Listing the shortest path available using heapq for dijkstra shortest path algorithm

Question

I was given a task where I need to apply Dijkstra's Shortest Path Algorithm in my python code. Let say we have a few cities involved. I need to find the one that has the shortest route. In summary, the task is to:

Find the shortest route.
List all the possible paths.

I was successfully be able to find the shortest path among the cities, but I do not know how to list all the possible paths using heapq. Can anyone help me?

This is the graph I provided for better understanding of the graph:

The Code:

import heapq
from collections import defaultdict
global shortestPath
global shortestCost
shortestPath = "null"
shortestCost = 100000
def dijkstra(graph,src,dest): 
    h = []
  
    heapq.heappush(h,(0,src))
    global shortestPath
    global shortestCost
    global source
    while len(h)!=0:
        currcost,currvtx = heapq.heappop(h)
        if currvtx == dest:
            print("\t\t\t{} to {} with cost {}".format(src,dest,currcost))
            if currcost < shortestCost:
                if dest == src:
                    continue
                else:
                    shortestCost = currcost
                    shortestPath = dest
            break
        for neigh,neighcost in graph[currvtx]:
            heapq.heappush(h,(currcost+neighcost,neigh))

city = ["A","B","C","D","E","F"]
graph = defaultdict(list) 
graph["A"] = [("B",1),("C",5)]
graph["B"] = [('C', 6), ('D', 23)]
graph["C"] = [('E', 35)]
graph["D"] = [('F', 26)]
graph["E"] = [('D', 54)]

print ("\t=============================================================================")
print ("\t                     Dijkstra's Shortest Path Algorithm")
print ("\t=============================================================================")
print ("\n\tAssume 1 cost = 10 km")
print ("\n\tCity availability: {} ".format(city))
src = "A"
print ("\n\tPossible paths from {} :\n".format(src))
for i in city:
    dijkstra(graph,src,i)
print ("\n\t=============================================================================")
print("\t\tThe shortest path from {} is {} to {} with cost {}".format(src,src,shortestPath,shortestCost))
print ("\t=============================================================================")

The output:

    =============================================================================
                         Dijkstra's Shortest Path Algorithm
    =============================================================================

    Assume 1 cost = 10 km

    City availability: ['A', 'B', 'C', 'D', 'E', 'F'] 

    Possible paths from A :

            A to A with cost 0
            A to B with cost 1
            A to C with cost 5
            A to D with cost 24
            A to E with cost 40
            A to F with cost 50

    =============================================================================
        The shortest path from A is A to B with cost 1
    =============================================================================

My apologies if this post seems unfitting as this is my first question that I have posted in here.

Your help is highly appreciated. Thank you.

With that input, it just tells me "Invalid choice. Please enter another city:" For the purposes of demonstrating the issue, why not hardcode the dataset which reproduces the issue, and not take input? — Kenny Ostrom, Mar 12 '21 at 03:58
You can try type any input with Capital letters(from A to F). And yeah, I have the same idea like you too before, but I don't know how to do it. Sorry. — Muhammad Zahirul Iman, Mar 12 '21 at 04:02
Where there's an input(), get rid of it. Just assign the value you want to that variable, so it demonstrates the error. — Kenny Ostrom, Mar 12 '21 at 04:04
Looks good. I don't see any problems. To get the paths, just store a list of the path so far, along with its cost. — Kenny Ostrom, Mar 12 '21 at 06:31
I think you misunderstood the assignment, on finding the shortest overall path. That seems way too trivial. It probably just means print the path taken when you print each result from calling dijkstra's algorithm. To find "all possible paths" between the same two cities, you'd do a simple DFS or BFS, — Kenny Ostrom, Mar 12 '21 at 06:34
to get the path from dijkstra's, just push a different tuple on the heap. I'd suggest (cost, destination, path_so_far) — Kenny Ostrom, Mar 12 '21 at 06:52
Yeah I just realized that I misunderstood the question. Anyways, thanks for helping :) — Muhammad Zahirul Iman, Mar 12 '21 at 07:26

Listing the shortest path available using heapq for dijkstra shortest path algorithm

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