nWhich room do you move to?")
def print_map(self):
print("\nMAZE LAYOUT\n")
for node_key in self.graph_dict:
print("{0} connected to...".format(node_key))
node = self.graph_dict[node_key]
for adjacent_node, weight in node.edges.items():
print("=> {0}: cost is {1}".format(adjacent_node, weight))
print("")
print("")
def build_graph():
graph = Graph()
# MAKE ROOMS INTO VERTICES BELOW...
entrance = Vertex("entrance")
ante_chamber = Vertex("ante_chamber")
kings_room = Vertex("king's room")
grand_gallery = Vertex("grand gallery")
treasure_room = Vertex("treasure room")
# ADD ROOMS TO GRAPH BELOW...
graph.add_vertex(entrance)
graph.add_vertex(ante_chamber)
graph.add_vertex(kings_room)
graph.add_vertex(grand_gallery)
graph.add_vertex(treasure_room)
# ADD EDGES BETWEEN ROOMS BELOW...
entrance.add_edge(ante_chamber, 7)
entrance.add_edge(kings_room, 3)
kings_room.add_edge(ante_chamber, 1)
grand_gallery.add_edge(ante_chamber, 2)
grand_gallery.add_edge(kings_room, 2)
treasure_room.add_edge(ante_chamber, 6)
treasure_room.add_edge(grand_gallery, 4)
# DON'T CHANGE THIS CODE
graph.print_map()
return graph
```

what is wrong here?