This repo demonstrates the Python scripting in Blender Cycles Render for blender v2.78. It shows how to create multiple materials and shade them differently, and render them using a Python script that can be run from the command line in the background. This is a ready to run code. It has 5 .stl mesh files corresponding to a convecting water bubble. The script loops through these files and creates and saves the render images. To run this code, do the following in the command line in this directory.

<path_to_blender_exec> --background --python BlenderCyclesTest.py

<path_to_blender_exec> will look like for eg. ./blender.app/Contents/MacOS/blender

This will create 5 images in this directory.

The basic idea is to create a scene using the blender GUI - load a single .stl file in the blender GUI, and set the background, camera angle and lighting for the scene. Make sure that the render looks the way you want. Then delete the object (here it is the water drop), and save the scene as a .blend file (Here it is DropScene.blend). The Python script will load the .blend file, and the object (the moving water drop) will be loaded inside the for loop in the python script.