graph = {'s': {'v':1,'w':4 },
         'v': {'w':2,'t':6},
         'w': {'t':3},
         't': {'': None}
         }
def dj(graph, start):
    Q = []# queue to hold all the vertices
    dist = {} #dictionary to hold all the distance
    prev = {} #dictionary to hold all the previous node visited

    for key in graph.keys():
        dist[key] = 1000
        prev[key] = ""
        Q.append(key)


    dist[start] = 0

    #I had to have another distance data structure dst
    # to store all the distance covered
    # I am not fond of it
    dst = []

    while Q:
        u = min(dist, key = dist.get)#Here I get the minimum distance
        Q.remove(u)#remove the min one from Q
        for v in graph[u]:
            #I also want to improvise this condition block
            #It is because of 't': {'': None}
            if graph[u][v] is None:
                continue
            alt = dist[u] + graph[u][v]
            if alt < dist[v]:
                dist[v] = alt
                prev[v] = u
        d = (dist.pop(u))
        dst.append(d)

    return dst,prev

print(dj(graph,'s'))