GetAllDimensionNames and GetDimensions are not iterable (python)

[ecotner]

What version of OR-Tools and what language are you using?
Version: 8.1.8487
Language: Python

Which solver are you using (e.g. CP-SAT, Routing Solver, GLOP, BOP, Gurobi)
Routing Solver

What operating system (Linux, Windows, ...) and version?
Ubuntu 20.04 (via Windows Subsystem for Linux v2)

What did you do?
I have created a small script that reproduces the error:

from ortools.constraint_solver import pywrapcp

manager = pywrapcp.RoutingIndexManager(10, 2, 0)
routing = pywrapcp.RoutingModel(manager)

def some_callback(index):
    return 1

some_callback_index = routing.RegisterUnaryTransitCallback(some_callback)

routing.AddDimension(
    some_callback_index,
    slack_max=0,
    capacity=2**32 - 1,
    fix_start_cumul_to_zero=True,
    name="some_dimension"
)

names = routing.GetAllDimensionNames()
print(names) # prints `<Swig Object of type 'std::vector< std::string > *' at 0x7f05e4142ae0>`
print(dir(names)) # prints a list of attributes, none of which seem relevant for iteration/indexing
len(names) # raises TypeError
names[0] # raises TypeError
next(names) # raises TypeError

The same errors occur when you swap GetAllDimensionNames for GetDimensions as well.

What did you expect to see
I would expect these methods to either return a python list containing the dimension names/dimension objects, or some other container with __iter__ and __getitem__ methods so that the container can be iterated over or indexed into to retrieve the elements. It looks like someone also ran into this issue in #1417, but it was closed with the recommendation that the user should keep track of the dimensions themselves. I think it would be very convenient to have the ability to inspect the routing model itself rather than having to handle it manually!

What did you see instead?
I observed the TypeErrors mentioned in the comments of the script.

Make sure you include information that can help us debug (full error message, model Proto).

Anything else we should know about your project / environment

[Mizux]

Side note for myself: We should take a look at these lines

or-tools/ortools/util/python/vector.i

Lines 86 to 88 in fa84bc0

	PY_LIST_INPUT_OUTPUT_TYPEMAP(int, PyInt_Check, PyInt_FromLong);
	PY_LIST_INPUT_OUTPUT_TYPEMAP(int64, SwigPyIntOrLong_Check, PyLong_FromLongLong);
	PY_LIST_INPUT_OUTPUT_TYPEMAP(double, PyFloat_Check, PyFloat_FromDouble);

and see if we can add a std::vector<string>

note: Should also check Java and .Net wrappers

[Mizux]

Test

  print(f'list: {routing.GetAllDimensionNames()}')
  print(f'type: {dir(routing.GetAllDimensionNames())}')

current:

swig/python detected a memory leak of type 'std::vector< std::string > *', no destructor found.
list: <Swig Object of type 'std::vector< std::string > *' at 0x7f23b61d7ba0>
swig/python detected a memory leak of type 'std::vector< std::string > *', no destructor found.
type: ['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__int__', '__le__', '__lt__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__str__', '__subclasshook__', 'acquire', 'append', 'disown', 'next', 'own']

[Mizux]

now:

list: ['Distance', 'Time']
type: ['__add__', '__class__', '__class_getitem__', '__contains__', '__delattr__', '__delitem__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getitem__', '__gt__', '__hash__', '__iadd__', '__imul__', '__init__', '__init_subclass__', '__iter__', '__le__', '__len__', '__lt__', '__mul__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__reversed__', '__rmul__', '__setattr__', '__setitem__', '__sizeof__', '__str__', '__subclasshook__', 'append', 'clear', 'copy', 'count', 'extend', 'index', 'insert', 'pop', 'remove', 'reverse', 'sort']

[ecotner]

thank you @Mizux! Is this change pushed to pypi, or do I need to clone/build the master branch to be able to use the fix?

[Mizux]

master only, we hope to release a v9.0 ASAP once last issues are fixed (or postponed)
see: https://github.com/google/or-tools/milestone/17