#529: improve error handling for missing vtk module

src/lbaf/IO/lbsGridStreamer.py

@@ -14,8 +14,8 @@ class GridStreamer:
 
     def __init__(
         self,
-        points: vtk.vtkPoints,
-        lines: vtk.vtkCellArray,
+        points, # vtk.vtkPoints
+        lines,  # vtk.vtkCellArry
         field_arrays: Optional[dict] = None,
         point_arrays: Optional[list] = None,
         cell_arrays: Optional[list] = None,
@@ -29,6 +29,9 @@ def __init__(
         if cell_arrays is None:
             cell_arrays = []
 
+        if not using_vtk:
+            raise ModuleNotFoundError("Could not find vtk module, which is required for the GridStreamer.")
+
         # Assign logger to instance variable
         self.__logger = logger