如何从odict_iterator中获取OrderedDict值？

Question

I am using the tsplib95 to parse .tsp files. I want to get a list of nodes out of the Problem class from tsplib95. I checked the documentation, the get_nodes() method returns an iter() over OrderedDict of nodes.

How do I access the values of the OrderedDict using the iterator? I can only ever iterate over the key values using the iterator.

The OrderedDict looks like this:
OrderedDict([(1, (20833.3333, 17100.0)), ..., (29, (27462.5, 12992.2222))])

I tried getting the coordinates value in a for loop and using the next () method.

            tsp_instance = tsplib95.load_problem(file.value)
            iterator = tsp_instance.get_nodes()

            print(next(iterator))
            print(iterator.__next__())

            for i in iterator:
                print(i)

But all of these only access the keys in the OrderedDict I do not know how to get the values of the coordinates when I do not have the original OrderedDict.

Answer 1

You will need to get a different iterator. The default iterator does not know the values, only the keys. For example

>>> od = OrderedDict([('a', 1), ('b', 2)])
>>> iterator = iter(od.items())
>>> print(list(iterator))
[('a', 1), ('b', 2)]

In Python 2, you can also do iterator = od.iteritems()

Answer 2

get_nodes() is not the tool you should be using for this. get_nodes() is only intended to return an iterator over nodes; the fact that this iterator is sometimes an iterator over an OrderedDict is an implementation detail, and it will not always be an OrderedDict iterator.

If you want to access the node coordinates of a problem instance that has node coordinates, you should use get_graph() and inspect the NetworkX node attributes ; the coordinates for a node will be under the 'coord' node attribute.