Whats wrong with this code?

[student1]

def dijkstra1(successors, other_node):
    vertices : length = successors
    n = len(successors)
    S = []
    S.append(0)
    L = dict()
    L[0] = 0
    P = dict()
    P[0] = '-'
    for vertex in vertices:
        L[vertex] = float("inf")
        P[vertex] = None

    dist[source] = 0
    Q = set(vertices)

    while len(Q) > 0:
        u = minimum_distance(dist, Q)
        print('Currently considering', u, 'with a distance of', dist[u])
        Q.remove(u)

        if L[u] == float('inf'):
            break

        n = get_neighbours(graph, u)
        for vertex in n:
            alt = dist[u] + dist_between(graph, u, vertex)
            if alt < L[vertex]:
                L[vertex] = alt
                P[vertex] = u
    return L[other_node]

says that the L[vertex]=float["inf"] is a unhashable type 'dict'. What does that mean and how do I fix it?

[skorpius_]

What's going on in line 2?

what do you get for these outputs:

print type(vertices)
print type(vertex)

?