I’m trying to re-implement the scikit-surgerytutorial01 so I exactly followed all steps indicated in the documentation “https://scikit-surgerytutorial01.readthedocs.io/en/latest/01_VTK_Overlay_App.html” and I created a virtual environment where I installed all requirements with indicated versions on requirements.txt and .yml file. After, I created a file named overlay.py with the following code :

import sys
from PySide2.QtWidgets import QApplication
from sksurgeryutils.common_overlay_apps import OverlayBaseWidget
class OverlayApp(OverlayBaseWidget):
         def update_view(self):
                   _, image = self.video_source.read()
                   self.vtk_overlay_window.set_video_image(image)
                   self.vtk_overlay_window.Render()
if __name__ == '__main__':
         app = QApplication([])
         video_source = 0
         viewer = OverlayApp(video_source)
         model_dir = '../models'
         viewer.add_vtk_models_from_dir(model_dir)
         viewer.show()
         viewer.start()
         sys.exit(app.exec_())

When I execute this code I get :

(python_3.7_venv) younes@younes-ThinkPad-X1-Carbon-3rd:~/python_3.7_venv$ python overlay.py
Warning: Ignoring XDG_SESSION_TYPE=wayland on Gnome. Use QT_QPA_PLATFORM=wayland to run on Wayland anyway.
QWidget: Must construct a QApplication before a QWidget
Aborted (core dumped)

I’d like to know why I get this error: QWidget: Must construct a QApplication before a QWidget and how to deal with this problem.