freeCodeCamp/curriculum/challenges/german/07-scientific-computing-with-python/learn-algorithm-design-by-building-a-shortest-path-algorithm/655791e6cf5e03be3de73451.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
655791e6cf5e03be3de73451	Schritt 45	20	step-45

--description--

If you try to uncomment your function call, it won't work. You have a couple of bugs to fix. The first one happens because in the nested if you are trying to access that might not exist in your paths dictionary. So, you need to be sure that paths[node] is not empty before accessing paths[node][-1].

Add an additional condition to your nested if statement to ensure that paths[node] is non-empty before accessing paths[node][-1].

--hints--

You should add paths[node] as the first condition to your nested if statement. Use the and operator to combine your conditions.

({ test: () =>  {
    const shortest = __helpers.python.getDef(code, "shortest_path");
    const {function_body} = shortest;    
    assert(function_body.match(/if\s+paths\s*\[\s*node\s*\]\s+and\s+paths\s*\[\s*node\s*\]\s*\[\s*-\s*1\s*\]\s*==\s*node\s*:/));
  }
})

--seed--

--seed-contents--

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]
--fcc-editable-region--                
                if paths[node][-1] == node:
                    paths[node] = paths[current]
--fcc-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')