I have the following list of lists of triples:

all_arcs = [[('Start', 2, 1), (2, 7, 1), (7, 'Stop', 1)],
           [('Start', 3, 2), (3, 6, 2), (4, 5, 2), (5, 'Stop', 2), (6, 4, 2)],
           [('Start', 1, 3), (1, 8, 3), (8, 9, 3), (9, 'Stop', 3)]]

Every sub-list in all_arcs is a triplet (i,j,k), that denotes the tour i->j of vehicle k. So for example, the first sub-list tells us that vehicle 1 has the tour Start -> 2 -> 7 -> Stop etc.

For every sub-list (<=> for every vehicle) in all_arcs I want to print out the tours in the following format:

Vehicle 1:     Start -> 2 -> 7 -> Stop

Vehicle 2:     Start -> 3 -> 6 -> 4 -> 5 -> Stop

Vehicle 3:     Start -> 1 -> 8 -> 9 -> Stop

...

(Vehicle n:     Start  -> ...  -> ...  -> Stop) depending on how many sub-list exists.

So I need to write a function that takes all_arcs as parameter and prints out the routes in the format above.

My attempt

So I thought It would be a good idea to "chain sort" all the sub-lists first. By chain sort I mean to go from (1,2,0),(3,4,0),(2,3,0) to (1,2,0),(2,3,0),(3,4,0), since the j index in previous triple is always the i index in the next. For the sorting, I used these functions and they worked well:

# function that obtains the next arc-tuple given list of tuples
def get_next_tuple(tup ,list_of_tuples):
  for i in range(len(list_of_tuples)):
      if tup[1] == list_of_tuples[i][0]:
        next_tuple = list_of_tuples[i]
  return next_tuple

# function that sorts the arc tuples in correct order
def sort_list_of_tuples(list_of_tuples):
  sorted_list = [list_of_tuples[0]]
  for i in sorted_list:
    if len(sorted_list) < len(list_of_tuples):
      sorted_list.append(get_next_tuple(i, list_of_tuples))
  return sorted_list

Now the printing, this is where I have problems:

for i, arcs in enumerate(all_arcs):
    sorted_arcs = sort_list_of_tuples(arcs)
    print(f'\nFork-lift {i+1}:')
    for j in range(len(sorted_arcs)):
        print(f'{sorted_arcs[j][0]} -> {sorted_arcs[j][1]}')
    print('\n-----------------------------------')

This obviously works and it prints out the correct order:

Vehicle 1:
Start -> 2
2 -> 7
7 -> Stop

-----------------------------------

Vehicle 2:
Start -> 3
3 -> 6
6 -> 4
4 -> 5
5 -> Stop

-----------------------------------

Vehicle 3:
Start -> 1
1 -> 8
8 -> 9
9 -> Stop

-----------------------------------

However, I either want it to print like the format above or(and) simply store the routes in simple lists, like this:

Vehicle 1 = [Start, 2, 7, Stop]

Vehicle 2 = [Start, 3, 6, 4, 5, Stop]
    
Vehicle 3 = [Start, 1, 8, 9, Stop]

The code is completely reproducible. I appreciate any help.

>Solution :

I would use dict:

all_arcs = [[('Start', 2, 1), (2, 7, 1), (7, 'Stop', 1)],
            [('Start', 3, 2), (3, 6, 2), (4, 5, 2), (5, 'Stop', 2), (6, 4, 2)],
            [('Start', 1, 3), (1, 8, 3), (8, 9, 3), (9, 'Stop', 3)]]

for arc in all_arcs:
    vehicle = arc[0][2]

    dct = {a: b for a, b, _ in arc} # a mapping of a point to another point

    current = 'Start'
    path = [current]

    while current != 'Stop':
        path.append(current := dct[current])

    print(f"Vehicle {vehicle}:", ' -> '.join(map(str, path)))

# Vehicle 1: Start -> 2 -> 7 -> Stop
# Vehicle 2: Start -> 3 -> 6 -> 4 -> 5 -> Stop
# Vehicle 3: Start -> 1 -> 8 -> 9 -> Stop

For each sublist (arc in the code), I construct a dictionary dct that maps a point to another point. Then chaining the paths according to this mapping is easier afterwards.