the advantage (and disadvantage) of [ the use of import vtk ] is that it imports everything. It requires just one import statement for all of VTK, but it can be slow because VTK has grown to be very large over the years.
Therefore we should avoid import vtk and import the vtkmodule that is required.
According to VTK documentation
Therefore we should avoid
import vtk
and import thevtkmodule
that is required.