vtkBoxWidget not working with PyQt5 application

Question

I am trying to embed vtk rendering code in PyQt5 with with QVTKRenderWindowInteractor . When I tried to use vtkBoxWidget inside it, program crashed. Without vtkBoxWidget (enclosed within two lines in below code ), its working fine. Can you please help me find the issue? I am trying to manually crop the rendered object using a bounding box with the help of vtkBoxWidget.

CODE :

from PyQt5.QtWidgets import QApplication, QWidget, QMainWindow, QFrame, QVBoxLayout
import sys
import vtk
from PyQt5 import QtGui
from vtk.qt.QVTKRenderWindowInteractor import QVTKRenderWindowInteractor

class MainWindow(QMainWindow):

    def __init__(self, parent=None):
        QMainWindow.__init__(self, parent)
        self.frame = QFrame()
        self.vl = QVBoxLayout()
        self.vtkWidget = QVTKRenderWindowInteractor(self.frame)
        self.vl.addWidget(self.vtkWidget)

        self.ren = vtk.vtkRenderer()
        self.vtkWidget.GetRenderWindow().AddRenderer(self.ren)
        self.iren = self.vtkWidget.GetRenderWindow().GetInteractor()
        self.iren.SetInteractorStyle(vtk.vtkInteractorStyleTrackballCamera())

        # Create source
        source = vtk.vtkSphereSource()
        source.SetCenter(0, 0, 0)
        source.SetRadius(5.0)

        # Create a mapper
        mapper = vtk.vtkPolyDataMapper()
        mapper.SetInputConnection(source.GetOutputPort())

        # Create an actor
        actor = vtk.vtkActor()
        actor.SetMapper(mapper)

        ###################################################################################
        boxWidget = vtk.vtkBoxWidget()
        boxWidget.SetInteractor(self.iren)
        boxWidget.SetPlaceFactor(1.0)
        boxWidget.SetRotationEnabled(0)
        planes = vtk.vtkPlanes()

        def ClipVolumeRender(obj, event):
            obj.GetPlanes(planes)
            mapper.SetClippingPlanes(planes)

        boxWidget.SetProp3D(actor)
        boxWidget.PlaceWidget()
        boxWidget.InsideOutOn()
        boxWidget.AddObserver("InteractionEvent", ClipVolumeRender)
        boxWidget.On()
        ###################################################################################

        self.ren.AddActor(actor)
        self.ren.ResetCamera()
        self.frame.setLayout(self.vl)
        self.setCentralWidget(self.frame)
        self.show()
        self.iren.Initialize()


if __name__ == "__main__":

    app = QApplication(sys.argv)
    window = MainWindow()
    sys.exit(app.exec_())

Answer 1

The problem is that boxWidget is a local variable that is eliminated by python, so afterwards the application tries to access that object but it no longer has allocated memory generating Segmentation fault . The solution is to extend the scope by changing boxWidget with self.boxWidget .