Upgrading from cadquery-ocp<7.8 to cadquery-ocp>=7.8

[jdegenstein]

Reproduced a user report that during from build123d import * an error occurred: ImportError: cannot import name 'IVtkOCC_Shape' from 'OCP.IVtkOCC' (...\Lib\site-packages\OCP\IVtkOCC\__init__.py)

Traced it down and determined that if an environment previously contained e.g. cadquery-ocp==7.7.2.1 then upgrading to e.g. cadquery-ocp==7.8.x will cause this problem. I suspect that some of the VTK libraries in the older version are not uninstalled completely and are creating some conflicts.

The workaround is create a new clean environment from scratch and directly install the newer version of build123d (and its dependency cadquery-ocp>7.8).

[jdegenstein]

Another workaround if the installation is broken:

pip uninstall vtk
pip install vtk==9.3.1