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 :