# Learn Algorithm Design by Building a Shortest Path Algorithm - Step 47

### Tell us what’s happening:

i cant reproduce the bug in step 47. I try to change the start parameter but cant create a wrong path(its said that the bug is subtle, it will make the distance correct but the path list wrong) I’ve already solved by assigning a copy of list using slice, just very curious about the bug. Can anyone explain to me?

``````my_graph = {
'A': [('B', 3), ('D', 1)],
'B': [('A', 3), ('C', 4)],
'C': [('B', 4), ('D', 7)],
'D': [('A', 1), ('C', 7)]
}

def shortest_path(graph, start):
unvisited = list(graph)
distances = {node: 0 if node == start else float('inf') for node in graph}
paths = {node: [] for node in graph}
paths[start].append(start)

while unvisited:
current = min(unvisited, key=distances.get)
for node, distance in graph[current]:
if distance + distances[current] < distances[node]:
distances[node] = distance + distances[current]

# User Editable Region

if paths[node] and paths[node][-1] == node:
paths[node] = paths[current] [::]

# User Editable Region

else:
paths[node].extend(paths[current])
paths[node].append(node)
unvisited.remove(current)

print(f'Unvisited: {unvisited}\nDistances: {distances}\nPaths: {paths}')

shortest_path(my_graph, 'A')

``````

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