code: def faces(self, faces):
          
          if faces.dtype != vtki.ID_TYPE:
              faces = faces.astype(vtki.ID_TYPE)
  
          # get number of faces
          if faces.ndim == 1:
              log.debug('efficiency warning')
              c = 0
              nfaces = 0
              while c < faces.size:
                  c += faces[c] + 1
                  nfaces += 1
          else:
              nfaces = faces.shape[0]
  
          vtkcells = vtk.vtkCellArray()
          vtkcells.SetCells(nfaces, numpy_to_vtkIdTypeArray(faces, deep=False))
          if faces.ndim > 1 and faces.shape[1] == 2:
              self.SetVerts(vtkcells)
          else:
              self.SetPolys(vtkcells)
          self._face_ref = faces
          self.Modified()
docs: set faces without copying