The MapScalars() methods leak in Python

When called from Python, the MapScalars() methods leak the vtkUnsignedCharArray that they return. To avoid the leak, they need the VTK_NEWINSTANCE hint.

These methods appear in vtkScalarsToColors and vtkMapper. In addition to adding the hint, the wrappers can be made to warn if they encounter an unhinted MapScalars() method that returns a VTK array.

In fact, any VTK method that returns a VTK object but isn't a getter (i.e. doesn't start with Get) has a fair probability of needing a hint.

Ref: https://discourse.vtk.org/t/retrieve-the-mapped-colors-from-vtkopenglpolydatamapper/12760