set faces without copying

def faces(self, faces):
        """ set faces without copying """
        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()