# Learn Algorithm Design by Building a Shortest Path Algorithm - Step 34

### Tell us what’s happening:

Hey coders.

The instructions: `You should have a while loop that executes while unvisited is not empty. Don't forget the pass keyword.` I believe that’s what I did?

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

/* User Editable Region */

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 != ' ':
pass

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

#shortest_path(my_graph, 'A')

/* User Editable Region */

``````

User Agent is: `Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/120.0.0.0 Safari/537.36`

### Challenge Information:

Learn Algorithm Design by Building a Shortest Path Algorithm - Step 34

Ah, this one is a bit tricky. The step wants you to use “truthiness”. Basically, a list acts like True when it has element and like False when its empty.

2 Likes

Oh okay! But what am I supposed to put in the quotes/brackets? I tried `while unvisited = list(graph)` (what it was originally equal to, but that still shows an error.

The variable `unvisited` itself is a condition - its inherently going to act like True or False depending upon if its empty.

1 Like

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