Material settings for Blender Internal and Cycles? I've been working with Blender Internal for the past. Recently, to use HDR lighting, I switched to Cycles. Basically, I have a Python script that sets up my entire scene for Blender Internal. Now switching to Cycles, I notice I need to add a lot of new material specifications, because a lot of the old material specifications for Blender Internal are no longer  options in Cycles.

I am a bit confused here, because previously I've been thinking the two rendering engines will not differ in material settings. After all, my material is there, so why would changing the rendering engine has any impact on what is already there...

Is there a good strategy in terms of material settings for switching engines? Do I delete all the material settings and write new ones? I worry some of my old settings may still be in effect.
Cycles and Blender internal are entirely different render engines and that actually does mean yes the settings don't cross over - particularly for cycles, as it is a node-based material system. Nodes for one system don't cross over to the other. For example, blender internal materials you can turn reflectivity on or off, but in cycles you don't have a setting for that - rather, you add in a glossy shader and connect it to the world output shader, either directly through the world output node for a purely reflective shader, or through a mix/add node with other shaders. If you are unfamiliar with cycles materials, I'd recommend learning how they work with some intro tutorials. 

That being said, there are some attempts out there to convert blender internal materials into cycles materials, but I would pretty much always expect you will need to manually checkup on the material changes. This could get you most of the way for now though.

Edit: you do not have to worry about blender internal settings affecting cycles settings, as nothing is re-used between them.