It seems you called your function PointLight, I would strongly suggest against this because if it would not cause Python to get confused about whether to call your function or the Panda PointLight class you will at some point in the future be confused about it and mess up.
Other option that I suggest is you try with and without the shader autogeneration.
Look at the last section on this page closely : panda3d.org/manual/index.php/Lighting