# SelectedVerticesAndEdges

VTKExamples/Python/Graphs/SelectedVerticesAndEdges

### Description

*Contributed by Eric Monson

### Code

SelectedVerticesAndEdges.py

    #!/usr/bin/env python
    from __future__ import print_function

    import vtk

    source = vtk.vtkRandomGraphSource()
    source.Update()

    view = vtk.vtkGraphLayoutView()
    view.AddRepresentationFromInputConnection(source.GetOutputPort())

    def selectionCallback(caller, event):

        # In C++ there is some extra data passed to the callback, but in Python
        # the callback data is lost...

        # There should be two selection nodes, but which one is vertices and which
        # is edges does not seem to be guaranteed...
        sel = caller.GetCurrentSelection()
        node0 = sel.GetNode(0)
        node0_field_type = node0.GetFieldType()
        sel_list0 = caller.GetCurrentSelection().GetNode(0).GetSelectionList()
        node1 = sel.GetNode(1)
        node1_field_type = node1.GetFieldType()
        sel_list1 = caller.GetCurrentSelection().GetNode(1).GetSelectionList()

        if (sel_list0.GetNumberOfTuples() > 0):
            printFieldType(node0_field_type)
            for ii in range(sel_list0.GetNumberOfTuples()):
                print("\t", sel_list0.GetValue(ii))

        if (sel_list1.GetNumberOfTuples() > 0):
            printFieldType(node1_field_type)
            for ii in range(sel_list1.GetNumberOfTuples()):
                print("\t", sel_list1.GetValue(ii))

            print("- - -")

    def printFieldType(field_type):

        if field_type == 3:
               print("Vertices Selected:")
        elif field_type == 4:
               print("Edges Selected:")
        else:
               print("Unknown type:")

    rep = view.GetRepresentation(0)

    # The vtkRenderedGraphRepresentation should already have a vtkAnnotationLink,
    # so we just want to grab it and add an observer with our callback function
    # attached
    link = rep.GetAnnotationLink()
    link.AddObserver("AnnotationChangedEvent", selectionCallback)

    view.GetRenderWindow().SetSize(600, 600)
    view.ResetCamera()
    view.Render()
    view.GetInteractor().Start()