graph = {
            0:[(1,24),(3,20),(2,3)],
            1:[(0,24)],
            2:[(0,3),(3,12)],
            3:[(2,12),(0,20)]
    }

from collections import defaultdict
from heapq import *

def dj(graph,source):
    dist = defaultdict(int)
    heap = [(0,source)]
    new_dist={}
    dist[source] = 0
    for i in range(1,4):
        heappush(heap,(10000,i))
        dist[i]=10000
    visited = set()
    while len(heap):
        c_dist,c_vertex = heappop(heap)
        if c_vertex not in visited:
            visited.add(c_vertex)
            for nbr,cost in graph[c_vertex]:
                if c_dist+cost < dist[nbr]:
                    dist[nbr] = c_dist+cost
            new_dist[c_vertex] = dist[c_vertex]
            while len(heap):
                heappop(heap)
            dist.pop(c_vertex)
            heap = [(disti,vertex) for vertex, disti in dist.items()]
            heapify(heap)

    print new_dist



dj(graph,0)