KeyError: 'f'

[shripadc9]

from queue import Queue
#creating graph with 12 nodes and 17 edges
adj_list={"A":["B","D"],
"B":["A","C"],
"C":["B","I"],
"D":["A","E","f"],
"E":["D","F","G"],
"F":["A","E","H"],
"G":["E","H","L"],
"H":["F","G","L","K"],
"I":["C","J"],
"J":["I","K","F"],
"K":["J","H","L"],
"L":["G","H","K"] }

#create bfs

visited={} #create empty dictionary for keep track of visited node
level={} #create empty dictionary for keep track of level of each node
parent={} #create empty dictionary for keep track of parent of each node
bfs_travesal_output=[] #create empty lis for store of travesar order
queue=Queue() #empty queue

for node in adj_list.keys():
visited[node]=False
parent[node]=None
level[node]=-1

s="A"
visited[s]=True
level[s]=0
queue.put(s)

while not queue.empty():
u= queue.get()
bfs_travesal_output.append(u)

for v in adj_list[u]:
    if not visited[v]:
        visited[v]= True
        parent[v]= u
        level[v]= level[u]+1
        queue.put(v)

print(bfs_travesal_output)

KeyError Traceback (most recent call last)
in
39
40 for v in adj_list[u]:
---> 41 if not visited[v]:
42 visited[v]= True
43 parent[v]= u

KeyError: 'f'