freeCodeCamp/curriculum/challenges/german/07-scientific-computing-with-python/learn-algorithm-design-by-building-a-shortest-path-algorithm/6557913b8fe5c0bc834c9f4f.md

id, title, challengeType, dashedName

id	title	challengeType	dashedName
6557913b8fe5c0bc834c9f4f	Step 47	20	step-47

--description--

The .extend() method, allows you to add elements from an iterable to the end of a list:

my_list = ['larch', 'birch']
tree_list = ['fir', 'redwood', 'pine']
my_list.extend(tree_list)
print(my_list) # Output: ['larch', 'birch', 'fir', 'redwood', 'pine']

Create an else clause and use the .extend() method to add the current node path to the neighbor node path.

--hints--

You should create an else clause after your nested if statement.

({ test: () =>  {
    const commentless_code = __helpers.python.removeComments(code);
    const {block_body} = __helpers.python.getBlock(commentless_code, /if\s+distance\s*\+\s*distances\s*\[\s*current\s*\]\s*<\s*distances\s*\[\s*node\s*\]\s*/);
    assert(block_body.match(/^\s+else\s*:/m));
  }
})

You should have paths[node].extend(paths[current]) in your else clause.

({ test: () =>  {
    const shortest = __helpers.python.getDef(code, "shortest_path");
    const {function_body} = shortest;
    assert(function_body.match(/^(\s*)if\s+paths\s*\[\s*node\s*\]\s*\[\s*-\s*1\s*\]\s*==\s*node\s*:\s*^\1(\s{4})paths\s*\[\s*node\s*\]\s*=\s*paths\s*\[\s*current\s*\]\s*^\1else\s*:\s*^\1\2paths\s*\[\s*node\s*\]\s*\.extend\s*\(\s*paths\s*\[\s*current\s*\]\s*\)/ms));
  }
})

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

#shortest_path(my_graph, 'A')