Is there a way to append to an external blend file?

Question

I know that bpy.data.libraries.load() allows me to append data from an external file to my current blender instance, but is there a way to do the reverse? Take something (let's say the default cube) and append it to an external file using the Python?

My exact need is to take a node group from the current blend file, and append it to an external blend file.

Answer 1

In Blender 2.78, bpy.data.libraries.write() will be an option to use, which will allow any datablock from the blend file to be saved to an external blend file.